Mesoscale Discussion 240

Issued

Mar 23, 2021, 7:31 PM CDT (00:31 UTC)

Expired

Mar 23, 2021, 9:00 PM CDT

In force

89 min

Issued by

the Storm Prediction Center

Concerning

Severe potential...watch unlikely

Chance of a watch

5%

Counties Brown County, IL, Calhoun County, IL, Greene County, IL, Jersey County, IL, Pike County, IL, Schuyler County, IL, Scott County, IL

The St Louis radar (KLSX), 115 km from the middle of the area, began a volume at 00:33 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

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076 
ACUS11 KWNS 240031
SWOMCD
SPC MCD 240031 
ILZ000-MOZ000-240200-

Mesoscale Discussion 0240
NWS Storm Prediction Center Norman OK
0731 PM CDT Tue Mar 23 2021

Areas affected...Parts of northwest/west central Illinois into east
central Missouri

Concerning...Severe potential...Watch unlikely 

Valid 240031Z - 240200Z

Probability of Watch Issuance...5 percent

SUMMARY...A couple of low-topped supercells may pose a risk for
small hail, locally strong wind gusts and perhaps some risk for a
brief, weak tornado another hour or two before diminishing fairly
quickly after sunset.

DISCUSSION...There has been a recent increase in low/mid-level
rotation evident in intensifying convective cells to northwest of
St. Louis, MO.  This is generally just to the south of the narrow
squall line supported by an arcing band of stronger mid-level
forcing for ascent associated with the mid-level low progressing
into/across the central Missouri/Iowa border area.

Warming associated with subsidence evident in water vapor imagery to
the south is still suppressing thunderstorm development, but breaks
in cloud cover within the moist warm sector have contributed to a
corridor of weak mixed-layer CAPE up to 250 J/kg.  For surface
parcels CAPE may be has high as 500 J/kg, allowing for a brief flare
up of stronger convection contributing to the increased rotation,
supported by moderately large, clockwise curved low-level hodographs
beneath a 30-40+ kt southerly 850 mb jet.  It is possible that this
could continue across the river into parts of northwest and west
central Illinois, accompanied by a risk for small hail and locally
strong surface gusts, with perhaps some potential for a brief, weak
tornado.  However, this potential is expected to diminish as the
intensity of the convection wanes fairly rapidly after sunset.

..Kerr/Guyer.. 03/24/2021

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

ATTN...WFO...ILX...LSX...DVN...

LAT...LON   39539098 39819104 40189111 40269109 40649094 39919026
            39069028 38659060 39539098

Mesoscale 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.