Another Threat of Severe Storms for Your Wednesday

A strong trough and associated cold front will bring showers and thunderstorms to Central Alabama starting as early as just before sunrise and will be out of the area just before your late local news. There is a threat for strong to severe storms with this system, especially from 12:00 pm to 8:00 pm across nearly all of the area with the exception of the northwestern corner. This system will affect the area in two waves with the first wave being the weaker of the two. The second wave is the one we’ll have to really watch for damaging winds up to 60 MPH, large hail up to quarter size (1-inch in diameter), and a brief tornado or two.

The above animation is the latest simulated radar run from the high-resolution NAM valid from Wednesday starting at 3:00 am and ending at 7:00 pm. A weakening band of showers and thunderstorms will begin to push into the northwestern corner of the state around 3:00 am and eventually start to move into the northwestern parts of Central Alabama around or just before 6:00 am. It will make it to the I-59 corridor around or just before 8:00 am while continuing to weaken and eventually nearly falling apart around 11:00 am.

After 11:00 am is when we’ll have to watch and see what can get going over the northwestern parts of the area, because as you can see, much of the southern and southeastern parts will not have that much activity move through and that will allow the atmosphere to recover.

As we continue to move on through the afternoon hours, more showers and storms look to form in the destabilizing air that will have a good bit of instability and will eventually become a line of potentially strong to severe storms around 4:00 pm. This line looks to continue to grow stronger as it pushes eastward before exiting the area around 8:00 pm. This model run ends at 7:00 pm as that is the end of the 60-hour forecast period for the high-resolution NAM.

The above image is the wind shear around 4:00 pm and we see that a low-level jet will be moving over the I-59 corridor with winds topping out around 70-75 knots. Wind shear is the change in the wind throughout a certain height range, which for this image is set from ground-level to 6 km up in the atmosphere. Supercells are usually associated with shear values of 35-40 knots and greater at this height lever.

This image is the instability at 4:00 pm, also known as convective available potential energy, or CAPE. It shows the total amount of potential energy (or fuel for the storms) available for air parcels rising from the surface to the free convection height. Values of 500-1500 J/kg are considered moderately unstable, 1501-2500 J/kg is strongly unstable, and anything greater than 2500 J/kg is considered extremely unstable. Much of the instability for along and north of the I-59 corridor is less than 500 J/kg while south of that, we see values reaching 2000 J/kg.

These values show that there will be a threat of strong to severe storms with damaging winds and large hail being the main focus, but a brief tornado or two will be possible as well, just on a much lower threat level.

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