SPC Upgrades Severe Weather Risk

The Storm Prediction Center upgraded the severe weather risk for the northern half of Alabama for this afternoon and tonight from MARGINAL to SLIGHT.

Here is an excellent graphic explaining the different risk tiers:

THOUGHTS ON THE THREAT
…Available moisture for this event is limited. Dewpoints will only be in the middle 50s, which is marginal for severe weather at best.
…Instability will be limited as well, with CAPE values generally between 500-1,000 joules/kg. It will be actually increasing a bit however between 6-8 p.m. for areas along and south of I-20.
…And the main concern is that low level wind fields will be increasing after 6 p.m. in the lowest 5,00 feet of the atmosphere. This will lead to increased speed shear for thunderstorm organization and they should become stronger between 7-10 p.m., first over western counties and spread across all of Central Alabama between 7-10 p.m.
…We will actually be in the left front quadrant of a moderate upper level jet which will be blowing at over 100 mph at 30,000 feet. This will also help the storms strengthen.
…The low level helicity for tornadoes is expected to be low however, so the main threats will be hail and damaging winds. SIGTOR values are less than 1, which is low for significant tornado potential.
…The atmospheric profile will feature cold temperatures aloft that will help enhance the instability slightly and help hail formation. The low level wind field increase will enhance the damaging wind threat as well.

This is what the radar might look like around 9 p.m. tonight according to the HRRR model.

TIMING
…Expect a broken line of storms to move into western Alabama between 6-7 p.m.
…Additional storms will develop rapidly through the I-59 Corridor between 7-8 p.m.
…Jasper/Fayette/Cullman will see strong to severe storms between 7-9 p.m.
…Tuscaloosa/Birmingham areas will see strong to severe storms between 8-10 p.m.
…Areas from Clanton to Anniston will be impacted between 9-11 p.m.

We will have frequent updates through the afternoon and evening as the event unfolds.

Category: Alabama's Weather, Severe Weather