Amazingly persistent drought to continue; unseasonably warm through Tuesday, then much cooler for a few days with frost/freeze for many, then back to unseasonably warm next weekend into following week while staying dry; likely cooldown with some rain for mid-October

Plain-language summary:

 

It will be unseasonably warm across the region through Tuesday, though with little or no humidity and no rain. It will then turn much cooler with frost and freezes likely for many Wednesday and Thursday nights, while remaining dry and sunny. It then warms back up to unseasonably warm temperatures for next weekend through the following week while staying dry, before likely turning cooler for mid-October at least temporarily, accompanied by some rain.

 

Meteorological discussion: 

 

Unseasonably warm through Tuesday, then much cooler with frost and freeze for many Wednesday and Thursday nights, still dry and relatively sunny 

 

It is unseasonably warm across the region, though not record warm, as strong upper-level ridging dominates in central and eastern Canada, like most of the past two months. It will also be quite warm on Monday before a rather strong cold front brings a shot of cool, dry air straight out of the north later on Tuesday, with it still being rather warm on Tuesday southeast of the Appalachians with the later arrival of the front there. Once again, like most of the past two months, the dry westerly to west-northwesterly flow with no access to Gulf of Mexico or western Atlantic moisture will lead to no rain (just some mid to high-level clouds) with the cold front. Thursday's rainstorm for most and widely scattered showers on Friday is likely the last rain for another 10 days or more! Behind the cold front, another huge Canadian surface high-pressure system will move southeastward into our region and dominate for several days afterward. Even though the core of the cold air will once again stay off to the northeast, the chilly and dry air mass, combined with the drought leading to little or no evapotranspiration of moisture from the ground into the atmosphere, will lead to a widespread frost or freeze Wednesday and possibly Thursday nights outside of the wider St. Lawrence and Champlain Valleys as well as urban areas and areas close to large bodies of water. However, with the average temperatures rapidly falling, the frost and freeze could be more widespread than the frost and freeze event of last weekend, with even parts of the St. Lawrence and Champlain Valleys possibly at risk, though that is not that unusual for the beginning of October.

 

Source: TropicalTidbits

 

 

Turning back warmer next weekend into following week while remaining dry, then possibly cooler for mid-October with at least some rain 

 

The surface high-pressure system will eventually move to our southeast by next weekend, leading to the northerly flow gradually switching to a warmer and persistent west to southwest flow, will still remaining dry and mostly sunny, with the drought resuming intensification after last Thursday's rainstorm. Temperatures will also become unseasonably warm as an upper-level trough digs into the western U.S. (PNA turning negative) promoting a downstream upper-level ridge and warm southwest flow in eastern North America. The +NAO and slightly positive AO associated lack of high-latitude blocking will promote a rather zonal jet stream that does not allow any Arctic air to push southward into our region. The huge high-pressure system will also block both Hurricanes Humberto and Imelda from reaching anywhere north of the southeast or mid-Atlantic U.S., keeping our region dry. Incredibly, the weather looks to be quite monotonic, with warm, dry, and sunny weather with little wind for possibly an entire week! However, there are signs that a bit of upper-level ridging will replace the previous upper-level trough in the western U.S. just before mid-October, which would lead to more upper-level troughing and cooler weather in our region, with perhaps finally some rain to accompany the transition to cooler weather. However, this is beyond 10 days out, so confidence is low, and the latest model runs have suggested that this change might be relatively short-lived.

 

Source: TropicalTidbits

 

 

Source: Climate Prediction Center

 

 

Source: TropicalTidbits

 

Quick warm up through Monday and turning breezier, then cloudier with light rain late Monday into Tuesday; uncertain potential for more rain especially in southern areas Thursday and Friday; cool and dry again next Sunday before warming back up, with drought likely to resume intensifying

Plain-language summary:

 

After an unseasonably chilly air mass for the past 1-2 days with frosts and freezes in normally colder locations, it will quickly warm up through Monday before turning cloudier with light rain late Monday into Tuesday. It will be mostly dry on Wednesday, but with some remaining cloud cover, with rain likely on Thursday and Friday, especially south of the U.S./Canada border, though this is still a bit uncertain. It will turn dry, clear, and cool again on Sunday before warming back up, but not turning hot, for the following week, with the dry weather leading to the drought intensification resuming.

