"Dirty" brief warmup through Tuesday with clouds and some showers; cooler for rest of week with potential heavy rains southeast of St. Lawrence Valley Wednesday to Friday; drier but still cool next weekend before potential but uncertain gradual warmup following week into mid-May

Plain-language summary:

 

After a cool and dry day today except light rain in eastern Maine, some showers will affect northern areas late tonight before a brief warmup on Monday and Tuesday ensues, but with relatively cloudy skies for most and scattered showers along and northwest of the Appalachians on Tuesday. It will be rather windy on Tuesday, especially in the St. Lawrence and Champlain Valleys. It will then turn cooler for the rest of the week for everyone and potentially very wet southeast of the St. Lawrence Valley for Wednesday through Friday. It turns drier but remains cool next weekend, though pop-up scattered showers are still possible depending on subtle disturbances that are uncertain at this time. It could gradually turn warmer, or at least with pushes of warmth becoming more possible, later in the following week into mid-May, though the extent of the change is uncertain.

 

Meteorological discussion:

 

Cool and dry except light rain in eastern Maine today, then brief warmup through Tuesday with scattered showers and windy conditions for Tuesday

 

The slow-moving storm that I mentioned in the blog post a week ago ended up moving faster and was weaker than modeled back then, with a somewhat less amplified and block weather pattern. It seems like models tend to have a bias for showing very anomalous and blocked patterns in the medium to long range. In any case, that storm is way off to the northeast, but there is still unseasonably cool air in almost the entire eastern North America associated with a classic upper-level ridge/trough pattern in western/eastern North America (+PNA), with the dip in the jet stream in eastern North America aided by high-latitude blocking (-NAO). Actually, another storm is rapidly intensifying off the U.S. East Coast and will bring heavy rain to Atlantic Canada through tonight, with eastern Maine getting overcast skies and light rain on the western edge of the storm. Otherwise, it is mostly dry today though still not particularly sunny given leftover mid-level moisture and the cold air aloft leading to some instability. However, the upper-level trough will reinforce itself over central North America through Tuesday, which is associated with a low-pressure system tracking across northern Ontario into northern Quebec Monday into Tuesday, which will temporarily lead to deeper southwesterly flow and a warmup in our region. It will be a "dirty" warmup with some warm-advection light rain in northern areas late tonight and clouds and scattered showers along and northwest of the Appalachians on Tuesday. On Tuesday, many lower-elevation areas southeast of the St. Lawrence Valley, where there is more sunshine, could surpass 70F (21C). The pressure gradient between the high-pressure system over the western Atlantic and the low-pressure system over James Bay will lead to strong southerly to southwesterly winds on Tuesday, especially in the St. Lawrence and Champlain Valleys, where wind channeling will enhance the winds.

 

Source: TropicalTidbits

 

Cool for rest of the week for everyone, potentially very wet southeast of St. Lawrence Valley Wednesday through Friday

 

However, the warmth will not last, as the broad upper-level trough gradually moves east into our region for the rest of the week and into next weekend. A cold front will slowly pass through the region Tuesday night, but another low-pressure system will track along the front on Wednesday, likely bringing a steady, soaking rain to areas southeast of the St. Lawrence Valley, though models have not agreed on the exact location yet. Yet another potentially stronger low-pressure system will likely follow not far behind as it tracks from Colorado to near the U.S. East Coast from Wednesday to Friday, strengthening as it feeds on the still strong northwest-southeast temperature gradient. However, the trajectory of this storm is even more uncertain, with model runs a few days ago suggesting it could go right into our region, bringing heavy rain and strong winds, whereas most models today show it far enough east for only areas southeast of the St. Lawrence Valley to receive rain, or even close to a total miss for our region. In either case, our region will be on the cool, northern side of the two systems, favoring a cold, steady rain instead of the scattered showers and thunderstorms that are more common in the warm season. If the two storms track over the same area, parts of our region could receive >2" (50 mm) of rain from Wednesday to Friday.

 

Source: TropicalTidbits

 

Source: Climate Prediction Center

 

Drier but still cool next weekend 

 

Once the upper-level trough is right over our region next weekend and any front is pushed south of becomes more diffuse, major storms are less likely, with it still being cooler than average but with less rain. With cold air aloft but no real strong push of low-level cold arctic air anymore, sunshine will still prevent highs from being more than 10F (6C) below average for most, with the daytime heating leading to some instability and cumulus clouds and possibly showers depending on any forcing from subtle disturbances that cannot be foreseen this far out. There could another storm ejecting from the Rockies next weekend and approaching our region early the following week, though the overall blocking pattern and west-northwesterly flow across the region could push the storm entirely to the south.

 

Source: TropicalTidbits

 

Potential but uncertain change to more warmth for mid-May 

 

There are some signs of the persistent cool, unsettled weather pattern slowly breaking down for the following week, though models disagree on the extent of the change. Current projections are for the AO to turn slightly more positive, with the NAO turning closer to neutral heading into mid-May, which would promote a breakdown of the blocking pattern and is less favorable for persistent deep upper-level troughs in eastern North America. There is already a lack of true arctic air, and that will likely continue to be the case, with any cold air mass being able to be quickly modified by the strong May sunshine unless it is continuously reinforced. The PNA will also turn closer to neutral. All of this means that pushes of warmth from the southwest actually become more possible for later in the following week into mid-May, though how much of the warmth reaches our region is questionable, and many models still insist on some upper-level troughing stuck to the northeast of our region that would block some or possibly most of the warmth, in which case the battle could actually lead to yet more clouds and rain, but there is considerable model disagreement on this. I would not be surprised if the models are not persistent enough with the current pattern, and if any change to a warmer pattern is delayed, but time will tell.

