Mesoscale Discussion 1978

Issued

Dec 10, 2021, 1:35 PM CST (19:35 UTC)

Expired

Dec 10, 2021, 3:45 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), 145 km from the middle of the area, began a volume at 19:39 UTC, the scan nearest the moment this went out.

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• Tornado Watch 552Dec 10, 3:00 PM CST
• Tornado Watch 553Dec 10, 5:20 PM CST

420 
ACUS11 KWNS 101935
SWOMCD
SPC MCD 101935 COR
ILZ000-TNZ000-KYZ000-MOZ000-ARZ000-102145-

Mesoscale Discussion 1978
NWS Storm Prediction Center Norman OK
0135 PM CST Fri Dec 10 2021

Areas affected...Much of central and northeastern Arkansas through
southeastern Missouri and adjacent portions of southern
Illinois...western Kentucky and Tennessee

Concerning...Severe potential...Watch likely 

Valid 101935Z - 102145Z

CORRECTED FOR TYPO

Probability of Watch Issuance...95 percent

SUMMARY...Discrete supercell development appears increasingly
probable by 4-6 PM CST, accompanied by the risk for severe hail and
tornadoes, including increasing potential for a couple of strong
tornadoes by early evening.

DISCUSSION...A short wave impulse of subtropical eastern Pacific
origin continues to accelerate northeastward across Kansas and
Oklahoma, and is forecast to reach the mid/lower Missouri Valley
vicinity by early evening.  Mid/upper forcing for ascent and
elevated moisture return preceding this feature have contribute to
weak high-based convection and light rain in a corridor across
eastern Oklahoma into the lower Missouri Valley, while low-level
moisture from the Gulf of Mexico gradually deepens across the lower
Mississippi Valley into parts of the southeastern Great Plains.  The
deeper low-level moisture return is being aided by a branch of
stronger southerly flow across the northwestern Gulf coast vicinity
into the Ozark Plateau.  This appears to include a 40-45 kt speed
maximum around 850 mb, across the upper Texas coastal plain into the
Ark-La-Tex vicinity.

Through 21-00Z, model output continues to generally indicate that
this speed maximum will rapidly propagate northeastward into the
Ozark Plateau through middle Mississippi/lower Ohio Valley vicinity,
while strengthening to 50+ kt in a corridor from near Little Rock AR
into the Missouri Bootheel vicinity.  It appears that deepening
boundary-layer moisture and increasing mixed-layer CAPE along this
corridor will coincide with weakening inhibition associated with a
transition from broadly anticyclonic to cyclonic mid-level flow. 
This is expected to allow for the initiation of at least scattered
discrete storm development, as southwesterly flow in the 700-500 mb
layer also strengthens to 60-80+ kt.

This regime likely will become increasingly conducive to the
development of supercells, with the potential to produce severe hail
initially, along with at least some risk for tornadoes.  Backing of
surface winds toward a south to south-southeasterly component by 00Z
may gradually contribute to enlarging, clockwise-curved low-level
hodographs increasingly conducive to tornadoes, a couple of which
may become strong.

..Kerr/Thompson.. 12/10/2021

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

ATTN...WFO...PAH...MEG...LSX...LZK...SGF...

LAT...LON   36769201 38068994 37408898 36288919 34749081 34519233
            35259322 36769201

Mesoscale Discussions in Arkansas, 2021Mesoscale Discussions in Missouri, 2021Mesoscale Discussions in Illinois, 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.