Large parts of Louisiana, Southern Arkansas and Western Mississippi are forecast to be under the pump with a localised tornado outbreak expected during Saturday (local time). Above image via the Storm Prediction Center showing a categorical Moderate Risk area which could be upgraded to a “High” risk during Saturday’s outlook’s.
A low pressure system is forecast to move North East across Texas and through Arkansas into Missouri and the Ohio Valley region. This low is expected to have a strong surface trough extending out to the East from it which will combine with a vigorous upper level system and potent moisture injection through areas South East of the system across Louisiana, Eastern Texas, Arkansas and eventually Mississippi, Alabama and surrounding States during Saturday and into Sunday. This combination is likely to produce potent instability and very strong wind shear which will essentially mean almost every cell that develops could become a supercell quickly.
Quote from the Storm Prediction Center: “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.”
Models are keen on activity developing over Far Eastern Texas early in the afternoon before moving into Louisiana where activity is forecast to strengthen. This is where it gets ugly. Looking deeper into models, it appears as though a line of potent supercells are expected to move East across Louisiana and Southern Arkansas in the South East quadrant of the low. Wind shear will allow virtually all of these cells to become tornado warned with a “likely” risk of several tornadoes occurring across Louisiana and Southern Arkansas, and some of these almost likely to become strong and long lived. There is every chance that this could end up being a very localised major tornado outbreak across the region. As a result of that, there is every chance that the Storm Prediction Center “could” upgrade to a high risk which is fairly rare – only one or two happen per year at the absolute most.