Plain-language summary:
It is unseasonably warm and breezy today, with the warmest in eastern Ontario and northwestern New York, with high fire danger. Widespread drenching rain will occur tomorrow, with even a broken squall line featuring a brief period of heavy rain and strong winds for many before it abruptly turns cooler. No major rainfall is then expected for the rest of the week, but cooler temperatures, increased clouds, lower sun angle, and higher relative humidity will prevent the ground from drying out as quickly as after previous rain events this autumn and should prevent the drought from intensifying further. It will be mostly dry on Tuesday with some breaks of sunshine and seasonably warm temperatures before widespread showers occur Wednesday and some showers still possible on Thursday with cooler but not particularly cold temperatures. Lake-effect rain is possible on Thursday in northwestern New York. It gradually clears out later Friday into next weekend with widespread frost and freezes likely. It then likely warms up modestly and stays dry for a few days before turning cooler, cloudier, and more unsettled again, though it is unclear if any major rainfall will occur. There is also still no sign of true arctic air entering our region, leading to modest cooldowns and muted temperature swings again.
Meteorological discussion:
Unseasonably warm and breezy with high fire danger today, then rain, briefly heavy Monday before turning abruptly cooler
Today is briefly unseasonably warm across the region as the weather pattern has finally become more amplified temporarily, with a short-wavelength but deep trough in the Great Lakes associated with a rather strong though elongated surface cyclone in northern Ontario and upper-level ridging over Atlantic Canada. Today, our region is east of the storm, with decent sunshine filtered through high clouds and strong southerly flow bringing breezy conditions and much warmer air. It is the warmest in eastern Ontario and downsloped regions of northwestern New York and extreme southwestern Quebec, where isolated temperatures of 80F (27C) are occurring! To the east, the southerly flow is modified by the previous cooler air mass and the northwestern Atlantic Ocean. Given the warm weather, strong winds, drought, and lack of rain for several days, the fire danger is unusually high today, with a rare red flag warning issued for northern Vermont and northwestern New York. On Monday, the storm will have moved into our region, with widespread rain and even a weak broken squall line with brief heavy rain and strong winds along the cold front, especially south of the U.S./Canada border, with abruptly cooler air behind it. A few spots could even have thunder, though the clouds will prevent daytime heating and instability, and it is so late in the year that there is virtually no chance of anything severe.
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| Source: PivotalWeather, TropicalTidbits, National Weather Service |
Seasonably warm temperatures with breaks of sun Tuesday, then widespread rain and showers on Wednesday, then leftover showers and modest cooldown for Thursday
The warmth will not last and will be gone by later Monday, with a -NAO and increasing PNA favoring upper-level ridging in western North America and deep upper-level troughing in eastern North America. The -NAO and associated high-latitude blocking will also slow the weather pattern down and make it easier for storm systems to cut-off and move very slowly, bringing showers to an area for several days. After Monday's storm, Tuesday should be dry for most, perhaps with some sunshine and seasonably warm temperatures as the true cool air mass remains to the west, and the southwesterly flow modifies any cooler air that initially gets pushed into the Great Lakes. Another system, this one being cut off, will slowly move into the region on Wednesday, bringing a period of widespread showers but without the strong dynamics that Monday's storm will have, with the showery nature of the rain aided by the cooling aloft. As the cut-off low slowly moves across Quebec, any steady rain will end by Thursday, but scattered showers and widespread cloudiness are likely given the low-level moisture and relative low pressure that will be in place, something that is very common in late fall. The west to southwesterly low-level flow and the Great Lakes still warm from summer will even favor lake-effect rain to affect northwestern New York. Temperatures will be seasonably cool, but the west to southwesterly flow will lead to any cold air taking an indirect path and being modified over the Great Lakes before reaching our region. Wind and clouds will likely prevent a frost or freeze for most locations. Also, even with the upper-level troughing, there is still no real arctic air involved, perhaps due to the neutral to increasing positive AO. Despite the lack of major rainfall after Monday, the clouds, lower sun angle, and higher relative humidity will lead to slower evaporation and slower drying of the ground than after previous rain events this autumn, preventing the drought from intensifying further.
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| Source: TropicalTidbits |
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| Source: Climate Prediction Center |
Gradually clearing out Friday into next weekend with widespread frost and freeze likely
By Friday, the cut-off low will have moved farther east, and surface Canadian high-pressure will slowly push into our region into next weekend, which should gradually clear the skies out and lessen the wind. If the surface high-pressure traverses directly over our region as models currently indicate, widespread frost and freezes are likely, the most widespread of the fall so far, perhaps except for the immediate shoreline of large bodies of water like Lake Champlain or the Atlantic Ocean and in downtowns of urban areas. The high-pressure system will likely squash another storm slowly traveling across the U.S. to our south during this time, though this is not a guarantee yet.
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| Source: TropicalTidbits |
Dry and modest warmup early following week, then cooler, cloudier, and more unsettled again but not particularly cold later in the week
For early the following week, the PNA eases back to near neutral as an upper-level trough moves into the western U.S., which will promote upper-level ridging in eastern Canada and dry and maybe warming weather, at least during daytime, in our region. The surface high-pressure location over eastern Canada does not favor the southerly or southwesterly flow needed for a truly major warmup. There might actually be low-level cold air sneaking in from the northeast instead, with continued nighttime frosts and freezes if the sky is clear enough. Whatever warmup will not last long, as the PNA will likely return back to positive later in the week while the NAO remains negative. This will encourage upper-level troughing to return to eastern North America, including our region, with a return to cooler, cloudier, more unsettled conditions, though it is unclear if there will be any actual major rainfall. Any system that affects our region will be slow-moving with the high-latitude blocking, and there is even a small possibility that future Hurricane Melissa that develops this upcoming week in the Caribbean has at least a small impact on our weather the following week if it is timed right to be picked up by an amplifying upper-level trough over the central and eastern U.S., though it is way too far out to tell. There also still appears to be a lack of true arctic air, rendering any cooldown relatively modest and limiting the temperature swings that have been less pronounced than usual for most of this autumn. Even the arctic itself appears to remain much warmer than average for the foreseeable future.
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| Source: TropicalTidbits |
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