 

Source: TropicalTidbits

 

Dry and sunny stretch continues through Tuesday with warming trend; likely cool and rainy late week, tapering off to showers next weekend; relatively cool, cloudy, and unsettled following week by early May standards but specific details and timing of systems uncertain

Plain-language summary:

 

The relatively dry and sunny stretch will continue through Tuesday with a gradual warming trend. Then, some showers are likely for Wednesday before it likely turns cool and rainy for Thursday and Friday with scattered showers still likely next weekend, though there is still a possibility for drier weather if the storm stays to our east. If the setup is right, higher elevations could even see wet snow mixed in. Whatever storm that occurs will weaken and move away for the following week, but it will likely remain relatively cool, cloudy, and unsettled on most days by early May standards, though the slow-moving and blocked weather pattern makes any specific details and timing of any systems or brief warmer and/or drier breaks impossible to discern for now.

 

Meteorological discussion:

 

Dry, mostly sunny weather continues through Tuesday with gradual warming trend 

 

This past week has been mostly dry and rather sunny for most, in stark contrast to the previous week. The dry weather will continue through Tuesday as a baroclinic zone and weak low-pressure system to the southwest that produced rain has weakened, with broad weak surface high-pressure now dominating. It will also gradually turn warmer, with temperatures actually expected to be above average by Tuesday except along the coast with onshore southerly winds off the Gulf of Maine that is still cold from last winter. Tuesday will likely be the warmest day for a long time afterward (10 days or more) in most of the region. The continental-scale weather pattern is rather blocked (-NAO and -AO), causing systems to move rather slowly. In this case, the weather pattern consists of a persistent closed upper-level low over the Canadian Prairies, bringing snow for days there, and a persistent closed upper-level ridge over northern Quebec blocking storminess from approaching from the west, leading to dry weather in our region.

 

Source: TropicalTidbits

 

Source: Climate Prediction Center

 

Cooler, rainy weather likely to dominate late week into next weekend, with heaviest on Thursday and Friday before tapering off to showers next weekend 

 

However, the weather pattern will slowly move eastward. A storm ejecting from the central Rockies today will slowly move northeast, elongate, and shear out as it attempts to move into the Quebec upper-level ridge by Wednesday, but there will still be enough left of the storm to produced increased clouds and some showers, but not nearly as much rain as areas farther west. However, by this point, the whole weather pattern will have moved eastward. A second storm will form and strengthen behind the shearing out storm on Thursday near the U.S. East Coast, and most models show this storm getting stuck over Maine, New Brunswick, or eastern Quebec on Friday and Saturday as it occludes and then slowly weakens while remaining almost stationary through early the following week. This would lead to an extended period of cloudy, rainy, and cool weather, first steadier rain on Thursday and Friday before tapering off to scattered showers by next weekend. Given the low-pressure location at or to the east of our region, northwesterly winds will initially pull down cold air from the subarctic or arctic. Although the arctic air masses are rapidly weakening as spring progresses, this cold air, combined with ascent, precipitation, and cloud cover in the storm leading to dynamic cooling, some models are even showing higher-elevation wet snow. As is always the case with blocked patterns, there is still considerable uncertainty in this scenario. It is possible that everything moves faster (weather pattern is slightly less blocked, like the GFS model shows today), and the secondary storm develops a little too far east to affect most of our region except for Maine, with the rest of the region experiencing cool but drier weather for late week into the weekend, like models showed a few days ago. After occlusion next weekend, the storm will weaken and cut-off, therefore cutting off the supply of cold air, leading to the cold pool becoming stale with the early May sun angle moderating it, which should end any snow or even any steady precipitation.

 

Source: TropicalTidbits

 

Source: TropicalTidbits

 

Relatively cool, cloudy, and unsettled likely to dominate following week, but with specific details and timing of any systems being very uncertain 

 

Whatever storm that occurs will eventually move off to the east in a much weakened state later the following week, but no prolonged warm and/or dry periods are expected. Below-average temperatures will generally dominate as the -NAO and -AO pushes the jet stream southward, allowing Canadian air to dominate the weather pattern, and the +PNA (upper-level ridging in western North America) focuses the cooler air into eastern North America. This is a stunning reversal from March and earlier in April that was dominated by record warmth in the contiguous U.S., especially southwest of our region. However, it is possible that the pattern is blocked enough to prevent much access of arctic air, in which case even the air masses coming out of southern Canada will be only marginally cooler than average. Still, the pattern will almost certainly block any intense warmth from the southern and western U.S. True cold periods may be more tied to any cloudier and rainier periods than arctic outbreaks. Models are inconsistent with any specific details or timing of any features, and with a blocked pattern, it is best not to speculate. But upper-level troughing dominating our region favors cool, unsettled, and relatively cloudy weather (for early May standards), even if models disagree on the magnitude and persistence of such a pattern and if there are any brief breaks of warmer, drier weather.

 

Source: TropicalTidbits

Warmth ends with rain and snow today before mostly dry upcoming week; hard freeze Monday night before seasonably cool with stable temperatures later in week; seasonable temperatures likely to continue into following week, perhaps mostly dry early on before turning wetter and cooler

Plain-language summary:

 

After being unseasonably warm for most yesterday, especially west of the Appalachians, it is abruptly and dramatically colder today with a cold rain at lower elevations and even wet snow at higher elevations with minor accumulations. After a few scattered snow showers tonight, it will be a mostly dry upcoming week. It first turns colder and drier with a hard freeze expected Monday night before moderating with sunshine on Tuesday. After a few scattered rain or snow showers Wednesday into Wednesday night in Maine and Eastern Townships of Quebec, seasonably cool and dry weather with partly to mostly sunny skies is then expected through next weekend with relatively little day-to-day temperature variations. Temperatures will likely remain relatively seasonable for the following week, perhaps mostly dry to start before turning wetter and cooler later in the week, though that is a bit more uncertain.

