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The National Weather Service in Upton ...

Heat Fueling Some Severe Weather

5/31/2011, 7:02:55 AM

Tuesday, 11:35 A.M.

Record heat blistered large sections of the country on Memorial Day. With 90s showing up in a lot of places, and pretty high dew points as well, you had to figure there would be some thunderstorms around, and that some of them would likely be severe. All you needed was some sort of spark or trigger, and that was provided by a powerful storm coming out of the eastern Rockies and heading for the Upper Midwest. And here is how the severe weather scorecard played out yesterday and last night:

While it will be an active afternoon and evening downstream ahead of a cold front, I suspect the numbers won't match up, as the storm in question is lifting northeastward across Quebec at this hour, and the thunderstorm so far today have not been nearly as potent. Still, the risk encompasses areas from the Great Lakes southwestward across the middle Mississippi Valley, perhaps even to portions of the southern Plains:

Out ahead of the front where there is ample sunshine, it will be another scorcher with temperatures of 90 or better, along with high humidity. This heat and humidity combination will stretch into the mid-Atlantic states, though New England will see less of the heat thanks to a weak cold front that sailed across the region last night. Then tomorrow, as the front presses farther downstream, there will be one last opportunity for severe thunderstorms:

Temperatures in the East ahead of this front will be well into the 80s, if not 90 or better, and that's after an uncomfortably warm and humid night tonight. Once again, that heat and humidity will be the fuel, and the cold front will be the spark to ignite some of the strong thunderstorm activity as the day wears on.

After the front passes, a breath of fresh air, which essentially means much lower humidity. The cooling will be modest at best, with the strongest cooling restricted to the Upper Midwest and the northern Lakes over to northern New England. Areas from the Ohio Valley to the interior mid-Atlantic will still be warmer than normal, just not double digits above average!

Right on the heels of this cooldown will come another surge of heat out of the eastern Rockies and across the Plains on Thursday. Initially, the thunderstorms will come AHEAD of the heat, associated with a warm front moving through the Dakotas into the Midwest. These thunderstorms are most likely to move across the northern and eastern Lakes sometime Friday, and may have some staying power farther to the east and southeast into New York, western New England, and perhaps spotty areas of the mid-Atlantic Friday night into Saturday as the heat tries to come right back in from the west.

The farther north you go, the more resistance there will be to this next heat surge, so that much of New England misses out on it, especially northern and eastern areas. There will, of course, be still another cold front coming in to put the squeeze on this heat, but in the face of a fairly strong upper-level ridge in the Plains and Mississippi Valley, there may not be as much severe weather to contend with this weekend.

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

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