Risks and Timing
The Storm Prediction Center has outlined a Moderate Risk area for severe weather tomorrow in an expansive area of the South. This includes a 15% tornado risk. Storms will likely erupt early this morning as a warm front surges northward and bring a hail risk to West Tennessee while not-as-strong storms will affect the most of the remainder of Kentucky, Tennessee, and Mississippi. These storms shouldn't be a huge deal, but a few might reach severe limits.
A brief break in the action throughout the mid and late morning hours should provide enough recovery time for the atmosphere to recharge and re-fire storms around noon. These storms will try to get going in West Tennessee and Northeast Arkansas, but will gain strength as they hit areas of greater surface heating to the east. These are the storms that could be very bad in a lot of areas. The worst tornado threat throughout the afternoon will be in Central Kentucky and Middle Tennessee, but there's a secondary area that could have tornado problems in Northeast Mississippi into North Alabama if a little more low-level wind shear comes into play. The Storm Prediction Center's latest severe weather outlook seems to pick up on that secondary tornado risk area by extending the Moderate Risk down to East Mississippi and Alabama. Straight-line wind damage and hail will be possible throughout the South tomorrow, so even if you're not in an area where tornadoes will be likely you need to be on the lookout for severe storms. The storms should move out quickly tomorrow evening once the cold front accelerates southeastward through the region.
The reason why Central Kentucky to Middle Tennessee will be the area for maximum tornado potential tomorrow is because of an alignment of a few factors. For one, the fastest upper-level winds will be centered right over this area tomorrow afternoon. When you couple that with almost southerly winds (may be a bit southwesterly at times), you get not only a high difference between wind speed aloft and at the surface, but also a difference in direction. This is called wind shear and it's crucial to sustaining a thunderstorm and allowing it to become strong enough for tornado development. The southerly winds at the surface will help what's called low-level wind shear, and that's usually a pretty big factor in who gets tornadoes.
These southerly winds will also be bringing in moist air from the Gulf, which is the fuel for these storms as they develop. While the best moisture will be over Mississippi, Alabama, and Tennessee tomorrow, it will still be ample for serious severe weather in Kentucky. This moisture will bring some serious atmospheric instability to the region. When you couple this instability with helicity (the tendency for the atmosphere to rotate), you get what's called the Energy Helicity Index (EHI). This is a decent indicator of where the best tornado ingredients will be, and as you can see on the left, the values are particularly high tomorrow across a pretty vast area from Mississippi through Kentucky. Supercells appear likely in Tennessee and Kentucky, but Northeast Mississippi may have more of a mixed supercell/squall line of storms scenario due to less wind shear. This could be an entirely linear squall line event across Northeast Mississippi/North Alabama tomorrow if wind shear under performs. While squall lines don't harbor as many strong tornadoes, it is still a very real threat that needs to be monitored.
Before severe weather
- Make sure your cell phone is charged in case you lose power
- Have flashlights with fresh batteries ready to go. Your cell phone should NOT be your primary flashlight
- Your NOAA Weather Radio/Cell phone alert app should be ready to alert you
- Make a central meeting location for family members should you lose communications after the severe weather passes
When a Tornado Warning is issued for your area
- Get to the lowest level of your home, apartment, or office
- Stay away from windows and try to get to the center of the structure you're in
- Evacuate mobile homes and get to a safe, sturdy building immediately
- Make sure you are wearing sturdy shoes
- If you have time (have these ready to go before a warning is issued), put bicycle helmets on the kids and yourself. Quite a few deaths were caused by head trauma in last year's tornadoes.