Record warmth through Monday before sharp cold front brings rain later Tuesday; frost/freeze Wednesday and Thursday nights, then warms up again while staying dry through middle of following week; then perhaps more typical up-and-down temperature pattern

Plain-language summary:

 

Record warmth and sunshine, more typical of mid-summer, will dominate the region today and Monday. The warmth will abruptly end later Tuesday with rain before turning much cooler and dry again on Wednesday. Widespread frost and freezes are likely Wednesday and Thursday nights away from urban areas and large bodies of water, and then it will warm up again next weekend into the middle of the following week while staying dry, though not nearly as warm as today and Monday. Uncertainty drastically increases afterward, but it is likely that the inevitable progression of autumn will lead to more frequent and perhaps bigger temperature swings as well as more frequent storminess, though whether there will be enough rain to dent the drought remains to be seen, and it still appears to be warmer than average overall.

 

Meteorological discussion: 

 

Record warmth today and Monday with dry and sunny conditions 

 

A classic, rather amplified upper-level trough in western North America (-PNA) and ridge in eastern North America will be dominating through Monday, with daily and possibly even monthly record highs in jeopardy today and Monday. Full sunshine, modest dry southwest flow, and drought conditions that allow all of the sun's energy (even with the much lower October sun angle) to go into heating up the ground and near-surface air. The downslope areas of far southwestern Quebec, eastern Ontario, and central Maine could approach 86F (30C)! Increasing southwesterly wind and clouds will lead to a warmer night Monday night, with parts of the St. Lawrence and Champlain Valleys not even getting below 60F (16C) as the wind stays up all night and gets channeled in the valleys.

 

Source: TropicalTidbits

 

 

Record warmth comes to abrupt end with rain later Tuesday, then much cooler with widespread frost and freeze Wednesday and Thursday nights

 

The summer weather will come to an abrupt end later Tuesday, although most of Tuesday will still be quite warm south of the U.S./Canada border ahead of a strong cold front that will bring widespread modest rain for several hours at any one location, the first rain in almost 2 weeks. The rain will be short-lived, and by Wednesday, another broad dry Canadian surface high-pressure system will be in our region again, but with much cooler air from the northwest. Wednesday and Thursday nights will likely feature the most widespread freeze and frost so far this fall across the region, including even the lower elevations except for urban areas and areas near large bodies of water.

 

Source: TropicalTidbits

 

Warms up and remains dry for weekend into middle of the following week

 

The cooldown will not last long, with the +NAO and +AO allowing for a rather fast-moving weather pattern. The surface high-pressure system will move southeastward into our region by Friday, allowing the cool air mass to become stable and a decent warmup to ensue but with no moisture, a very familiar cycle over the past 2 months with these high-pressure systems. Another upper-level trough will big into the western U.S. next weekend, allowing another persistent upper-level ridge to dominate across eastern North America, a change from model runs just a few days ago, and signaling a delay in any real change in the weather pattern. While it won't be as warm as today and Monday, this means that it will likely remain dry and mostly sunny again for a while through the middle of the following week.

 

Source: TropicalTidbits

 

 

Source: Climate Prediction Center

 

 

Uncertain afterward, but likely more typical autumn temperature swings and at least occasional storminess

  

Afterward, there is considerable model disagreement, as we would expect for so far out. With the PNA, NAO, and AO both rapidly trending towards near zero, allowing for the West trough/East ridge pattern to break down somewhat and also allow subarctic to arctic air to push farther south into the mid-latitudes, it appears unlikely that we will get such long stretches of warm, dry, and sunny weather again. Upper-level troughs and surface low-pressure systems will likely become more frequent, bringing at least occasional rain chances, though it is not clear if these systems will have rich Gulf of Mexico or western Atlantic moisture to dent the drought, or if they will have less moisture with unimpressive rainfall amounts like most recent systems. It also still looks to be warmer than the climatological average overall, but it does appear that there will finally be more frequent and perhaps larger temperature swings more typical of autumn, rather than the consistent warmth or very gradual temperature changes with the huge surface high-pressure systems that we have frequently seen in the past 2 months. However, it is also noteworthy that impressive cold outbreaks that models have shown in the long-range lately have turned out to be short-lived dry, cool spells with continuing and intensifying drought, with any big change to the weather pattern that the models show keep being delayed.

 

Source: TropicalTidbits