Time to talk summer weather forecasting in Alabama. Perhaps you are a newcomer to our state, or maybe you have lived here all your life. Either way, this will help you understand how forecasts work through June, July, and August.
Let me say up front that “probabilities of precipitation†are pretty much worthless this time of the year. On just about every afternoon, we will deal with a few showers and thunderstorms due to the combination of moist, maritime tropical air over the state, and the daytime heating process that makes air parcels rise. The showers and storms are usually very scattered, and tend to pop up in random locations. There is no way we can tell you at 7:00 in the morning where it will be raining at 3:00 in the afternoon. And, on most days, if you read a forecast from the National Weather Service, you will see that the “probability of precipitation†is either 20 or 30 percent. Of course, to any one person at any one place, for a forecast to be perfectly correct to them it is either raining, or not raining, so the chance of rain should be zero, or 100 percent.
With the typical airmass showers on a summer day, a handful of folks will get a good downpour for 15 to 30 minutes, but most people won’t see a drop. The dreaded “probability of precipitation†only gets you in trouble, and very few people understand how to use the product, including both forecasters and the public. We stay away from it like the plague.
Instead, we use descriptive words in our daily forecast that hopefully will be a little more helpful. But, the bottom line is that we simply don’t have the knowledge to forecast afternoon showers on a summer day properly. Generally speaking, most of the showers and storms come from about 1:00 until 10:00 p.m.
Having said all of this, we do have some skill in identifying small scale weather features (the daily sea breeze front moving northward from the Gulf, subtle short waves aloft, easterly waves, the strength of the cap, etc) that can either enhance or reduce the coverage of afternoon showers and storms. We also strongly suggest that you read our daily blog discussions and watch the Weather Xtreme video if you really need to know the likelihood of your neighborhood getting wet on a certain afternoon.
I am hoping the next generation of meteorologists will do a better job. But, for now, just get used to hearing “hot and humid with the chance of a brief afternoon shower or thunderstorm in a few spots†for the next three months. About the only thing that can really bring widespread, soaking rain is something from the tropics. And, you can bet with this ongoing drought we will be watching the Atlantic basin very closely this year.
