By Jim Stefkovich, Meteorologist, Alabama Emergency Management Agency
CLANTON – April 13, 2018, 8:50 a.m. – Meteorologists depend on computer models to develop forecasts. When the models are in good agreement, confidence is high. Unfortunately, for this weekend’s event, confidence is low as far as timing, but consistent in that a potent line of thunderstorms will affect much of the state from Saturday through early Sunday morning. Thus, this will likely be a long duration event.
Forecast models are honing in on two scenarios. One is the line of storms will move into northwest AL predawn and make its way near the I20/59 corridor by late morning or early afternoon before stalling. It will then wait for additional upper level support to push it eastward late in the afternoon or evening. In this scenario, severe weather would occur along the leading edge in the morning, with severe weather during the late afternoon and overnight over the southern 2/3 of the state.
Other models are much slower in bringing the line into AL around noon on Saturday. In this case, the atmosphere would have time to become much more unstable, and the severe threat would increase dramatically. If the slower solution occurs, supercell thunderstorms/tornadoes could develop ahead of the line. This would bring a damaging wind threat from both supercells and the line of storms.
Don’t get hung up on the Storm Prediction Center’s exact locations for enhanced versus slight risk areas in the graphic above. These will likely change in updated forecasts. Just know the entire state has a threat of severe weather.
I have included a statewide timing graphic that takes both potential scenarios into account. This is why there is such a large timing block for each area. Actual severe weather will not occur for the entire time period for any one section of the state.
Rainfall of 2-4 inches will be common for areas near and west of I65, but widespread flooding issues are not anticipated. Still, if the line stalls over urban areas, some flash flooding could occur.
If you haven’t developed a severe weather action plan yet, or if it’s been awhile since you’ve looked it over, go to the following link, which provides great information. https://www.ready.gov/severe-weather. Make sure you have at least two ways to receive warning information for your location, and can wake you up if you are asleep.
With so many outdoor activities this weekend, keep in mind weather conditions can change rapidly. Make sure you stay in tune with this event, no matter where you are!