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