A dangerous multi-day severe weather outbreak is ramping up across the southern United States at this hour, with a powerful squall line stretching from St. Louis to the Gulf of Mexico. Millions of people are at risk for widespread wind damage, large hail, and even tornadoes.

A moderate risk for severe weather is in effect for parts of the Deep South and Mississippi River Valley, including both Jacksons (Tenn. and Miss.) as well as Tupelo and Memphis. A moderate risk is a 4 on a scale from 0 to 5. A slight risk—a 2 out of 5—is in effect for a much larger area, and appears in yellow on the map above.

Today's severe weather outbreak will come in two batches. The main catalyst for the powerful storms will be a strong cold front sweeping through the middle of the country. A severe squall line has already developed along the leading edge of the cold front, bringing with it a risk of widespread wind damage from gusts of 60 MPH or greater. Ahead of the cold front, discrete storms are developing and carry the greatest risk of large hail and tornadoes.

At 1:30 PM CDT, a mess of tornado watches was in effect along and east of the Mississippi River from St. Louis to the Gulf of Mexico. Today's risk for tornadoes in this area is 150 times higher than climatologically normal.

(Today's climatological risk for tornadoes in this area is 0.10%—a 15% risk divided by 0.10% climatological odds of seeing a tornado nearby on October 13 = a risk of tornadoes 150 times higher than normal).

The one-two punch of the storms is very well simulated by the HRRR weather model. Below is a simulated radar image for today at 6:00 PM CDT:

The model—which does a really good job at predicting the intensity and location of thunderstorms—shows a powerhouse squall line moving east from Illinois to Louisiana, with discrete storms forming in Alabama out ahead of the main activity.

This morning's run of the NAM 4km weather model shows the squall line reaching Cincinnati, Knoxville, and Atlanta early tomorrow afternoon.

In anticipation of severe storms continuing through the night tonight and into the day tomorrow, the Storm Prediction Center has issued a slight risk of severe weather from the eastern edge of today's risk east through the Carolinas:

Severe thunderstorms that occur during the nighttime and early morning hours are the most dangerous since people are asleep and often receive little or no advanced warning of potential hazards. One person has already died from this round of storms due to this very reason. THV 11 reports that an Arkansas man was killed when storm debris damaged his house this morning.

Pay attention to forecast outlets this afternoon if you're in the path of the severe weather, and take special care to ensure that you can receive severe weather warnings tonight while you're asleep. Many smartphones are now equipped with wireless emergency alert system capabilities to alert you in case a tornado warning is issued for your location.

The Storm Prediction Center issues severe weather forecasts and watches, while local National Weather Service offices are responsible for issuing warnings for individual storms.

[Images: outlook maps by the author, weather model images via WeatherBELL]

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