 

Meteorological discussion: 

 

Warmth ends abruptly and dramatically with cold rain in lower elevations and wet snow for higher elevations today, then colder and drier with hard freeze Monday night before moderating Tuesday 

 

Yesterday was the last really warm day (especially west of the Appalachians) for our region for 10 days or likely longer. A sharp cold front passing through today with much colder air from the subarctic or arctic is leading to temperatures being 20-30F (11-17C) cooler than yesterday for most, with rain for many as a disturbance riding along the cold front leads to lingering precipitation behind the front for a few hours before drier air moves in. In higher elevations, the rain will change to snow, with minor accumulations possible though limited by marginal temperatures and daytime occurrence (which matters a lot now given the high late April sun angle). Wet snow fell briefly even in lower elevations of the St. Lawrence and Champlain Valleys this morning with isolated areas of minor accumulations. A weak secondary front will bring scattered snow showers tonight, mostly areas along and northwest of the Appalachians, before clearing by Monday. Again, given marginal temperatures, accumulations will be mostly at higher elevations, though the nighttime occurrence will remove the inhibition by the April sun angle. The front will bring an even colder shot of air directly from the north, with a hard freeze expected Monday night as winds lighten with the cold surface high-pressure system directly over our region and skies remain clear. The cold shot will be relatively brief, with the surface high-pressure system already sliding southeast of our region by later Tuesday, allowing the northerly flow to shift to a southerly flow and the April sun angle to quickly moderate the cold air mass.

 

Source: TropicalTidbits

 

Seasonably cool and mostly dry with relatively small day-to-day temperature fluctuations late week into weekend 

 

A rapidly dropping NAO and AO into negative territory signals high-latitude blocking building over the next week or two, the opposite of most of March and April thus far. It is impressive with a strong Greenland cut-off upper-level ridge overtop a strong cut-off upper-level low over Atlantic Canada. This pushes the storm track and jet stream south of our region, as well as slows down all the weather systems, while also allowing cool air from the higher latitudes to dominate and preventing any of the persistent summerlike air in the southern and central U.S. from reaching our region. I alluded to this in my blog post a week ago, but at that time, models indicated one more warmup later this upcoming week beforehand, which no longer is likely. The PNA turning positive is also aiding this shift. However, ironically, at the same time, the cold air at high latitudes is rapidly weakening compared to the earlier incredibly cold strong air masses (including the coldest April temperature on record in Quebec of -40.4C on April 1). This means that after the cold shot through Tuesday, even the cooler air masses from the northwest will not be far below average, especially on sunnier days given the strong late April sun angle. The push of storm track to our south will also lead to a drier weather pattern, and the lack of strong temperature contrasts will lead to relatively stable temperatures from one day to the next, with no particularly cold or hot days.

 

Source: Climate Prediction Center

 

There is a weak backdoor mostly dry cold front likely Wednesday that will temporarily bring increased clouds and maybe a few scattered showers (possibly mixing with snow with little or no accumulation) in Maine and the Eastern Townships of Quebec. Then, a surface high-pressure system parks over far northern Quebec through next weekend, whose cooler air will battle with warm, moist air over the central U.S. along a stationary diffuse front or baroclinic zone likely near or just southwest of our region, a symptom of the developing blocking pattern. Given that the core of the cold air will remain to the northeast of our region, temperatures will just be seasonably cool with continued dry weather with partly to mostly sunny skies (very much unlike last week's daily rains). Increased clouds and periods of rain are likely along this baroclinic zone, though most models show this staying mostly southwest of our region at least through Sunday.

 

Source: TropicalTidbits

 

Source: TropicalTidbits

 

Seasonable temperatures perhaps with relatively dry weather likely for early following week, with a possibly cooler and rainier weather later in week

 

The blocking pattern is likely to continue into the following week but likely without any true cold air to tap into, leading to relatively stable and seasonable temperatures with a rather weak temperature gradient typical of blocked patterns in spring. It could also continue to be dry if the baroclinic zone with unsettled weather just stays to the southwest of our region. But it is also possible that the baroclinic zone slowly pushes into our region, leading to increased clouds and showers the following Monday, though it will likely be weakening as it approaches and eventually fizzling out by Tuesday or Wednesday. Then, an upper-level trough moves into the western U.S. and could be strong enough for the associated storm over the Plains to push northeastward into our region later in the following week despite the blocking pattern, bringing an initial surge of modestly warmer air before it turns rainier and cooler as the storm moves slowly across the region. Days with increased clouds and rain are likely to be cooler just because of the lack of sun, not due to any cold air from higher latitudes, though somewhat chillier air could be brought in behind the storm with a possible upper-level ridge/trough in western/eastern North America setting up again leading to predominantly below average temperatures, though the core of it is likely to be to the southwest of our region (again, the opposite of March and the first half of April).

 

Source: TropicalTidbits

 

Mild to warm, humid, and unsettled week coming up with heaviest rain in northern areas, especially tonight into Monday, and warmest and drier weather in southern areas; sharply cooler late next Sunday into early following week before likely warmer and possibly unsettled again before drier end of April

Plain-language summary:

 

After a somewhat chilly weekend including a freeze last night, most of next week will be rather warm and unseasonably humid for April, especially in southern areas, though also relatively cloudy and unsettled with frequent rains, especially in northern areas. The most substantial rain will likely fall tonight into Monday, especially in northern areas, before it warms up. It cools down modestly in northern areas Tuesday through Thursday with a few rounds of lighter rains before widespread warmth likely with more sunshine dominates Friday and Saturday. After more rain Sunday, it turns sharply cooler for a couple of days, though it likely warms up again afterward, perhaps with more unsettled weather. It could turn drier for the end of April.

Meteorological discussion:

 

Except this morning, mild to warm spring weather to dominate for foreseeable future 

 

Although there are a few occasional chilly days, it is hardcore spring across the region now, with most days in the foreseeable future being mild to warm. This is due to (in addition to the normal progression of spring) a persistent upper-level ridge in the eastern U.S. downstream of a weaker upper-level trough in the western U.S. While there is still a surprising amount of cold arctic air across central and northern Canada, the arctic air masses are weakening quickly finally, and unlike in March, the upper-level ridge position near the U.S. East Coast (as opposed to in the central and southwest U.S. like in March), compounded by a still NAO unfavorable for intrusions of cold air southward into the U.S., will block most of the cold air from penetrating south into our region. Instead, it allows a persistent flow of warm, moist air from the Gulf of Mexico into our region, especially in southern areas, with unseasonably high dew points for a month typically characterized by low humidity outside of storm systems. Actually, it could be among the warmest Aprils on record for the contiguous U.S. after a stunning, record-breaking warm March.

