Wednesday is shaping up to be the first significant severe weather and high-impact tornado threat for Dixie Alley and the Mid-South. A potent upper level storm system will approach the region, allowing a surface low to develop and intensify, pulling in deep moisture and warm air into the region.
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With the increased moist and warm airmass at the surface, and colder air moving over the region with the approaching upper-level storm system, the Convective Available Potential Energy (CAPE) will be high in the Mid-South and Dixie Alley. The higher the CAPE values, the more unstable the atmosphere; thus, producing stronger updrafts, leading to more severe weather possibilities.
The approaching upper-level storm system will provide favorable wind speeds and directions across the region. Winds will change directions and speed with height, which provides a favorable environment for severe thunderstorms and tornadoes. This is known as directional and speed shear. Directional shear is wind direction changing with height while speed shear is the change in wind speeds with height.
Strong vertical wind shear is crucial for the development and longevity of severe thunderstorms, and wind shear looks favorable for severe thunderstorms late-Wednesday. From 500 mb (around 18,700 feet) down to 925 mb (around 2,500 feet), the winds change direction and speed, which suggests severe thunderstorms and tornadoes are possible with other favorable atmospheric parameters.
The aforementioned setup indicates not only significant severe weather is possible but tornadoes are also possible late-Wednesday. When looking at such a setup, it is important to look dive into the history and look at similar weather patterns in the past and investigate what they have produced. This is known as analogs.
Looking at the analogs, they indicate similar atmospheric events in the past have led to strong, long-track tornadoes across the region, so this event needs to be monitored closely! It should be noted: this is still far out so the specifics cannot be identified at this point but that will be ironed out over the coming days.
This is supported by the significant tornado parameter values Wednesday afternoon across the region. The significant tornado parameter is a complex composite index, consisting of multiple ingredients. It factors in 0-6 km bulk wind difference (6BWD), 0-1 km storm-relative helicity (SRH1), surface parcel CAPE (sbCAPE), and surface parcel LCL height (sbLCL). To put this in laymen terms, it’s a great tool to identify where strong tornadoes may occur. High significant tornado parameter values are forecast to be present, which suggest tornadoes, some strong or violent, are a possibility across parts of western Tennessee, Mississippi, and western Alabama.
While there are considerable questions surrounding this event, it appears thunderstorms will develop early-Wednesday west of the Mississippi River in Arkansas and Louisiana. These storms will move east through Wednesday afternoon into Wednesday evening for areas east of the Mississippi River, including Tennessee, Mississippi, Alabama, and eventually Georgia, and the Florida Panhandle.
Due to the severe potential, the Storm Prediction Center has highlighted the Mid-South and Mid-Mississippi Valley for severe weather Wednesday. A Level 3 risk for severe weather is in place Wednesday for the red shaded area. This includes southwestern Tennessee, eastern Arkansas, northeastern Louisiana, Mississippi, and Alabama. A Level 2 and Level 1 risk surrounds the Level 3 risk in the orange and yellow shaded areas.
Now is the time to prepare! Do not panic but have a plan in place in case a Tornado Watch or Tornado Warning is issued for your area. Make sure you have a few reliable sources to receive weather information from as this event approaches.
It is also a good time to refresh your memory on tornado terminology. A tornado watch means conditions are favorable for tornadoes to form. A tornado warning means a tornado has been indicated or spotted. A tornado emergency means a severe threat to human life and catastrophic damage to property is likely.