The Storm Prediction Center outlines a risk of severe storms for all of Alabama and Middle Tennessee for Wednesday. The timing for North Alabama and Southern Middle Tennessee looks to be from as early as 5 PM in The Shoals to as late as 2 AM near the Georgia border.
- Expect gusty winds in the afternoon and evening that could top 30 miles per hour (wet ground means trees could fall in that breeze).
- The squall line’s speed will determine how much rain you get: 1-2″ in less than one hour. causing rapid rises in ‘flashy’ waterways.
- Severe wind gusts over 58 mph and tornadoes are the primary threats.
Before the storms
Cloudy skies and a cool morning will give way to a warmer and breezy afternoon and evening as a warm front lifts north through the Tennessee Valley. Winds this afternoon and evening outside of thunderstorms could gust to 30 mph. We could see some wind gusts knock down trees well ahead of the storms due to the soggy, saturated ground.
What to expect as the storms approach (5 PM Wed. to 1 AM Thu.)
This will be a line of heavy storms: a ‘squall line’ (or sometimes referred to as a QLCS). Storms along the line could produce one or more of three things to qualify them as ‘severe:’ wind gusts over 58 miles per hour, hail larger than a quarter, or a tornado.
The risk of a tornado often gets the most focus and creates the most anxiety, but the stiff breeze ahead of the front and the stronger, gusty winds within the storms could knock down a lot of trees because of the soggy ground.
- 6PM to 9PM A line of intense thunderstorms moves out of Mississippi (and across West Tennessee) into Wayne, Lauderdale, Colbert, Franklin, Marion, Winston, Lawerence (AL & TN), Limestone, and Giles Counties. Expect a gusty south wind ahead of the line, and individual thunderstorms within the line could produce strong ‘damaging’ winds, hail, flash flooding and tornadoes. The slow movement of this line in Northwest Alabama probably causes some localized flooding with more than 1-2″ of rainfall in that three-hour window.
- 8PM to 11PM: The line of storms moves through Decatur, Huntsville, Madison, Athens, Arab, Fayetteville and Cullman. The storms may be at peak intensity around 7 to 8 PM as they begin moving a little faster toward the east. Tornadoes and strong winds will be possible from individual storms in the line; some small hail may develop as well, but the loss of daytime heating could reduce the threat of hail somewhat after 9 PM. Some flash flooding is possible with rainfall totals of 1-2″ in less than 2 hours.
- 10 PM to 1 AM: Storms are still rumbling but likely a little weaker in Northeast Alabama where the fuel (instability isn’t as strong). Expect heavy rainfall, gusty winds, and a limited threat of a severe wind gust or tornado through 1 AM in northeastern Alabama.
Flash Flood Threat
The National Weather Service in Huntsville (as well as neighboring offices in Nashville and Birmingham) posted a Flash Flood Watch for all of North Alabama (Central Ala. and Middle Tenn.) through early Thursday.
The Weather Prediction Center (WPC) has upgraded northwestern Alabama and Middle Tennessee to a MODERATE RISK of flash flooding for Wednesday night.
Locally-heavy rainfall adding up to around 1 to 2 inches in less than two hours could cause rapid rises of water on ‘flashy’ creeks and streams (those that typically rise and fall quickly in heavy rain). The timing for the flash flood threat is aligned with the severe weather threat.