 

Source: Climate Prediction Center

 

 

Mild to warm and unsettled with frequent rains through Thursday, with heaviest rain tonight into Monday, especially for northern areas; warmest and driest in southern areas 

 

That said, we are seeing a relatively chilly surface high-pressure system overhead this weekend that brought a freeze last night, but this is still nowhere near as cold as the arctic air masses in March. This air mass will quickly moderate through Monday as a low-pressure system tracks from the central Rockies to northern Quebec well to the northwest of our region and deep southwesterly flow brought on by the ridge mentioned in the previous paragraph takes over. The warm advection will initially lead to a period of rain, heavy at times in northern areas (>1" or 25 mm in many areas), tonight into Monday before the warm air actually reaches our region. But given all the moisture, it will be a relatively "dirty" warmup with some clouds (though also mixed with some sun outside organized storm systems), limiting just how warm it can get, especially in northern areas closer to the baroclinic zone. A cool surface high-pressure system to the north on Tuesday will sneak in cooler low-level air to northern areas, though this is far from an arctic air mass, and it will still be mild, just not warm. Two weak disturbances/elongated low-pressure systems will bring more rain, again heaviest in northern areas, Tuesday night to Wednesday and again on Thursday. The storminess is the result of being on the northern edge of the persistent warm, moist upper-level ridge across the eastern U.S.

 

Source: TropicalTidbits

 

More widespread warmth and sunshine Saturday before strong cold front brings more rain on Sunday, but likely minimal or no severe thunderstorms

 

The storminess exits on Friday, with the upper-level ridge expanding northward, leading to more widespread warmth with sunshine on Saturday ahead of a slow-moving cold front given the storm track well to the north and deep southerly to southwesterly flow. The amplification of the weather pattern is leading to the cold front being slow-moving, with one or possibly two low-pressure systems riding along the front. While the first one on Saturday will pass well to the northwest of our region, the second one is questionable, as it could be weaker, allowing the front to pass through on Sunday with a brief period of rain, or it could be stronger, allowing the front to slow down and leading to Sunday also being warm before a round of rain possibly heavy at times Sunday evening. A few rogue model runs even show precipitation lingering long enough behind the sharp cold front for precipitation to change to wet snow at the end, mostly for higher elevations, given the perfect setup, though I am skeptical. Either way, it will turn sharply colder behind the front. 

 

Source: TropicalTidbits

 

Before that, one or more days next week could feature temperatures above 77F (25C) in low-elevation locations, especially in southern areas. Although it will be an unsettled week with frequent rain chances, especially in northern areas, rain is unlikely to be heavy or persistent enough to cause flooding, especially given that the snow cover has already melted in almost all of our region, and it will likely be too cloudy to produce the instability necessary for all the severe thunderstorms that are expected over the U.S. Plains and Midwest.

 

Source: TropicalTidbits

 

Cooler for a couple of days early following week, though likely still seasonable to warm most days afterward and perhaps turning unsettled again before drier end of April

 

The upper-level ridge in the eastern U.S. weakens next weekend, and this will allow the strong cold front to at least briefly bring temperatures back below average, perhaps with a widespread freeze, by the following Monday. Still, the lack of any real upper-level troughing in the eastern U.S. and rapidly weakening arctic air masses suggest that any really cold air or snow is very unlikely. Yet another upper-level trough entering the western U.S. will likely pump the eastern U.S. ridge again later the following week, leading to more warm weather, though our region could be near the northern edge of the ridge again, leading to more clouds and rain. 

 

After that, the decreasing AO and NAO may push the jet stream farther south or promote the southern storm track across the central and southern U.S. to be stronger. This would lead to drier weather in our area with cool to mild (not arctic) southern Canadian high-pressure systems dominating our area and storms staying mainly to the south for the end of April. This is a weather pattern typical of El Niño and perhaps the first sign of the atmospheric pattern in our region responding to the developing El Niño. Given the strong April sun angle, daytime temperatures will be mild to warm with any sunny day given the lack of arctic air, though nighttime temperatures could still be cool with the dry air masses and clear skies allowing for good radiational cooling and large diurnal temperature swings. Such a pattern would also prevent unseasonably warm and moist air masses from reaching our region. Such air masses with no Gulf of Mexico moisture tend to be particularly dry at this time of year due to the lakes in eastern Canada being either frozen or quite cold and not providing much moisture to the air, and the still bare trees not transpiring moisture to the air either.

 

Source: TropicalTidbits

Rain, heavy at times today, then much colder Monday and Tuesday with narrow swath of snow from eastern Ontario to southern Maine; then rapid warmup through Thursday, followed by a few showers before temporarily cooler through Saturday; likely rather mellow and relatively warm afterward with rain chances

Plain-language summary: 

 

A storm very similar to Friday's storm will bring southerly winds followed by a period of rain, heavy at times, today before turning much colder for Monday and Tuesday. A swath of snow, locally heavy, is likely from eastern Ontario to southern Maine Monday night into Tuesday morning. After a cold Tuesday, it rapidly warms up through Thursday, before a cold front bring some showers and temporarily cooler air late Friday into Saturday. Despite some uncertainty afterward, the weather starting next weekend looks rather mellow and relatively warm though perhaps on the cloudier side with rain chances, though it could turn cooler later the following week.

 

Meteorological discussion: 

 

Today brings similar storm to Friday with southerly winds followed by a period of rain, heavy at times

 

It has been a rather active week across our region, though without the wintry precipitation that looked likely earlier due to the mid-week storm being stronger and tracking much farther north than previously expected, eliminating what was likely the last chance of widespread decent snowfall for our region. Instead, light rain fell for most before the warm front and most of the precipitation passed to the north, leading to southerly winds and warmer temperatures on Friday, except for Maine which remained more in the cold air, with northern areas receiving some ice pellets and freezing rain. Yet another similar storm is tracking through a similar region of central Quebec today, just two days later, with another round of southerly winds, but this time, with most of the rain (heavy at times) falling along the cold front.

