Mesoscale Discussion 154

Issued

Mar 11, 2021, 1:26 PM CST (19:26 UTC)

Expired

Mar 11, 2021, 4:00 PM CST

In force

3 hr

Issued by

the Storm Prediction Center

Concerning

Severe potential...watch unlikely

Chance of a watch

20%

The Paducah radar (KPAH), 84 km from the middle of the area, began a volume at 19:27 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.

999 
ACUS11 KWNS 111927
SWOMCD
SPC MCD 111926 
KYZ000-INZ000-ILZ000-MOZ000-112200-

Mesoscale Discussion 0154
NWS Storm Prediction Center Norman OK
0126 PM CST Thu Mar 11 2021

Areas affected...Parts of southeastern Missouri...southern
Illinois...southern Indiana and adjacent portions of western
Kentucky

Concerning...Severe potential...Watch unlikely 

Valid 111926Z - 112200Z

Probability of Watch Issuance...20 percent

SUMMARY...Strong thunderstorm activity may continue to develop, with
some further intensification possible through 3-5 PM CST.  Some of
these storms may be accompanied by hail and strong surface gusts
which could occasionally approach or exceed severe limits.  The need
for a watch is not currently anticipated, but trends will be
monitored.

DISCUSSION...Thunderstorm development appears to be gradually
increasing near the immediate vicinity of the slowly southward
advancing surface front, south of the Interstate 44/64 corridors of
southeastern Missouri into southern Illinois.  This appears to be
aided by inflow of air from a weak destabilizing boundary layer
(CAPE on the order of 500 J/kg) into a zone of weak lower/mid
tropospheric warm advection. 

This is occurring in the wake of the significant short wave trough
accelerating east-northeastward through the lower Great Lakes/upper
Ohio Valley vicinity, where general rising mid-level heights may
tend to suppress convective development late this afternoon. 
However, it is possible that the ongoing activity is being supported
by a subtle perturbation/mid-level speed maximum within 40-50 kt
west-southwesterly deep layer mean flow.

Given the strength of the deep-layer shear, isolated supercell
structures could evolve within occasionally intensifying stronger
convection through the mid to late afternoon.  It appears that this
could be accompanied by a risk for marginally severe hail, and
melting hail/evaporative cooling in downdrafts may contribute to
downward mixing of higher momentum to the surface.  With
southwesterly flow around 850 mb a somewhat modest 30-40 kt, and
low-level lapse rates relatively weak, peak surface gusts may mostly
remain below severe limits.

..Kerr.. 03/11/2021

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

ATTN...WFO...LMK...PAH...LSX...SGF...

LAT...LON   37749112 38068996 38218908 38358820 38308685 37678695
            37278748 37038972 36699107 37029173 37749112

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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.