Plain-language summary:
It will be chilly and rainy for most of the region today, with it turning warmer and sunnier for Monday and Tuesday. It will turn cool and rainy again on Wednesday, then a bit drier especially in northern areas but still a bit cool on Thursday, and then perhaps turning more rainy or showery again starting on Friday, though which days will rain are uncertain beyond Friday. Cool and at times unsettled weather then prevails through at least mid-May, with no summerlike heat and humidity expected.
Meteorological discussion:
After a seasonably mild Friday and Saturday away from the coast, it will be rather chilly today almost everywhere despite southerly winds ahead of a subtle cold front draping down from a low pressure system way up in northern Quebec, due to a thick overcast and rain spreading from south to north today. The southerly winds will transport some of the cool maritime air from the western Atlantic to our region, blocking the really warm air to the southwest again. By Monday, the weakening cold front will have passed through, with slightly cooler air aloft, but surface temperatures will actually be much warmer, slightly above average, with more sunshine and drying offshore westerly flow. Tuesday's temperatures will be similar to Monday's. Both Monday and Tuesday will feature highs in the 60s F (mid to upper teens C) to the north and 70s (lower to mid 20s C) to the south over lower elevations, though nighttime lows will be much cooler due to the drier air.
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| Source: TropicalTidbits |
As this happens, a potent and unseasonably cold storm will slowly move northeastward from the Rockies. The overall trough will move very little, but shortwave disturbances will eject from it and move eastward to our region later in the week. The first disturbance will move into our region on Wednesday, with the surface low pressure just to the south, ensuring that our region will be on the cold side of the storm. With a steady light to moderate rain for most areas, especially in areas south of the U.S./Canada border, daytime temperatures will be unseasonably chilly, likely below 60F (16C). It will likely be drier on Thursday, especially in northern areas, but with a slightly cooler (though not very cold) air mass with a very broad surface high pressure to the north over Hudson Bay into central Quebec bringing light northerly flow into our region. Depending on how the different pieces of energy are dispersed in the upper-level flow, southern areas could still be wet. Another disturbance with the surface low pressure going to the south will likely bring more rain and chilly temperatures on Friday. This chilly and unsettled pattern is brought on by high-latitude blocking (over Nunavut instead of Greenland, hence the still positive NAO and AO) preventing the heat and humidity building in the southern U.S. from pushing north into our region, despite the repeated troughs in western North America (-PNA) that would normally allow such warm surges.
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