 

Turns chilly Monday and Tuesday with snow likely from eastern Ontario to southern Maine, locally heavy in a narrow zone

 

Behind the cold front, a rather chilly though certainly not record cold air mass for early April will push into the region tonight into Monday, accompanied by some snow showers, especially in higher elevations, though accumulations will be none or minimal. This cooldown is occurring as the extreme upper-level ridge to the south and west that was dominant in March, causing many places to our southwest to experience the warmest March on record, is finally weakening, with broad temporary upper-level ridging in the western U.S. promoting an upper-level trough temporarily over eastern North America. A moisture-starved disturbance in the west-northwest flow will enter southern parts of the region, from eastern Ontario to southern Maine, Monday night into Tuesday. With the cold air in place, precipitation will fall as snow. Given that the disturbance is relatively weak and moisture-starved, precipitation will be much lighter and less widespread than with the storms this past week. However, it being April, the low-levels are warmer and more unstable than they would be for a cold air mass in the middle of winter, which will promote convective snow showers and bands that could bring locally heavy snow in a narrow area. 

 

Source: TropicalTidbits

 

Source: Climate Prediction Center

 

Cold Tuesday before quickly turning warmer through Thursday 

 

Unseasonably cold air will be reinforced behind the disturbance later Tuesday, but will not last long as an upper-level trough entering western Canada (-PNA) will promote some upper-level ridging in the eastern U.S. later in the week. The cold surface high-pressure system that will bring an unseasonably cold night Tuesday night will move southeastward into the western Atlantic later in the week, promoting southwesterly flow, sunshine, and quickly warming temperatures through Thursday. While the record heat of March to the southwest is gone, the persistent arctic air to the north during March, with parts of central and northern Canada experiencing the coldest March on record, is also weakening. This is leading to a large decrease in the temperature gradient and weakening of the baroclinic zone, with the wild March weather becoming much more mellow as we head deeper into April, in contrast to some other Aprils with wild weather. The continued positive NAO and AO also does not favor arctic air plunging southward deep into the U.S. 

 

Source: Patrick Duplessis and PRISM

 

Source: TropicalTidbits

 

Some showers likely late Thursday into Friday before temporarily cooler through Saturday, then likely mellow and relatively warm with occasional rain chances

 

A low-pressure system passing to the north will likely bring some showers late Thursday into Friday before briefly turning colder again behind a slow-moving cold front later Friday and Saturday, though the air mass does not appear especially cold like it did in March. Given the overall upper-level ridge in the eastern U.S. likely to be present for most of the following week, storms will likely track to the north or northwest of our region, leading to cooldowns being relatively brief and our region being in the warm sector of the storms, leading to mostly above average temperatures with rain likely along the warm and cold fronts. Unlike the warmups in March, the upper-level ridge axis near the U.S. East Coast favors a deep south-southwesterly flow of moisture from the Gulf of Mexico, likely leading to a "dirtier" warmup with more clouds and showers, especially in northern areas closer to the low-pressure track and baroclinic zone. However, if the upper-level ridge is weaker, that would allow for cold (even if not as cold as in March) surface high-pressure systems to sneak from the north and resist any real push of warmth, which would also lead to a farther south storm track that would bring longer-lasting periods of colder rain and cloudiness to our region. That is still a possibility, albeit not the most likely scenario, though that is a bit more likely later the following week as the AO becomes somewhat less positive and the eastern U.S. ridge weakens.

 

Source: TropicalTidbits

Milder and mostly dry today into Monday; then stormy through next weekend with rain except wintry mix in northern areas Tuesday into Tuesday night; potential big storm Thursday into Friday with snow changing to rain; milder with rain next weekend; then more typical April weather with occasional rain, lack of real cold, and little or no snow

Plain-language summary:

 

After being dry and unseasonably cold Friday and Saturday, it will turn milder but not particularly warm later today into Monday, with it remaining dry except light scattered snow showers mainly in northern areas. It will then be rather stormy through next weekend. Tuesday into Tuesday night will be rainy except a little snow to wintry mix possible in northern areas from central Quebec to northern Maine. It will turn cooler and drier on Wednesday before a widespread potentially big storm bringing snow to wintry mix to rain occurs late Thursday into Friday, with the best chance of a big snowstorm from central Quebec to northern Maine. It then turns warmer with rain next weekend before it turns cooler, but without much if any arctic air to the north to tap into, leading to a more typical April weather pattern with occasional rain chances but likely little if any snow especially at lower elevations.

 

Meteorological discussion:

 

Milder but not particularly warm later today into Monday but staying mainly dry; rain to south and wintry mix to north on Tuesday

 

March has been characterized by a huge temperature contrast between persistent arctic air over central and northern Canada and record-breaking heat in the western and central U.S. This persistent temperature contrast is characterized by a -PNA, +AO, and +NAO, virtually the opposite of most of the past winter. This battle will continue for the next week and play a key role in the weather in our region. The largely dry arctic air mass of Friday and Saturday is moving out with little or no precipitation except light scattered snow showers in northern areas with little or no accumulation. This fits the theme of the winter of it being difficult to ram rich Gulf of Mexico or Atlantic moisture into the cold air masses in our region. Dry southwesterly flow will bring milder air later today into Monday, with a weak surface low-pressure system passing to the north on Monday carrying its precipitation mainly north of our region. The warmer air will fall well short of the incredibly warm temperatures to our southwest. A cold front will pass Monday night, and arctic air will try to push in again, but like most of this month, the upper-level ridge to the south will be too strong for the cold front to advance much, with the ridge actually centered over the southeast U.S. instead of farther west like last week. Therefore, the front will stall over our region as another somewhat stronger but elongated, more moisture-rich low-pressure system advances from the west. With an arctic surface high-pressure to the north over northern Quebec and the surface low-pressure system passing through our region, widespread precipitation will occur on Tuesday and Tuesday night, mainly as rain for most of the region given that the cold air is not really able to advance southward much before the precipitation arrives. However, northern areas deeper into the cold air, from central Quebec to northern Maine, could receive a bit of snow changing to a wintry mix of ice pellets, freezing rain, and rain. Low-level cold air channeled southwestward through the St. Lawrence Valley could lead to freezing rain there especially near Quebec City. Southern areas from southern Vermont to southern Maine will get into the warm sector, with temperatures surging above 60F (16C) for a brief time.

