March 22-23 Severe Weather Update

23 03 2013

We pretty much have the forecast wrapped up as all the models are agreeing with pretty much everything. We will first start off with the overall setup of where the low will wind up moving.

Right now the surface low is sitting near Houston, TX. SPC has a warm/stationary front along the Gulf Coast. There is a strong temperature gradient in Central Mississippi and Alabama which is where the low pressure will move along. The low pressure should enter Southwest Mississippi late this evening around 10PM and slowly move into West Central Alabama near 2AM Sunday morning. The low should strengthen some and make its way into Central Tennessee near 8AM. At this time it will hang out in Tennessee for a little bit and strengthen the cold front which will start sweeping through Alabama near 4PM tomorrow. The cold front should pass through Alabama by 10PM tomorrow night.

Now time for the setup of the threats. Right now, there is a tornado watch in Central Mississippi and a severe thunderstorm watch in North Mississippi stretching into Southeast Arkansas and Northeast Louisiana. This makes perfect sense with the current forecast track of the low. As the low makes its movement to the Northeast it will bring with it warm, moist, unstable air along the coast which would be favorable for severe thunderstorms that could produce hail, some possibly large, and damaging winds, but about a mile above us in the atmosphere is a key wind called Low Level Jet that is very weak until tonight when it usually strengthens. Here is the situation with that though, the area where the Low Level Jet or LLJ strengthens will be north of where the rich, unstable air is. The LLJ is a key component for tornadoes to develop as long as everything else is there for the storms. So southern Mississippi and Alabama will have the unstable air while northern Alabama will have the LLJ and a component we call shear which is a difference in wind speed and direction in the atmosphere. This leaves Central Alabama and Central Mississippi which will likely have a mix of the two which is where the main focus is. Now this isn’t to say that southern Alabama and northern Alabama are in the clear as mentioned earlier.

Finally to the threats and the areas. The biggest threats at first will be damaging wind and hail through the rest of today. Once when the LLJ kicks in that will increase the threat of tornadoes. The area for the threat of damaging wind and hail will be our entire viewing area and as the night goes on into the morning the threat of tornadoes shows up for Central Alabama all the way down to the Florida/Alabama state line. Parts of Northern Alabama have a chance as well, but it is lower than the rest of Alabama. This threat does stretch into western Georgia. The timing of all of this is hard to tell, but the tornado threat will be after midnight.


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