Plain-language summary:
A slow-moving weather pattern will dominate for at least another week. Today will be the last sunny day in a string of sunny days across the region in areas west of Maine, New Hampshire, and eastern Quebec. A little rain will fall tonight into Monday and should tamper the fire threat that has been ongoing mostly southeast of the Appalachians. It will dry out again with slightly mild temperatures for Tuesday and Wednesday, but then a slow-moving storm will bring several days of rain and showers over our region starting on Thursday, with snow possible at the highest elevations initially but then possibly spreading to lower elevations intermittently by next weekend, though any accumulation will likely be confined to higher elevations. It will likely warm up for a few days afterward, though cold air could return for the end of November and beginning of December, with how cold being quite uncertain for now.
Meteorological discussion:
It will be yet another mostly sunny day for most of the region, perhaps the 5th in a row except for Maine, New Hampshire, and eastern Quebec that was marginally affected by the cut-off low over Atlantic Canada on Friday and Saturday. It is a slow-moving weather pattern due to the prominent Greenland and high-latitude blocking (-NAO) and slow-moving low-pressure systems tunneling underneath the blocking ridge. There is also an upper-level trough in western North America promoting an upper-level ridge in eastern North America, though the blocking is preventing any surge of warm air into our region, with surface high pressure, clear skies, light winds, and mild temperatures instead over our region. A weak disturbance moving southeastward will bring increased clouds and some showers for many tonight into Monday, though amounts will be light, like they have been for weeks now. However, it might moisten the ground enough to curb the unseasonable and unusual fire threat that has been going on especially southeast of the Appalachians, where the drought is more severe and the recent northwesterly winds are stronger and downsloping, drying out the air even more.
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| Source: Climate Prediction Center |
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| Source: TropicalTidbits |
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| Source: U.S. Drought Monitor and NOAA |
A low-pressure system will strengthen over the southern Plains tonight into tomorrow and move northward into Minnesota by Monday night, and then stall out and occlude over southern Manitoba by Tuesday night, being blocked by the blocking ridge to the northeast. At this time, another disturbance will move into the southern Plains and spawn a secondary surface cyclone over the Appalachians by Wednesday, strengthening and eventually becoming the primary cyclone as it heads almost due north into the Great Lakes on Thursday. Because of the blocking ridge, the systems will be slow to move, with upper-level ridging and surface high pressure persisting and causing more dry weather for our region late Monday through Wednesday with variably strong northerly flow and mostly steady, slightly above average temperatures.
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| Source: TropicalTidbits |
The Great Lakes cyclone will finally push far enough northeast on Thursday to affect our region, with widespread rain Thursday and Friday. It might be cold enough at the highest elevations for snow, but with the storm that far west, the cold air will be sent southward into the central Appalachians and then weaken as it heads eastward to the south of the cyclone track and cuts off from the main jet stream, while warm and moist Atlantic air will advect northwestward north of the cyclone track, creating an upside down temperature structure that is really only possible with a blocking pattern like we are seeing now. The storm will also be weakening but also move only slowly to the east, with disturbances rotating around the cut-off low likely producing intermittent showers through next weekend, though the exact timing and location is uncertain as is always the case with slow-moving cut-off lows. A disturbance over eastern Canada could bring in a reinforcing shot of cold air on the back side of the storm next weekend, perhaps enough for everyone to change over to snow at some point. However, there is still no real connection to Arctic air, and the strong circulation of the upper-level low could just throw mild Atlantic air into whatever cold air is trying to move in. Thus, temperatures look very marginal at lower elevations, and with the spotty and light nature of precipitation, any snow accumulation looks to be confined to higher elevations, unless a well-timed and well-positioned disturbance rotating around the cut-off low strengthens enough for heavier precipitation and dynamic cooling on the northwest side. So for most lower-elevation areas, the wait for the first snowfall continues.
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| Source: TropicalTidbits |
After next weekend, the blocking pattern (-NAO) weakens but will still be present in a weakened form. However, it is increasingly likely that another upper-level trough moving into western North America around then will promote upper-level ridge building to the east and kick out the cold air for at least a few days. But if an upper-level ridge can poke into northwestern Canada (EPO turning negative), that would force Arctic air to push southward into central and eastern Canada and then northern New England for the very end of November or the beginning of December, which would be the first widespread intense cold air outbreak over North America in this otherwise unusually mild fall. However, there is considerable model disagreement on this, with some model runs showing a flatter, more zonal jet stream or even an upper-level trough over western Canada, which would promote mild westerly flow across North America and lock the arctic air too far north to influence our region, meaning that even the cooldowns with northerly flow will not be very cold, perhaps barely cold enough to snow. If the milder, perhaps less likely solution pans out, most of the region could see one of the latest first snowfalls on record.
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| Source: TropicalTidbits |
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