Why such hot temperatures now?

The obvious answer, of course, is that it is August in Alabama!  But, there are things going on in the atmosphere that produce the heat.  The main one is a lack of moisture to produce afternoon storms, that cool the lower atmosphere and keep the soil wet so some of the sun’s radiation goes into evaporating water instead of heating the ground.  But, the atmosphere is fairly dry once you get just above the ground.  Here is this morning’s balloon data from NWS Calera:

The red line is temperature, and the green line is dewpoint.  Notice how quickly the dewpoint drops with height.  A few isolated storms may develop, but there is little moisture above about 800 mb (6,000 ft.), so storms that do try to form will have this dry air mixed in as they grow, either stopping them from producing rain, or making them produce less.

Without any storms to cool the air nor wet the ground, we still have more radiation coming in from the sun than we have going out in August in Alabama.  The air is barely moving (no cooler air coming in from anywhere else), so the net is that it warms up a little each day.  We’re one degree ahead of yesterday (when the high was 96), so expect 97 or 98 in BHM today.  Tomorrow, we’ll be close to 99 or even 100 in some spots.

Category: Met 101/Weather History