 

Meteorological discussion:

Unseasonably cool air mass to quickly moderate through Monday, then light rain late Monday into Tuesday 

 

An unseasonably cool and dry air mass directly from the north pushed into our region yesterday associated with a cool and very dry Canadian surface high-pressure system, resulting in frost and freezes for many locations outside the broader valleys like the St. Lawrence and Champlain Valleys as well as away from large bodies of water. The Maniwaki sounding yesterday evening showed that the air mass was actually the driest on record for this date, with a precipitable water of only 0.25" (6.4 mm). The drought is also helping nights turn chilly with the ground not adding any moisture into the air to slow the cool down. However, the high-pressure system is quickly moving off to the east, with strengthening southerly flow on the back side leading to a quick warmup through Monday. It will also turn cloudier and breezier (in contrast to the mostly calm winds recently) as a disturbance approaches our region from the Great Lakes, and the disturbance will actually bring at least scattered light rain late Monday into Tuesday, the first rain in more than 2 weeks for many locations. As has been the case for the past 2 months though, the extremely dry antecedent air and lack of time to sufficiently advect Gulf of Mexico or western Atlantic moisture into the region mean that rainfall amounts will be relatively light.

 

Source: Storm Prediction Center

 

Source: PivotalWeather

 

Source: TropicalTidbits

 

Complicated weather pattern with more clouds this week and rain likely Thursday and Friday especially south of U.S./Canada border 

 

It is a somewhat complicated or uncertain weather setup next week, with actually several days of potential rainfall, especially south of the U.S./Canada border. Although the disturbance mentioned earlier will push off to our east by Wednesday, another disturbance lagging behind to the west over the Midwest U.S. will actually be slightly cut-off from the main flow and meander through the central and eastern U.S., with upper-level and surface ridging building overtop of it to the north. As is always the case with cut-off lows, the timing and track of the system is still rather uncertain. If it is a little farther north, feels more of the mid-latitude jet stream to the north, and the jet stream is configured to have west-southwest flow over our region, the cut-off low could push northeast into our region and bring widespread light to moderate rain Thursday into Friday. On the other hand, if it is a little farther south, or the mid-latitude jet stream to the north is configured to bring a west-northwest flow suppressing the system farther south, then the system could move more slowly and miss our region to the south entirely with its closest approach Friday into Saturday, which would be a missed opportunity to dent the intensifying drought, though the systems would almost undoubtedly lead to a cloudier week overall than for most of the past 2 months. Today, models are in better agreement on the first, rainier scenario, but it is still too early to have high confidence on this.

 

Source: TropicalTidbits

 

Source: TropicalTidbits

 

 

Dry, clear, and cool again next Sunday before warming up but not turning hot, with drought intensification likely resuming 

 

Regardless of what happens with the cut-off low, there is good model agreement on another dry, chilly Canadian surface high-pressure system sneaking in next Sunday, though the cold air will not penetrate very far south, and the bulk of it could stay to our north. Like with this weekend's cool shot, nighttime frosts and freezes are possible for many locations before the high-pressure system pushes to the east, allowing for a warming trend for the following week. However, with the rapidly lowering sun angle and average temperatures, these future warmups will become less and less likely to yield summerlike temperatures and especially humidity. Still, with the mean upper-level trough axis continuing to be near the North American West Coast leading to a downstream broad upper-level ridge over central and eastern Canada, temperatures will likely be above average most of the time, though this pattern also allows for occasional dry, chilly Canadian surface high-pressure systems to favor frost and freezes for normally colder locations, like this weekend and next weekend and possibly later the following week, especially with the ongoing drought. The teleconnections do not yield any strong signals, though the slightly positive NAO and AO favors a rather zonal jet stream to the north blocking cold arctic air from reaching the entire contiguous U.S. and southern Canada, which matches ensemble projections of widespread warmth from West Coast to East Coast. However, this is a bit uncertain in the long-range, as models have occasionally shown bigger cooldowns in eastern North America perhaps associated with a slightly more positive PNA promoting more upper-level troughing in eastern North America. Also, the models, especially the ECMWF model, have underestimated the intensity of the cooldowns over the past 2 months in the long-range. Still, our location generally to the east of the upper-level ridge axis and west of the upper-level trough axis is also likely to promote sinking air and dry weather most of the time through early October, intensifying the drought further, even with the seasonal cooldown leading to lower evaporation rates.