 

Source: TropicalTidbits

 

 

Source: Climate Prediction Center

 

 

Cool, dry Wednesday, then potential big storm with snow to wintry mix to rain late Thursday into Friday, perhaps last widespread snow of season 

 

The low-pressure system will move out by Wednesday, with another arctic surface high-pressure system pushing in with colder and drier air. But once again, the upper-level ridge to the south will remain strong, while some upper-level troughs and storminess finally reaches the western U.S. after being baked in dryness and record warmth for the past few weeks. One disturbance will be moving eastward through the Plains and U.S. Midwest on Thursday, and eventually reaching our region Thursday night into Friday. With the arctic air able to push a bit farther south this time and still being relatively fresh ahead of the storm, precipitation will likely at least start as snow for most of the region, perhaps except for far southern areas, though this will depend on the exact storm track which has been trending northward lately, perhaps a testament to the strength of the upper-level ridge to the south. This might be one of the few times this cold season in which rich Gulf of Mexico moisture is rammed straight into a fresh cold air mass cold enough for snow, with the surface high-pressure to the north and northeast providing low-level cold air (albeit not as strong as in winter given that it will be April) for the warm, moist Gulf of Mexico air to overrun aloft. There is remarkable agreement (for 4-5 days out) on a scenario like this occurring. As a result, precipitation could be rather heavy, and someone could receive a lot of snow, perhaps one of the biggest of the season. That said, the relatively warm temperatures (warmer than -8C) through a deep layer of the lower-troposphere will not favor ideal dendrite formation and favors riming that leads to lower snow-to-liquid ratios and wetter snow, limiting snow depth. Areas south of a line from Ottawa to Montreal to Bangor, Maine will likely change to ice pellets and then a cold rain by Friday, unless the storm track goes farther south than currently shown. For now, the best chance of a big snowstorm is from central Quebec to northern Maine. This could be the last widespread snowfall of the season for our region.

 

Source: TropicalTidbits

 

 

Warmer with rain next weekend, then cooler but likely lack of arctic cold and more typical April weather pattern with occasional rain chances

 

Another stronger storm will follow closely behind with an almost closed off upper-level low approaching the region next weekend. By this time, the cold air will have become stale, and the strength of the storm combined with is track well north of our region into northern Quebec will likely ensure precipitation will fall as rain for everywhere in our region with warmer air arriving. Cooler and drier air comes in behind the storm, but by this time, the supply of arctic air to the north appears to finally weaken in earnest, and yet the upper-level ridge to the southwest of our region will have weakened. This will reduce the temperature contrast and yield a more typical early-mid spring weather pattern, with mostly mild days and occasional temperature swings and storminess but without the big temperature contrasts, and any snowfall likely being at most sporadic and mostly at higher elevations. 

 

Source: TropicalTidbits

 

First real taste of spring through Tuesday; major storm brings wintry mix, rain, and warmth Wednesday and early Thursday; back to winter with unseasonable cold late Thursday into next week with snow likely Friday-Friday night and following Monday

Plain-language summary:

 

It will be very mild through Tuesday, marking the first true taste of spring for our region. Then, it will turn colder in northern areas as a major storm bring ice pellets and freezing rain to northern areas Wednesday into early Thursday, while southern areas stay very warm with some rain. A brief period of heavy showers or even a thunderstorm is possible early Thursday before turning much colder, possibly accompanied by a little snow. Winter weather will likely then dominate for at least a week, albeit the March sun angle will make the cold less intense but could also make any storms stronger with stronger dynamics and more moisture. Snow is likely, especially in northern areas, late Friday into Friday night, with a bigger storm possible the following Monday. It remains very cold for March afterward but perhaps drier before possibly turning milder later the following week.

 

Meteorological discussion: 

 

Very mild and mostly dry through Tuesday

 

Right after the calendar flipped to March, the weather pattern has flipped completely from the cold, suppressive wintertime weather pattern, sort of like last year. A +EPO, +NAO, and +AO has scoured the arctic air out of the contiguous U.S. and southern Canada with an active storm track to the north leading to persistent mild westerly to southwesterly flow of Pacific or even Gulf of Mexico air. The upper-level trough in western North America (-PNA, rare this winter even if relatively modest) has also boosted the eastern North American upper-level ridge, with rain falling deep into Quebec yesterday with a storm tracking way to the north. Even the cold front behind it will only briefly turn the winds to northerly, and the air mass will still be warmer than average for this time of year. Southeast of the Appalachians, sunshine and downsloping westerly winds will actually make it warmer than yesterday, when that area was stuck in low-level cold air damming. Another clipper tracking well to the north on Monday will back the flow to southwesterly again, leading to Monday being even warmer with many lower elevation locations, especially in southern areas, reaching 60F (16C) or higher in lower elevations given the higher March sun angle, melting and degrading snow cover, and unseasonably warm air mass and upper-level ridging, and it will be dry as well.

 

Source: TropicalTidbits

 

Source: Climate Prediction Center

 

Low-level arctic air bleeds into northern areas with major storm Wednesday and early Thursday leading to ice pellets and freezing rain in northern areas, continued warmth and some rain in southern areas, possibly ending as a little snow everywhere

 

At the same time, a very cold arctic air mass will be pushing across central and eastern Canada on Tuesday and Wednesday behind the clipper's cold front, but like last week's arctic air mass, it will not be able to push south much due to resistance from the strong upper-level ridge. The front will be almost stationary as another elongated disturbance entering the northwestern U.S. will ride along the front. After a mild Tuesday, the front will slowly push through Northern Maine and areas north of the U.S./Canada border, allowing the low-level cold air to bleed in starting later Tuesday with northerly to northeasterly flow. The low-level cold air will be enhanced by terrain-induced channeling along the St. Lawrence Valley and even the Champlain Valley initially. However, areas to the south will get even warmer, possibly even breaking some daily records, and it will remain warm aloft everywhere due to the upper-level ridge. 

