Alert archive / Alabama / Mesoscale Discussions in 2021

Mesoscale Discussion 1942

November 11, 202112 counties in Alabama

The Storm Prediction Center issued this mesoscale discussion at Nov 11, 2021, 12:08 PM CST for 12 counties in Alabama. It was in force for 2 hr.

The area

The outline as issued.

The facts

Issued
Nov 11, 2021, 12:08 PM CST (18:08 UTC)
Expired
Nov 11, 2021, 2:15 PM CST
In force
2 hr
Issued by
the Storm Prediction Center
Concerning
Severe potential...watch unlikely
Chance of a watch
5%

Counties Bibb County, AL, Chilton County, AL, Choctaw County, AL, Clarke County, AL, Dallas County, AL, Hale County, AL, Jefferson County, AL, Marengo County, AL, Perry County, AL, Shelby County, AL, Tuscaloosa County, AL, Wilcox County, AL

The radar

The Birmingham radar (KBMX), 92 km from the middle of the area, began a volume at 18:09 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.

The nearest sounding before it

Birmingham, AL (KBMX), launched 12:00Z, 6.1 hours before the alert went out and 92 km from the middle of its area. This is the routine balloon launch nearest before it, the air the forecaster had in hand, not a measurement taken for the alert.

Skew-T log-pSkew-T log-p diagram, Birmingham, AL at 12:00Z on 2021-11-11Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 0 joules per kilogram.LCL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed.
HodographHodograph, Birmingham, AL at 12:00Z on 2021-11-11The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 215 square meters per square second.19395878Sfc1 km3 km6 km9 kmRMLM
The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km.
Mixed-layer CAPE
0 J/kg
Mixed-layer CIN
No buoyant parcel
Mixed-layer LCL
1054 m above ground
0-6 km bulk shear
53 kt
0-1 km storm-relative helicity
215 m²/s²
0-3 km storm-relative helicity
208 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.0

Open this sounding in Storm Lab

The text

As transmitted.

383 
ACUS11 KWNS 111808
SWOMCD
SPC MCD 111808 
ALZ000-MSZ000-112015-

Mesoscale Discussion 1942
NWS Storm Prediction Center Norman OK
1208 PM CST Thu Nov 11 2021

Areas affected...central into southwest AL

Concerning...Severe potential...Watch unlikely 

Valid 111808Z - 112015Z

Probability of Watch Issuance...5 percent

SUMMARY...A localized risk for damaging gusts may materialize over
the next couple of hours.  The coverage/intensity of gusts will
preclude a severe thunderstorm watch issuance.

DISCUSSION...Radar mosaic shows a developing squall line over
west-central AL extending south-southwestward into east-central MS
as of 12pm (18 UTC).  The airmass ahead of the developing convective
line continues to heat/destabilize with 250-500 J/kg MLCAPE
estimated per modified 12z NAM forecast soundings.  It is noted that
the RAP/SPC mesoanalysis is under-forecasting CAPE due to a too-dry
depiction of the boundary layer with surface dewpoints 3-5 degree F
too cool compared to observations.  Surface to 2-km lapse rates have
steepened considerably (near 8-9 deg C/km).  Given the wind profile
supports storm organization, a couple of strong and possibly
damaging gusts are plausible as the squall line moves eastward
across central AL through mid afternoon.

..Smith.. 11/11/2021

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

ATTN...WFO...BMX...MOB...

LAT...LON   31768852 33598744 33698664 33448625 32098697 31598772
            31768852

Nearby

Mesoscale Discussions in Alabama, 2021Every mesoscale discussion in 2021

Sources

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.