This past weekend was blustery, chilly and CLOUDY. One of the most difficult things in weather forecasting to predict is when low clouds called stratus clouds will break up, revealing sunshine. This not only wrecks havoc on your forecast for sunshine, but your temperature forecasts as well. This is more often the case in the winter when sunshine is weak due to a low sun-angle. The low sun angle disallows strong heating, which mixes up the atmosphere and breaks up the low clouds. This gave me nightmares when I lived in Cincinnati because cold air from Canada would sweep in after a strong cold front leading to cold air stratocumulus clouds, which wouldn't break up for DAYS on end. We don't get quite as much of an influence from the Hudson Bay Vortex, which is a strong upper level low pressure system that forms over the Great Lakes and keeps those areas cloudy and cold for weeks.
This past weekend, a strong inversion, or warm layer of air at about 3000 feet kept moisture trapped in the low levels of the atmosphere. This "lid" was difficult to break or mix out during the day due to thick clouds in place and strong north winds sending in more cold air. The image to the right is a weather balloon sounding showing the temperature and dewpoint profile in the atmosphere. The red line is the temperature and the green line is the dewpoint. The key feature to note is how the red line jumps sharply to the right from the bottom upward. This is the strong warming at 3000 feet I was referring to earlier, or the strong temperature inversion. Notice how the red and green line also are fairly close together below this inversion. This indicates a high level of moisture in the low levels or lots of clouds. The inversion did not break until Sunday afternoon, when we finally saw some sunshine. The clouds overnight Saturday kept the temperatures from dropping as low as forecast.
In the spring and summer we can get Gulf Stratus which develops from southerly winds bringing in high moisture content inland from the Gulf of Mexico. This is especially the case in the spring when then shelf water temps off the Alabama, Mississippi and Florida coasts are cool and warm air moving over the colder water leads to advection fog and stratus.
Local 15 Chief Meteorologist Derek Beasley
