There is Still a Severe Weather Threat for West Central Alabama
We continue to monitor an intensifying surface low over eastern Mississippi that is moving north-northeast toward western Alabama.
Storms that form to the east and southeast of this low will have sufficient bulk shear to allow them to organize.
Instability is rising across the area, with CAPE values between 250-750 joules/kg over Sumter and Marengo Counties. Bulk shear values are 40-50 knots across that area, allowing for the storm organization. In addition, 0-1 km storm relative helicity is running 300-400 m2/s2, so if any organized updrafts get going, then there could be a few brief tornadoes.
The SPC does not believe that there is a sufficient threat to warrant a tornado watch at this time.
There just issued a mesoscale discussion. Here is the text of it:
Mesoscale Discussion 0283
NWS Storm Prediction Center Norman OK
0358 PM CDT Sun Apr 22 2018
Areas affected…West-central Alabama
Concerning…Severe potential…Watch unlikely
Valid 222058Z – 222330Z
Probability of Watch Issuance…20 percent
SUMMARY…A marginal tornado threat and a few strong wind gusts will
be possible across parts of west-central Alabama late this
afternoon. The threat is expected to remain localized and weather
watch issuance appears unlikely.
DISCUSSION…The latest surface analysis shows a deepening 1008 mb
low across eastern Mississippi. Winds are backed at the surface to
the east of the surface low across most of Alabama. A moist airmass
extends northward into central Alabama where surface dewpoints are
in the mid to upper 60s F. Although little surface heating has taken
place in central Alabama, the RAP suggests that weak instability is
present. This combined with strong large-scale ascent associated
with a shortwave trough evident on water vapor imagery, will support
surface-based thunderstorm development over the next couple of
hours. The WSR-88D VWP at Birmingham shows a looped hodograph with
0-6 km shear at 55 kt and 0-1 km shear near 40 kt. This should be
sufficient for storm rotation within the stronger discrete cells. As
a result, a marginal tornado threat will be possible late this
afternoon. A few strong wind gusts may also occur.
..Broyles/Hart.. 04/22/2018
Category: Alabama's Weather, ALL POSTS