 

The disturbance from the west will strengthen into a formidable storm in the Great Lakes on Wednesday, especially as it at least partially phases with and picks up a cut-off upper-level low in the southwestern U.S. This interaction has been a difficulty for models to predict, with models initially showing this phase creating a very strong storm cutting northwest of our region, then a couple of days ago showing a much flatter northwestern U.S. disturbance that does not phase with the cut-off low, leading to a weaker, farther south, and colder storm, and now the models have reverted back to at least a partial phase. Given the low-level cold air in northern areas, precipitation will likely at least start as ice pellets and/or freezing rain, possibly heavy at times, while southern areas will stay just rain, possibly south of the main precipitation shield. Some areas could see a real ice storm, most likely in eastern Ontario and southern Quebec and possibly parts of Maine, if the storm is more elongated, which would allow for the heavy precipitation and precipitation types to train over the same area as opposed to a stronger storm that would push everything north with time with stronger warm advection. If the storm is farther north and stronger, the unseasonable warmth will push into all of our region at least briefly, possibly with a dry slot, followed by a sharp cold front with a brief period of heavy showers or even a thunderstorm early on Thursday before turning much colder, perhaps with a brief period of light snow depending on how much energy is left dangling to the southwest of the main storm. Usually, such scenarios with a strong storm tracking to the north do not favor backside snow, especially in recent years. If the storm is farther south and weaker, wintry precipitation will continue for a full day in northern areas with a constant supply of low-level cold air from the northeast until the storm exits on Thursday. As I wrote in my blog post a week ago, it is ironic that the region was struggling to get good moisture with all the suppression, but now the suppression suddenly breaks and now the upper-level ridge is too strong for snow in most or all of our region.

 

Source: TropicalTidbits

 

Old model runs showing alternative scenarios. Source: TropicalTidbits

 

Winter returns late Thursday, snow likely Friday into Friday night especially in northern areas and major storm possible Monday

 

The flip back to winter weather is powered by the return of the western North American ridge (+PNA) and a weakening of the Pacific jet, though interestingly, the AO and NAO are expected to remain positive, so there will not be any appreciable blocking or push of arctic air deep into the southern U.S. This will maintain a stronger than the already typically strong temperature gradient at this time of year, acting as fuel for storms especially with the lower springtime stability. As such, the active weather pattern will continue afterward, with another clipper already approaching our region from the west-northwest on Friday. This clipper appears stronger than most from mid-winter, perhaps powered by the March sun angle making the air masses less stable and strengthening the warm air masses to the south clashing with the arctic air to the north. Given the cold air, albeit modified by the March sun angle, precipitation will fall as snow throughout the region at least initially later Friday, possibly mixing with and changing to scattered showers south of the storm track Friday night as warm advection occurs again. Given the dynamics, the favored locations north of the storm track could get rather heavy snow for several hours. The trajectory and strength are still in question this far out, but right now, it appears that the heaviest snow will likely target northern areas. 

 

Another arctic air mass follows behind it before another disturbance riding along the temperature gradient has the potential to become a big storm, colder than this upcoming week's storm, depending on how amplified the weather pattern is. The position of the broad upper-level trough axis to our west puts our region in a favorable spot for cyclogenesis and moisture transport from the south straight into the arctic air, something not seen often this winter. It has the potential to finally be a widespread big snowstorm, especially given the strengthening warm and humid air masses in March pushing into the storm, but it could very well be too weak and suppressed like most of this winter, or even too amplified and going too far north, leading to a change to rain.  

 

Source: TropicalTidbits

 

Staying unseasonably cold for March through most of following week, possibly drier mid-late week and then milder

 

After that, the upper-level ridge/trough pattern appears to shift east, with the upper-level trough axis pushing east of our region later the following week, likely leading to drier weather but perhaps still unseasonably cold for March. Throughout much of this period, highs could be at or below freezing on most days, with the occasional night at or below 5F (-15C), more typical of January or February. However, the lack of -AO or -NAO high-latitude blocking suggests we could see a warmup as well with dry west-southwesterly flow from the Rockies, which will likely be unseasonably warm by then, but it remains to be seen how much resistance the arctic air will provide in our region, especially given the abundant arctic air projected to remain across Canada.

 

Source: TropicalTidbits

 

Very cold through Monday, then turning milder through Thursday with a little snow in southern areas Tuesday night into Wednesday; potential wintry mix Thursday night into Friday before warm next weekend into following week; then turning stormier and then colder

Plain-language summary:

 

After being very cold through Monday, it will turn milder, yet for most, the transition period will fail to produce much snow like such periods often do. Instead, it will be mostly dry through Thursday except a little snow from southern Vermont to southern Maine Tuesday night into Wednesday. Shallow cold air will lead to one last chance of wintry precipitation Thursday night into Friday, though it is more likely to be freezing rain than snow. It then turns warm through following week with frequent rain chances, though any day that does turn sunny could be exceptionally warm for March. Northern areas may still have the risk for wintry mix or freezing rain depending on the exact configuration of the weather pattern. It will likely turn stormier and than colder for mid-March, possibly with snow returning. 

 

Meteorological discussion:

 

Very cold Arctic air through Monday, then milder with light snow in southern Vermont to southern Maine Tuesday night into Wednesday while it stays dry to the north 

 

After a brief thaw yesterday, a very cold Arctic air mass directly from the north with no modification will likely bring the last sub-0F (-18C) night of the winter tonight as surface high-pressure crests overhead leading to an ideal radiational cooling setup of light wind, clear sky, dry air, and deep snow cover. Afterward, the arctic surface high-pressure will move offshore the U.S. East Coast, and a series of elongated clippers will pass to the north next week. Both of these combined will lead to a warming southwesterly flow aided by a stronger March sun. An almost closed-off upper-level low will enter the western U.S. on Monday, with weak pieces running out ahead of the main upper-level low that will produce light warm advection snow in southern Vermont to southern Maine later Tuesday into Tuesday night. This southern jet disturbance has a decent amount of moisture, and if the prevailing jet pattern had been more amplified, especially with the polar jet upper-level trough being stronger and phasing with and picking up the southern jet disturbance, this could have been a much bigger snowstorm like models had shown a few days ago. However, this will be yet another potential bigger storm that mostly fails to materialize. The northern upper-level trough is very flat and is not digging far enough south nor in the right position to pick up the juicier southern disturbance, leading to a very stretched out and suppressed disturbance with relatively weak forcing and precipitation at any one location yet again. Central Maine could get the jackpot with locally up to 4" (10 cm). Areas from the U.S./Canada border on northwestward will stay dry in between the clipper passing to the north and the stretched out southern disturbance to the south Tuesday night into Wednesday, though everyone will turn milder and see increasing clouds.

