Louisiana, Arkansas, Mississippi brace for severe weather outbreak

Their words, not mine.

That said, severe weather is looking more and more likely at this point for portions of Louisiana, Arkansas and Mississippi. The change? Not much has changed in the model data – just a slight drift to the southeast. But, the “big news” I suppose is that the Storm Prediction Center has shifted the Moderate Risk to the southeast a bit to include more of Mississippi.

But what does that mean for the overall forecast? Not as much as you may think.

The Updraft Helicity streaks are still split – some models say there will be many chances for stronger storms, while others say not so much. Recall, that Updraft Helicity is used as a good indicator for identifying where some of the stronger storms will be.

But notice that the streaks have shifted from previous model runs. That shift is likely part of the reason the SPC decided to shift the Risk areas southeast, too.

I still think the forecast I put out yesterday will hold.

FROM THE SPC:

…THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF FAR EAST TEXAS…LOUISIANA…FAR SOUTHEAST ARKANSAS AND WEST-CENTRAL MISSISSIPPI…

…SUMMARY…
Numerous severe thunderstorms capable of producing tornadoes, wind damage and large hail, are expected across parts of east Texas, Louisiana, southern Arkansas, Mississippi, western Alabama and surrounding areas today and tonight.

…East Texas/Louisiana/Southern Arkansas/Mississippi/Western Alabama…
A vigorous upper-level trough will move across the southern Plains today as a mid-level jet rounds the base of the system. At the surface, a low will move into the Arklatex with a moist airmass in place to the southeast of the low across east Texas, Louisiana and western Mississippi. Surface dewpoints in the moist sector should be in the upper 60s and lower 70s F by late morning. Thunderstorms should be ongoing across north-central into northeast Texas at the start of the period. This convection with a hail threat, is likely to move into the Arklatex by midday. Further south across southeast Texas into Louisiana, the airmass should become moderately unstable and remain primarily undisturbed. In response to the approach of the upper-level trough, a low-level jet is forecast to move into far eastern Texas and western Louisiana during the early afternoon. Thunderstorms should initiate to the northwest of the low-level jet on the northern edge of the stronger instability. Strong deep-layer shear profiles will favor supercell development. Supercells will have a potential for large hail in the early afternoon. The more dominant storms could produce 2-inch diameter hailstones. As the upper-level trough approaches and the exit region of a progressive mid-level jet moves into southeast Texas during the early afternoon, surface-based thunderstorms should rapidly initiate and move eastward into western Louisiana.

RAP forecast soundings across the moist sector at 21Z from Monroe, LA southward to Alexandria, LA show MLCAPE values in the 2000 to 2500 J/kg range. Deep-layer shear is forecast to steadily increase due the approach of the mid-level jet with forecast soundings showing 0-6 km shear of 50 to 60 kt by late afternoon. This combined with strong low-level shear will be favorable for supercells and tornadoes across the moderate risk area. 0-3 km storm-relative helicities are forecast to be in the 350 to 450 m2/s2 range supporting strong tornadoes with the more dominant supercells near the axis of the low-level jet. A potential for long-track tornadoes will be possible and a regional outbreak of tornadoes could occur across parts of the moderate risk area. By early evening, the cluster of severe storms is forecast to move into southwestern and central Mississippi where a potential for strong tornadoes will continue. However, the wind-damage threat may become the more dominant hazard as the convection moves further to the east where instability is forecast to be weaker.

Further updates will need to be monitored. For my South Mississippi readers, I think this forecast still holds

Here is a quick look at the timeline for the severe weather threats Saturday and into Sunday….

More details coming up tonigth onthe news! pic.twitter.com/ZcNXS4mzVT

— Nick Lilja (@NickLilja) April 12, 2019

For more info on the threat, yesterday’s forecast still holds a fair amount of weight, even with the new data coming in… You can find that here