Tuesday, July 12, 2011

7/12 - 10am - Another Day of Incredible Heat

Here we go again. It's already 87° with a dew point of 81° in Louisville and we're just getting started. See that condensation on my door to the left? That started at 10pm last night when the temperature dropped a couple degrees and just now cleared up with sunlight and a bit of heating. That's some crazy humidity right there. I think we'll get near yesterday's high of 97 again today, but like yesterday the dew point is the bigger story. With such a high temperature and high dew point in the low 80's (which is almost unheard of in Louisville), heat index values will be exceeding 110° again. An Excessive Heat Warning has been issued that goes from 11am this morning to 8pm this evening.

...But wait! There's more. We're under a Slight Risk from the Storm Prediction Center for severe weather this afternoon as a cold front approaches the area from the north. This is mainly a wind threat (notice the 30% wind risk red area on the right), but there's also a small chance for hail. A lack of wind shear and helicity (turning of the atmosphere) will eliminate any tornado threat for the most part. This front should be the trigger for some southward-moving clusters of scattered storms this afternoon. With all the heat energy and moisture in the area, there's no question that some of these could reach severe limits as the SPC indicates. Not everyone will see storms this afternoon, but those who do will receive quite a bit of rainfall, lightning, damaging wind, and a break from the heat. The cold front is positioned just south of Indianapolis right now and is moving fairly slow, so there will be quite a bit of time for storms to fire today and tonight before the front passes through sometime early tomorrow.

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