 

Source: TropicalTidbits

 

Transition period to warmer weather mostly fails to produce wintry precipitation except one last iffy chance Thursday night into Friday

 

Afterward, the weather pattern will change dramatically, powered by a much stronger Pacific jet (+EPO), +NAO, +AO, and -PNA. This change will not only scour the arctic air from the contiguous U.S., but also force upper-level troughing in western North America that further promotes a ridge in eastern North America and western Atlantic and a storm track way to the north. It is ironic that we had so much potential for storminess and snowiness from a temperature battleground over the past month, yet the weather pattern ended up being repeatedly too suppressive, and now, it will simply flip 180 degrees to having way too strong of a ridge for snow in our region, especially in southern areas, after next Friday. It has been an incredible waste of potential for big snowstorms; it just needed to be in between the suppressive and ridge-dominated patterns. Even the transition period from cold to warm pattern, which usually produces a decent snowfall, appears to mostly fail to produce much if any snow for most. 

 

Source: Climate Prediction Center

 

However, there is still one last slight chance for snow for northern and eastern parts of the region next Friday. On Thursday, an arctic surface high-pressure will press southward just slightly, barely penetrating south of the U.S./Canada border, behind a stalling cold front from the previous weakening clipper passing to our north on Wednesday. Meanwhile, the main upper-level low, though weakening, will finally push northeastward into our region as another upper-level trough into the western U.S., pumping the eastern U.S. ridge and leading to southwesterly flow aloft. This flow of warm, moist air from the Gulf of Mexico will ram into the shallow arctic air in northern and eastern parts of our region, leading to possibly heavy precipitation Thursday night into Friday. Most models indicate that the arctic air, although is very cold, will mostly stay just north of our region and is so tenuous and shallow with above freezing temperatures persisting aloft for most of the region except Maine, where cold air damming will help block the surge of warmer air. But if the cold air can press in more, and the upper-level low is timed perfectly to arrive just as the cold air is coming in (not too early, before the cold moves in, and not too late, after the cold is about to leave), it could be just cold enough for a more widespread wet snow. Most likely, the cold air will be shallow and dammed against the Appalachians and channeled southwestward through the St. Lawrence Valley, leading to freezing rain, and icing could be substantial for some given the strength of the shallow arctic air. The system could also be weaker, resulting in little precipitation, especially if more of the energy gets pulled out Tuesday night into Wednesday ahead of the main upper-level low.

 

Source: TropicalTidbits

 

Warm next weekend through following week with frequent rain chances, maybe still wintry precipitation chances in northern areas

  

Despite the low-level arctic air that will be initially difficult to scour out, eventually, the next upper-level trough will promote a storm track well to our north next weekend, leading to the arctic air retreating well to the north, warming temperatures, and some rain. A blowtorch for most of our region is likely at some point between next weekend and the following week given the strength of the upper-level ridge, with several storms tracking well to our north and warm southerly flow blasting into our region. Temperatures could exceed 70F (21C) in lower elevations if there is enough sunshine! Occasional cool downs behind storms could occur, but the air masses will not be very cold. Even the feedbacks of frozen Great Lakes and deep snow cover will be no match for the strength of this ridge, and the warmth will obliterate the snowpack. Even if the ridge is weaker than modeled like has been the case for the past month, it will likely not be enough to change this general narrative. Unless it turns very cold again in mid-late March, it will be the 6th warmer than average March in a row. Given the warm, moist Gulf of Mexico air involved, there could be heavy rain at times depending on the storm track, especially along cold warm fronts, but the storm track could be so far north that the best dynamics and heaviest rain stays to our northwest, especially next weekend. Still, it will likely not be a "clean" warm-up with dry weather and sunshine, perhaps except next Sunday and following Monday, which is rare this early in the spring anyway, especially in northern areas. Such warm air masses traversing over snow cover and cold ground usually lead to a lot of low clouds and fog especially initially with the warm advection, and this could be amplified with the progression of storms and repeated fronts. If the overall upper-level trough/ridge pattern in western/eastern North America is a little weaker, there could be sneaky surface arctic high-pressure systems well to the north that lead to much cooler surface temperatures, especially in northern areas, while it stays warm aloft, a recipe for low clouds and even a wintry mix or freezing rain if the storm track is close enough.

 

Source: TropicalTidbits

 

Source: TropicalTidbits

 

Cold air likely to return at end of following week, possibly with storminess and even return of snow

 

Models are also in good agreement that the upper-level ridge will gradually weaken towards the end of the following week, and with the Pacific jet weakening, arctic air is likely to make a comeback across southern Canada and northern U.S., initially to our west but eventually spreading eastward for mid-March. In the transition period, it could be quite stormy, with warmth and heavy rain and possibly even thunderstorms. But it is possible that as the cold air and baroclinic zone slowly pushes southeastward that there is one or two storms that spin up along it in which our region is on the cold side, leading to snow. It is almost always difficult to get a big snowstorm from rain changing to snow, as usually the cold air needs to be established first, but in such an amplified weather pattern, it is plausible even if not very likely. It will be mid-March with an obliteration of the snowpack, so any cold air will not be nearly as strong as we have seen over the past month, but it could still be cold enough for snowfall, and if the weather pattern is less suppressive as it usually is later in March as the jet stream climatologically moves northward, and it becomes easier to tap into the strengthening warm, moist air masses in the southern U.S., the potential for bigger storms still exists. Of course, with averages rapidly climbing, it will be more difficult to keep precipitation as snow, but it is certainly still possible through early April.

 

Source: TropicalTidbits