 

Source: TropicalTidbits

 

 

Source: Climate Prediction Center

 

Dry for perhaps 10 more days with intensifying drought before possibly at least temporarily turning a little wetter; gradually warming up through Thursday with sunny skies and low humidity, then cools down again before warming back up for following week

Plain-language summary:

 

After a few light scattered showers today, it will dry out again, with dry and mostly sunny conditions expected through Thursday with a gradual warmup. Thursday and Friday could feature summerlike daytime heat, though with low humidity and cool nights. It will then cool down substantially, still with not much rain, for a few days before warming back up for the following week, with most days being warmer than average, especially during the daytime. Little rain is expected over the next 10 days, with the drought continuing to intensify, before possibly turning wetter at least temporarily, though it is unlikely to mark a shift to a longer-term wetter weather pattern yet.

 

Meteorological discussion: 

 

Dry and sunny with gradual warmup through Thursday

 

A very weak disturbance/cold front is passing through today, with just some increased clouds earlier today. A few days ago, some models showed there being an upper-level low bringing more substantial rain, but instead, it is a much weaker and stretched out disturbance. Both dynamics and moisture lacking (there is no moisture flow from the Gulf of Mexico or western Atlantic), with almost no rain falling and reaching the ground anywhere. Another broad Canadian surface high-pressure system is moving into our region, with slightly cooler air directly from the north, but it has no access to real cold air with only a weak temperature gradient. 

 

Upper-level troughing moving into the western U.S. in the next day or two will promote the already dominant upper-level ridge across Canada to focus its strength in eastern North America instead of farther west, where it has been most of the time over the past few weeks. This is despite a +PNA that is continuing, but likely, the +PNA is powered by the intense ridging still present in western and central Canada instead of the western U.S. The -NAO is also associated with the ridge being centered at a rather high latitude over Quebec, with a very weak cut-off low to the south over the coastal southeast U.S., leading to a slow-moving blocking pattern. The eastward expansion of the ridge will cause dry, sunny weather to continue in our region but with a gradual warmup muted by the lower September sun angle but aided by the very dry ground leading to all of the sun's energy going to heating the ground instead of evaporating ground moisture. Daytime temperatures will reach summerlike levels, with highs exceeding 80F (27C) on Wednesday and Thursday in lower elevation locations. It would have been even hotter if there had not been the coastal upper-level low that is a bit close, weakening the westerly flow of hotter air. Once again, the westerly flow will not allow for any Gulf of Mexico or western Atlantic moisture, leading to relatively low dew points and still cool nights.

 

Source: TropicalTidbits

 

 

Source: Climate Prediction Center

 

 

Stronger cold front Thursday night with little rain expected, cooler afterward and remaining dry for at least a few more days before possibly turning wetter

 

A stronger cold front will push into our region directly from the north Thursday night or around that time, beating down the upper-level ridge in our region somewhat. Once again, the upper-level disturbance responsible for the cold front will be mostly to the northeast, leading to our position being in the dry side of the upper-level wave train, especially with no Gulf of Mexico or western Atlantic moisture. There is still some time for the overall configuration to change, but it appears unlikely again for anything more than a few light showers from this front. Another stronger, cooler Canadian surface high-pressure system will establish itself over Quebec next weekend and may transition into a cut-off upper-level ridge, leading to more dry weather. The surface high-pressure will eventually move to the east, leading to the cool air mass modifying and a gradual warmup through the middle of the following week as upper-level ridging builds back into our region, though it will likely not get as warm as this upcoming Wednesday and Thursday. With all this dry, sunny, and mostly warm weather over the next 10 days promoting rapid evaporation of what little ground moisture there is left, the drought will continue to intensify. After that, it is not clear if the high-pressure system will continue to sit over our region, blocking any storms from reaching our region for another several days or more into the following week, or if the high-pressure system will push far enough to the northeast for some storminess slowing approaching from the U.S. Plains to throw in more clouds, moisture, and eventually rain into our region. The storminess could also just weaken, leading to cloudier skies but only light rains. Upper-level ridging appears to be dominant in eastern Canada through the end of September, which will likely any wetter period temporary.

