Sunday, August 7, 2011

Chance of evening storms "under the ridge," then a pattern shift means cooler weather

Massive high pressure has maintained a grip on Mid-South weather for several days, bringing nearly daily chances of eclipsing the 100 degree mark. A respite on Friday was caused by thunderstorms that managed to move under the ridge thanks to a disturbance in the mid levels of the atmosphere.

After nearly reaching 100 again today, another one of these disturbances is moving slowly across AR and causing scattered storms over the central part of the state. This impulse should move just south of the metro area this evening, but will bring a chance of t'storms, mainly over northwest MS and east-central AR, between 6-11pm.

As we head into the new work week and the first week of school for many area children, the strong ridge of high pressure will begin to retrograde to the west, putting the Mid-South in a northwest flow.  This means that the upper level wind will be flowing from northwest to southeast over the area.  In the summertime, this pattern lends itself to the possibility of repeated rounds of thunderstorms, particularly at night or in the morning hours.  These rounds of thunderstorms are hard to time more than a day or two in advance, so for now the MWN Forecast includes a daily chance of thunderstorms this week as the pattern could stick around for a while.

The bad part of this pattern is that, depending on the timing of the storms, they could bring chances of damaging wind and hail. The good news, other than the rain chances, is that it will also mean reduced high temperatures. So, the end of the upper 90s to lower 100s is within sight.  An Excessive Heat Warning remains in effect through Monday evening with heat indices near 110 again Monday.  Excessive Heat Warnings are not anticipated for the remainder of the week after Monday.

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2 comments:

Anonymous said...

Hello.
You mentioned the severity depended on the time of day...if these storms occur in the overnight hours, does the severity lessen? You also said these storms usually do move through during the nighttime hours, so...maybe these guys don't need the sun's energy to be severe? Trying to decide if I need to sleep with my weather radio. Thank you.

MWN/Erik said...

I probably should have been a little clearer... I indicated that th severity depended on the timing of the storms. It really depends more on the timing within the life cycle of the storm complex than the time of day, though they are typically weakest around sunrise. And yes they can maintain severity well into the night. Always a good idea to keep the weather radio on alarm mode so that you are never caught off-guard. Thanks for your comment!

-Erik