Mesoscale Discussion 1032

Issued

Jun 20, 2021, 10:57 AM CDT (15:57 UTC)

Expired

Jun 20, 2021, 1:00 PM CDT

In force

2 hr

Issued by

the Storm Prediction Center

Concerning

Severe potential...watch likely

Chance of a watch

80%

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231 
ACUS11 KWNS 201558
SWOMCD
SPC MCD 201557 
INZ000-ILZ000-IAZ000-MOZ000-201800-

Mesoscale Discussion 1032
NWS Storm Prediction Center Norman OK
1057 AM CDT Sun Jun 20 2021

Areas affected...far southeast IA...far northeast MO...much of
central into northern IL...northwest IN

Concerning...Severe potential...Watch likely 

Valid 201557Z - 201800Z

Probability of Watch Issuance...80 percent

SUMMARY...A watch will likely be needed for parts the mid MS Valley
across IL and into northwest IN.  Storms are expected to develop,
intensify, and pose a severe risk as they move from near the
IL/IA/MO border east-northeast across IL to the southern shore of
Lake MI during the afternoon and early evening.  Convective trends
will be monitored through the late morning and into the midday hours
for an eventual likely watch issuance.

DISCUSSION...Radar mosaic late this morning shows a series of MCVs
located from northeast IA, central IA, and northern MO moving east. 
Visible satellite shows a growing thunderstorm cluster across
northern MO associated with the southern-most MCV.  Surface analysis
places an outflow boundary from northeast MO east into central IL. 
South of the boundary, southerly surface winds and temperatures in
the lower 80s with dewpoints near 70 deg F are noted as of 10am
observations.  North of the boundary, cloud debris has tempered
surface heating with temperatures ranging from the mid 70s from a
Quincy to Peoria line and lower 70s over northern IL.

Model guidance varies considerably regarding the details of
potential convective evolution across central and northern IL this
afternoon.  As a result, there is relatively large uncertainty. 
However, timing of the MCV and its eastward translation would lead
to the potential for storm development and a corresponding risk for
severe as it progresses east across the middle MS Valley.  Forecast
sounding show moderate destabilization across central IL by early to
mid afternoon (2000-2500 J/kg MLCAPE).  Equally important, the low
to mid-level flow fields strengthen and forecast hodographs enlarge
during the mid to late afternoon.  Consequently, it seems the risk
for organized severe storms (including bows or supercells or mix
thereof) and the associated severe hazards will increase coincident
with this wind field response.  Due to the large spread in possible
solutions for this forecast, observational trends will
disproportionately weigh in the decision of a potential severe-storm
watch issuance.

..Smith/Hart.. 06/20/2021

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

ATTN...WFO...IND...LOT...ILX...LSX...DVN...

LAT...LON   39309102 39829185 40579196 41649092 42008766 41378701
            40188735 39309102

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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.