 

Source: TropicalTidbits

 

 

Source: TropicalTidbits

 

 

Source: U.S. Drought Monitor and Canadian Drought Monitor

 

Dry weather returns for extended period; cool through Tuesday, then modest warmup through Thursday, then cooler again Friday before gradual warming through following week while staying mostly dry and sunny with low humidity leading to worsening drought

Plain-language summary:

 

After rain over the past few days dented the drought slightly, the dry weather pattern has returned today. It also has turned much cooler and will stay cool through Tuesday. It will warm up modestly Wednesday and Thursday before a reinforcing cool shot arrives by Friday, with light showers possible immediately before the reinforcing cool shot. It will then likely warm up for a longer period of time afterward, but never getting truly hot, while remaining mostly dry and sunny with cool nights and the drought worsening again.

 

Meteorological discussion: 

 

Dry weather returns, unseasonably cool through Tuesday, then modest warmup through Thursday

 

After many areas received the most rain in over a month over the past few days, dry weather has returned today, except for isolated showers mostly over higher terrain. It is also unseasonably cool with an amplified pattern across North America consisting of a pronounced upper-level ridge bringing record high temperatures to western Canada and a deep upper-level trough in Quebec. The cold air is not be as pronounced in our region as in the Midwest U.S. due to the trajectory of the cold air first going into the Midwest U.S. and then getting modified as it moves east into our region, as opposed to coming directly from the north or northwest. However, on Monday, as the upper-level trough weakens as pulls to the northeast, a Canadian surface high-pressure system will approach, briefly turning the flow slightly more to the northwest for a more direct shot of cold air into our region, though the truly cold air will still stay to the north of our region. The clouds and isolated showers will also mostly go away by Monday as the surface high-pressure system takes over. It will then warm up modestly through Thursday while staying sunny and dry as the surface high-pressure system moves just to our south, allowing modest warm advection from the southwest.

 

Source: TropicalTidbits

 

 

Cooler again Friday, then gradual warming through following week while not getting truly hot and remaining dry and sunny with cool nights and worsening drought 

 

The weather pattern afterward looks to resemble that of August in many ways, with some upper-level troughing pushing into western North America leading to a downstream upper-level ridge in central and eastern North America, but with the ridge axis staying west of the East Coast. Like with the amplified weather pattern earlier this week, this new weather pattern will also be phase shifted from the typical PNA, NAO, and AO patterns, rendering only weak signals on those indices. This weather pattern will be characterized by repeated Canadian surface high-pressure systems moving into our region, with the associated dry air and descent precluding thunderstorms or even any rain and clouds for the most part, leading to the drought continuing to progress after the recent rains temporarily dented it a bit. There may be occasional rain chances associated with cold fronts coming from the north, but the deep west to northwesterly flow preventing any moisture from the Gulf of Mexico from entering into our region, and the generally unfavorable location east of the upper-level ridge axis and west of the upper-level trough axis. 

 

Source: Climate Prediction Center

 

 

One of these cold fronts will come late on Thursday, with a reinforcing cool shot afterward, but then the air mass will gradually warm as the upper-level ridge gets more firmly established over the central and eastern North America. There also won't be any strong westerly or southwesterly flow for strong warmth and moisture advection, and with the lowering sun angle in September, the warmup will be gradual, and it is unlikely to become truly hot again, even with the drought leading to more of the sun's energy going into warming the ground instead of evaporating moisture. Nights will also remain relatively cool with a larger than average day-to-night temperature difference, like in August, due to the clear skies, light winds, dry air, and lengthening nights allowing for good nighttime radiational cooling.

 

Source: TropicalTidbits

 

 

One possible caveat is that today, a few models (e.g. ECMWF, UKMET, and ICON) show a cut-off low diving southward underneath what would otherwise be broad upper-level ridging across central and eastern North America. This would lead to a couple of days of cloudier and more showery weather, at least delaying if not stopping most of the warmup. However, models tend to show this more than in reality, and other models are not on board with this.

 

Source: TropicalTidbits