1/21 - 11pm - Severe Weather Outbreak Possible Tomorrow

A line of strong storms moved through West Tennessee this morning, but what's on the way for tomorrow evening could be even more potent with the potential for damaging winds and tornadoes. Check out my broadcast from this morning below to see what all this means and then continue on below the video for a detailed severe weather breakdown:

Timing and Threats

The Storm Prediction Center has issued a Slight Risk with a 30% hatched area for tomorrow's severe weather event from Mississippi to Indiana. The main time frame for these storms to roll through West Tennessee and Mississippi will be from 5pm tomorrow to 3am Monday. This does not mean ten straight hours of storms in any one location, but rather a ten hour window where storms will be affecting the region. Wind damage and hail will be the most common threats, but this could also be a significant tornado event. Some individual supercells or cell clusters may form ahead of a main QLCS (squall line) of storms late tomorrow afternoon and evening. These front-running storms, should they form, would be the ones with the highest tornado risk, but both the line of storms and the individual cells could produce a significant tornado or two. The SPC's wording on their Slight Risk outlook is fairly strong:

AN APPRECIABLE SEVERE EVENT IS POSSIBLE ACROSS THE REGION SUNDAY NIGHT/EARLY MONDAY...INCLUDING THE POTENTIAL FOR TORNADOES AND DAMAGING WINDS. AN UPGRADE TO A CATEGORICAL MODERATE RISK MAY BE WARRANTED IN SUBSEQUENT OUTLOOKS FOR PORTIONS OF THE REGION.

Setup

The setup for tomorrow's severe weather event is fairly classic. A large trough will be moving through the region providing increased wind speed aloft, which increases instability and provides wind shear. This trough will also be negatively tilted, meaning the axis or tightest gradient of the trough will be leaning from southeast to northwest as you see in the graphic to the right from the 0z NAM model. This negative tilting further increases wind shear because the upper level winds take on a more southerly component rather than a southwesterly one.

Not only will we have wind shear between the surface and aloft, but also the surface and the low levels of the atmosphere too. This low-level shear is essential for tornadoes to form and for storms to overcome low levels of instability. The NAM output has quite a bit of low-level shear from Mississippi all the way to Kentucky, so that's a pretty good indication that rotating storms and tornadoes will be possible during the duration of this event tomorrow.

The amount of moisture that will be surging up from the Gulf of Mexico while the region is in the warm sector of this system is going to be tremendous. The current dewpoint in Starkville, Mississippi is 41 degrees, but by tomorrow evening we'll be in the 60's. That is certainly enough moisture to supply the atmosphere with the needed instability for severe weather.

When you put together these factors plus the idea that we may have CAPE (instability) values over 1000 J/kg, you get a fairly decent tornado risk. The Significant Tornado Parameter exceeds 2 on the 21z SREF model at 9pm and midnight (1/23) tomorrow and has been fairly consistent on the last few runs of the SREF. This is not "off the charts" or anything like that, but it's enough to raise eyebrows. As stated above, both individual cells and the main QLCS line of storms could produce strong tornadoes. The QLCS will be especially difficult because there could be embedded supercell structures within it that produce tornadoes like an individual supercell would. I still think the highest tornado risk will be in Northeast Mississippi (Starkville, West Point, Columbus, Tupelo, Corinth, etc.), but the latest indications like the STP above are pointing toward that threat leaking over into southern portions West Tennessee as well.

I'll be updating my Twitter, Facebook, and Google+ accounts all day tomorrow as these storms roll through, so be sure to follow or friend me for the latest information.