The cold front that came through Friday has moved back north as a warm front...and temperatures have climbed into the mid and upper 80s over central Alabama with dewpoints in the 60s. This, combined with cool air aloft, is producing very large instability (CAPE near 4000 J/kg) over NW AL. The air is a little less humid as you move farther east (CAPE in BHM 2,500 J/kg), but that is still plenty to keep the storms over NW Alabama now going at least to TCL and BHM. The old front is diffuse, but it's enough to provide a focus for the storms.
The balloon data from Calera indicate some dry air up around 4,000 feet. This allows falling raindrops to evaporate, produce cold air (like you feel cold when you get out of a pool even though it's 80 degrees outside), and this dense cold air sinks rapidly to the ground producing microbursts of strong wind. Radar already shows winds up to 65 mph in these storms around 1,000 ft. off the ground, so wind gusts of 40-65 mph are the main threat as the storms move across the area.
Large hail is also possible.
Dr. Tim Coleman
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