BIRMINGHAM, Ala. (WBRC) - If you watched our forecast last night, the most snowfall that was mentioned was a few snow flurries as our winter storm system exited the state. To many meteorologists surprise, including this one, much of the area had over an 1″ of snowfall on the ground. Streets, cars, lawns, and rooftops were covered. This further aggravated the road problems we were already dealing with.
How does a surprise snowfall happen? Not one computer model last night predicted snowfall and there was nothing on radar approaching from the west. Low clouds and cold temperatures were in the forecast, but nothing more than brief flurry expected. The bursts of snowfall began happening around sunrise with the slight increase in surface temperatures.
This is called convective snow and it is a problem. Typically, we refer to convection when dealing with stormy weather. Convection can also happen during Winter weather.
As the surface temperature increased during the morning hours, there was a significant difference in the temperatures between the low clouds at around 2,000 ft. and the surface. This allowed for the air to begin to rise. Just like rising air helps create a thunderstorm, rising air can create the bands of snowfall we saw this morning.
With this type of forecast, we are dealing in the microscale with cloud physics. These fine details are often too small for even our best forecast models to detect.
WBRC Chief Meteorologist