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    Volatility Eases, but Weather Pattern Remains Dynamic

    5/22/2013, 6:52:44 AM

    Wednesday, 11:30 a.m.

    Over the past 24 hours, the reported number of tornadoes was thankfully zero, a noted improvement after the deadly and destructive tornadoes of Monday afternoon into Monday night. That said, there were still plenty of incidents of severe weather Tuesday and Tuesday night, many of which were attributed to strong and gusty winds in thunderstorms that stretched from the southern Plains all the way to New England:

    As the upper-level low over now over the Midwest continues its slow, unraveling and eastward migration, the area of severe weather is advancing eastward along with it. The cooling aloft combined with the very warm, moist air in the low levels of the atmosphere will aid in the development of strong to severe thunderstorms this afternoon into tonight from the Tennessee Valley northeastward:

    There is a slight risk of additional severe thunderstorms tomorrow east of the Appalachians ahead of the oncoming cold front, but sufficient cloud cover may limit the instability, thereby reducing the areal extent of any severe weather. The bigger risk tomorrow may be that of flooding downpours in parts of the mid-Atlantic up into New England.

    That risk may be elevated later tomorrow night into Friday across mainly New England as the front slows down. There's a fair amount of moisture lying in wait over the Bahamas right now:

    The models have all been trending in the direction of redeveloping the upper-level low to one degree or another. It will serve two purposes - one will be to entrain that tropical moisture into the upper-level storm going into Friday to enhance the rainfall across parts of New England for a time. The other will be to enhance the cooling in the wake of the trough, with the cool air drilling southeastward from the Midwest all the way to the Southeast.

    And therein lies another fascinating dynamic of the weather pattern - temperatures going from 15 above normal yesterday and today in some places to that much below it Friday and Saturday! Look at the projected anomalies Friday:

    One more time for frost in parts of the Northeast Friday night or, more likely, Saturday night? It is still possible, even into parts of Ohio and Pennsylvania nestled under the surface high. And dry air driven right down to the eastern Gulf Coast and throughout the Southeast yet again. Great for sleeping and comfort levels over the holiday weekend, but the complete lack of moisture could become problematic over time.

    Not to be outdone, the Northwest is seeing their own upper-level low roll in from off the Pacific, and it's even more intense that the one that moved out onto the Plains Sunday into Monday of this week. Here's the 12z 22 May NAM 500mb forecast for this evening:

    The air mass associated with it is cold enough to support snow in the Cascades. It, too, will mean a much below-normal chill the next two or three days throughout the West before there is some slow recovery over the Memorial Day weekend. But it's not like we'll flip a switch, an upper-level ridge will move into position over the West, and it will dramatically warm. No, that won't be the case. There will be other features over the next week, so as the first upper-level low rolls out later this weekend, it will be replaced by another next week to extend or renew the cooler-than-normal pattern there.

    And if that's going to transpire there, then by rights there should be a downstream ridge that develops somewhere. Right now it would appear that it will develop over the Rockies and quickly spread onto the Plains. Where there's little resistance to it warming, temperatures will have no trouble jumping back above average this weekend. That appears to be the eastern Rockies and western Plains. Farther north and east, the spread of warmer air will be slower and harder, leading to more clouds and some showers and thunderstorms. These are likely to expand east and southeast over time during the rest of the holiday weekend, reaching the Ohio and Tennessee valleys Monday, and perhaps points farther east later in the week.

    I haven't even talked about the tropics today, either! There are some hints of trouble brewing early in the first week of June over the western Caribbean. I'll address that issue tomorrow!

    The views expressed are those of the author and not necessarily those of AccuWeather, Inc. or AccuWeather.com


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