Monday 9:30 AM
With a high pressure area over the Northeast and a strong storm well east of the Carolinas, it should remain rain-free most or all of this week from Maryland to Maine and out into the Great Lakes region. Two concerns: (1) light flow off the ocean has produced patches of clouds from New Jersey and Delaware west to the the Appalachians. These cloud decks are notoriously difficult to predict, but they should not cause precipitation; (2) with light winds, clear nights can allow temperatures to drop to the saturation point, and this can mean late night and morning fog. Since the sun is much lower in the sky than during other times of the year, there is less energy available to warm up and dry out the low-level chilly air each day.
A strong cold front will cross the Great Lakes Friday and then speed off the East Coast. Sharply chillier air will move in behind the front and there could be an outbreak (rather brief... 12-24 hours) of lake-effect snow from the eastern Great Lakes into the mountains. While the cold shot will not be permanent, it appears the regime will change to one that features a succession of cold fronts, with some wintry air behind each front. Any low pressure areas that form while cold air is in place will capable of causing snow. One example of this is depicted on the GFS model (1 AM EST run from Monday) for next Tuesday. The map is here, but I want to stress that this development is far from certain, and that this and other models have offered varying solutions for this time period (as is typical more than a week in advance).
Yesterday, there was a sharp boundary between air that was cool and dry enough to suppress thunderstorms and air that was warm and humid enough to support them. This map shows the lightning strikes from 8 a.m. ET yesterday to (almost) the same time today.
As the second low pressure area develops off the East coast, it will work in concert with a high pressure area from Canada to orchestrate cooler-than-usual conditions with showers in the Middle and North Atlantic states Thursday.
Looking ahead to <strong>next</strong> weekend, the Mothers Day Weekend, we see quite a difference between the GFS model and European models on where cold Canadian air is heading at 2 a.m. Sunday.
Rain is spreading across the Middle Atlantic states today. Dampness will linger from southern New York state to Virginia tomorrow even as the main rain area moves offshore.
For the rest of the week and this weekend, the upper-air "steering winds" will be arranged in two separate streams. The northern branch will send air from central Canada toward New England.
In the Northeast today, the low pressure area shown on this map will move to the East Coast today, pulling the front south as a cold front. Showers and gusty thunderstorm will affect areas south of the front while steady rain and gray skies are common to the north...