Mesoscale Discussion 2089

Issued

Dec 31, 2021, 12:48 PM CST (18:48 UTC)

Expired

Dec 31, 2021, 1:45 PM CST

In force

57 min

Issued by

the Storm Prediction Center

Concerning

Severe potential...watch unlikely

Chance of a watch

20%

Counties Blount County, AL, Calhoun County, AL, Cherokee County, AL, Clay County, AL, Cleburne County, AL, Etowah County, AL, Fayette County, AL, Jefferson County, AL, Randolph County, AL, Shelby County, AL, St. Clair County, AL, Talladega County, AL, Tuscaloosa County, AL, Walker County, AL, Carroll County, GA, Haralson County, GA, Polk County, GA

The Birmingham radar (KBMX), 50 km from the middle of the area, began a volume at 18:49 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

663 
ACUS11 KWNS 311848
SWOMCD
SPC MCD 311848 
GAZ000-ALZ000-311945-

Mesoscale Discussion 2089
NWS Storm Prediction Center Norman OK
1248 PM CST Fri Dec 31 2021

Areas affected...portions of northern Alabama

Concerning...Severe potential...Watch unlikely 

Valid 311848Z - 311945Z

Probability of Watch Issuance...20 percent

SUMMARY...Some increase in potential for a couple of severe storms
appears to be underway, though still a conditional/uncertain
scenario.  WW remains unlikely at this point, but evolving trends
warrant continued examination.

DISCUSSION...Latest visible satellite imagery shows a subtle
increase in convective activity across parts of north-central
Alabama at this time.  Though radar reflectivity remains weak,
lightning has now been observed, and this muted convective increase
aligns areally and temporally with persistent depiction in
successive HRRR runs of eventual, isolated supercell development
later this afternoon.  However, the HRRR is a bit of an outlier in
terms of coverage/intensity of afternoon convection, with only the
hi-res ARW window even remotely supportive of the plausibility of
the HRRR scenario.

From a synoptic perspective, weak warm advection is ongoing, near
and north of a somewhat washed-out warm front lying across northern
Alabama, which is supporting ongoing/weak showers across the
southern Appalachians.  Background short-wave ridging is apparent,
which seems likely to hinder -- or at least temper -- potential for
robust afternoon storms.  

With that said, deep-layer flow -- though a bit veered in the
boundary layer and fairly unidirectional with height -- is
contributing to 0-6km shear supportive of updraft rotation.  As
such, despite a larger-scale pattern that is somewhat inhibitive, we
will continue to monitor convective evolution for signs that the
more aggressive HRRR scenario could come to fruition -- which would
heighten prospects for WW consideration.

..Goss/Grams.. 12/31/2021

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...FFC...BMX...HUN...

LAT...LON   33328806 33838773 34368612 34118519 33678482 33078565
            32988679 33328806

Mesoscale Discussions in Alabama, 2021Mesoscale Discussions in Georgia, 2021Every mesoscale discussion in 2021

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.