Thunderstorms today and tonight then cooler

Published 7:00 am Tuesday, February 2, 2016

Showers and thunderstorms will break out this afternoon or tonight in the warm, humid air ahead of an approaching cold front. Make sure you’re able to receive severe weather warnings via a cellphone app, weather radio, or local radio or television.
For the past few days we have been on the western side of a large high-pressure system centered over the mid-Atlantic Ocean.
Because winds circulate clockwise around high pressure in the Northern Hemisphere, winds on the western side of a high are generally from the south.
Those southerly winds over the last three days have brought in warm, moist air from the Gulf of Mexico giving us high temperatures in the 70s. Dew point temperatures, an indirect measure of the air’s water vapor content, have been in the 60s. That’s much more humid than the 20s and 30s we typically experience during cold, dry spells this time of year.
Cold air currently over the Great Plains is headed our way. The leading edge is moving out of Texas into Louisiana today and will be reaching us tonight.
The wedge of colder air, an associated low pressure trough in the upper atmosphere, and a strong surface low moving northeast from the southern Great Plains toward the Great Lakes will all help lift the warm, moist air ahead of the front.
As that air is lifted it will cool, and the water vapor will condense into clouds resulting in showers and thunderstorms. Because, the rising motion within this complex of systems will be especially vigorous, some of the thunderstorms may become severe.
Late tonight, after the front moves off to our east and the surface low moves farther away to our northeast, the rising motion in the atmosphere will be replaced by sinking motion as a cold, dry dome of surface high pressure extends from the Rocky Mountains into the Gulf South.
On Wednesday and Thursday we will be on the eastern side of the high-pressure system, the opposite position relative to the high’s center compared to our position the past few days relative to the mid-Atlantic high.
On Wednesday and Thursday, the clockwise circulation of the high centered to our west will result in winds from the north.
It will be breezy on those days because we will be in a zone where the surface air pressure change is large over a relatively short distance. This shows up on weather maps as an area where the isobars (lines of equal pressure) are close together indicating a large pressure gradient.
Dew point temperatures, in the 60s today and tonight, will fall steadily once the cold front passes and drier air flows in.
By Thursday dew points will be in the 30s and by Friday the 20s indicative of the much drier air.
Lows on Friday and Saturday mornings are forecast to dip into the middle to lower 30s, cold enough to produce a couple of frosty mornings if the winds die down.
Relatively cool conditions will persist into the weekend, and, while it will likely remain dry, there’s a chance that an upper level disturbance will be strong enough to kick up some showers.

By Skip Rigney

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