Mesoscale Discussion 2071

Issued

Dec 29, 2021, 10:44 AM CST (16:44 UTC)

Expired

Dec 29, 2021, 12:45 PM CST

In force

2 hr

Issued by

the Storm Prediction Center

Concerning

Severe potential...watch likely

Chance of a watch

95%

The Memphis radar (KNQA), 129 km from the middle of the area, began a volume at 16:48 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.

• Tornado Watch 569Dec 29, 12:05 PM CST

002 
ACUS11 KWNS 291644
SWOMCD
SPC MCD 291644 
ALZ000-TNZ000-MSZ000-ARZ000-LAZ000-291845-

Mesoscale Discussion 2071
NWS Storm Prediction Center Norman OK
1044 AM CST Wed Dec 29 2021

Areas affected...portions of northeast LA...southeast AR...southwest
TN...northern MS and extreme northwest AL

Concerning...Severe potential...Watch likely 

Valid 291644Z - 291845Z

Probability of Watch Issuance...95 percent

SUMMARY...The severe thunderstorm threat is expected to increase by
18z. Supercells and bowing segments producing a few tornadoes,
damaging gusts and isolated large hail are expected with this
activity. A watch is likely by around 18z

DISCUSSION...An area of showers and isolated thunderstorms across
parts of northern MS/AL and south-central TN will continue to shift
east/northeast through early afternoon in a strong warm advection
regime. Airmass recovery in the wake of this activity is evident
across parts of northwest MS into southeastern AR where cloud breaks
are allowing for greater heating. Temperatures to the west and south
of morning precipitation generally are in the low 70s, with upper
60s to low 70s F dewpoints. This is allowing or rather quick
destabilization with MLCAPE values quickly increasing to around
500-1000 J/kg. This trend should continue with northeast extent
across the MCD area as morning precipitation continues to clear. 

A surface boundary associated with morning convection extends across
parts of southeast AR into northern MS/AL and may serve as a focus
for greater severe thunderstorms potential by early afternoon. A
couple rounds of severe storms may be possible as initial supercell
storms develop in the vicinity of this surface boundary within the
open warm sector, while additional convection spreads eastward from
AR/LA associated with the surface low and cold front. Strong
vertical shear, with effective shear magnitudes greater than 50 kt,
and a southwesterly low level jet increasing to around 40-50 kt
through the day will support supercells. A few tornadoes, one or two
of which could be strong, damaging gusts and isolated large hail is
expected with this activity. With time, convection may develop into
one or more bowing segments closer to the front/surface low. As this
occurs, the threat for damaging wind gusts will increase, with a
continued threat for mesovortex tornadoes given favorable low level
shear and rich boundary-layer moisture. A watch will likely be
needed by around 18z.

..Leitman/Hart.. 12/29/2021

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

ATTN...WFO...OHX...BMX...HUN...MEG...JAN...LZK...SHV...

LAT...LON   35348973 35458831 35178780 34868766 34448757 34208758
            33968773 33688803 32729041 32399168 32589207 32899214
            33799210 34279191 34929119 35229033 35348973

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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.