Early Heat Wave for Southeast

Current weather map across SE

For late May, today is nice with mostly sunny skies and temperatures in the upper 80s to lower 90s. But, the atmosphere is already dry (as shown by the green line, a profile of moisture in the atmosphere from the morning weather balloon at NWS Birmingham), leading to the large areas of clear to scattered clouds and no rain. About the only storms today are in middle TN and just east of Atlanta.

Weather balloon data from 7 am today at BHM. Red is temperature, green is dew point
High-resolution visible satellite (top), regional radar composite (bottom)

However, changes are coming, as a ridge of high pressure moves almost directly over the SE, cutting off any cooler, more humid air off the Gulf of Mexico. Plus, temperatures in the Gulf are still cool, in the 70s across most of the northern Gulf, and only in the lower 80s at shallow beach locations like Orange Beach, AL and Panama City Beach, FL. So, humid air will have a hard time making it in here over the next week, and our atmosphere will stay dry.

Gulf of Mexico water temperatures

This causes heat because 1) we don’t have many clouds and the sun this time of year is near maximum strength due to its high angle above the horizon, 2) the afternoon thunderstorms we normally get this time of year that cool us off won’t occur in the dry atmosphere, and 3) without afternoon storms to rain on the ground, the ground will slowly dry out, allowing more of the sun’s energy to go into heating the air than drying up soil moisture.

Surface pressure and winds on Monday (pivotalweather.com)

We still have a decent south wind today and tomorrow, bringing some of that slightly cooler air off the Gulf in here, so we should mainly have high temperatures here in Birmingham between 90 and 92. But the winds calm and turn SW by Friday and the weekend.

Computer models have a hard time with the layer of air we live in near the surface, and statistics derived from models have difficulty with abnormal events. So I take a simpler approach that has worked for years. Based on that, my best shot at high temperatures in BHM for the next several days is:

Today: 91 Thursday: 92 Friday: 94 Saturday: 95 Sunday: 97 Monday: 98

The good news is that humidity levels will remain low, with dewpoints in the 60s. So, heat index values will not be much higher, if any, than the temperature. But, in a slightly drier heat like this, people can get dehydrated because they don’t realize how much they are sweating. So, stay hydrated. Since this is coming on so quickly (last Summer it never got above 97 and that occurred in September, with most of May through August being unusually mild), check on the elderly and anyone who may not have air conditioning. Close south-facing window shades and blinds. And one final note, UAH research has shown that it can often be 4-5 degrees hotter right near the ground than the official temperature (taken at 2 meters). So, where dogs and cats are, it could easily be over 100. Bring them in during the day if you can, and make sure they have plenty of water. If you are going away for the Memorial Day weekend, make sure they have a cool place to go (basement, etc.) and enough water.

Dr. Tim Coleman

Consulting Meteorologist, Coleman and Knupp LLC

Twitter @timbhm

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