Tuesday, 11:55 a.m.
Summer is still nearly four weeks away from officially getting underway, but for all practical purposes, it has started with the passing of the Memorial Day weekend. There are clearly more signs that the summer season is upon us, yet we're but a week removed from frost in parts of Pennsylvania and New York. And today, a backdoor cold front pressing southwestward across New England is reintroducing chilly air to the region, with temperatures now down in the 50s in Boston with a strong east-northeast wind blowing in off the chilly waters of the Atlantic.
If you step back to try to get a feel for how the weather has been behaving, one of the things that comes out of the pattern so far this spring is just the general lack of heat in much of the country. Take away the heat that blistered the West earlier this month, and most places east of the Rockies have only had a token amount of heat at best. Granted, it's still May, but even this week, there's just not going to be a lot of heat. That will begin to change some going into the weekend, especially on the Plains.
That will happen once this pesky upper-level low gets out of the way. Yes, it's the same one that at the beginning of last week was rolling down through the Northwest and heading into California. The same upper-level low, as it rolled into the Southwest at midweek, helped ignite severe thunderstorms over the eastern Rockies, complete with large hail, damaging winds, flooding downpours and tornadoes. Yes, the same upper-level low that finally rolled out of the Rockies over the weekend, drenching parts of Texas with excessive rain on Memorial Day.
This same upper-level low is now inching across Texas. Here's the 12z May 27 NAM 500mb forecast for this evening:
This puts East Texas and Louisiana into southern Arkansas and Mississippi at the greatest risk for flooding downpours. Examine the 36-hour total precipitation forecast through tomorrow evening:
If you look at the same 500mb forecast for Friday afternoon, this upper-level low more or less grinds to halt and continues to unravel slowly:
Part of the reason why this upper-level low won't get much farther east is that there will be such a sharp downstream upper-level trough over the Northeast. For the next couple of days, the cooling will be accomplished by turning the wind in off the Atlantic, bringing a marine-cooled environment across New England this afternoon and tonight, and through the mid-Atlantic tomorrow and tomorrow night into Thursday. Then, with this upper-level trough swinging through late in the week, there will be a different kind of cooling taking place. With a much drier air mass moving in over the weekend, the nighttime lows will drop significantly, and the daytime highs will likely remain at or below average. The sum total of that is a coolish weekend from parts of New England down the Eastern Seaboard. Look at the projected temperature anomalies for Sunday:
Remove this cool air and the lingering remnant of an upper-level low between the lower Mississippi Valley and East Texas, and you would actually have an upper-level ridge over much of the country:
With that in place, it look and feel a lot more like summer this weekend across the Rockies out into the northern and central Plains, eventually stretching into the Midwest by Sunday.
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