Mesoscale Discussion 1390

Issued

Jul 29, 2021, 2:19 PM CDT (19:19 UTC)

Expired

Jul 29, 2021, 4:15 PM CDT

In force

116 min

Issued by

the Storm Prediction Center

Concerning

Severe potential...watch possible

Chance of a watch

60%

The Lincoln radar (KILX), 23 km from the middle of the area, began a volume at 19:20 UTC, the scan nearest the moment this went out.

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699 
ACUS11 KWNS 291919
SWOMCD
SPC MCD 291919 
INZ000-ILZ000-MOZ000-IAZ000-292115-

Mesoscale Discussion 1390
NWS Storm Prediction Center Norman OK
0219 PM CDT Thu Jul 29 2021

Areas affected...Parts of southeastern Iowa...northeastern
Missouri...central Illinois and Indiana

Concerning...Severe potential...Watch possible 

Valid 291919Z - 292115Z

Probability of Watch Issuance...60 percent

SUMMARY...Scattered strengthening thunderstorm development through
5-7 PM CDT may gradually pose increasing risk for locally damaging
wind gusts.  The potential for activity to consolidate into a larger
cluster that would require a severe weather watch remains uncertain,
and appears relatively low, but trends are being monitored for this
possibility.

DISCUSSION...Forcing for ascent along a stalled outflow boundary has
remained sufficient to maintain sustained modest thunderstorm
development along a corridor near the Burlington, IA through Peoria,
IL vicinities.  Associated outflow and anvil cloud cover and light
precipitation continue to impact the environment to the southeast of
this activity, but the influence may be waning with a corridor of
recent stronger surface pressure falls evident in observations
across the Springfield and Mattoon, IL vicinities.  Additionally,
scattered new thunderstorm development is underway in closer
proximity to the outflow boundary, near/north of the Interstate 74
corridor, into central Indiana.

The newer thunderstorm development coincides with a corridor
seasonably high precipitable water on the order of 2 inches, in the
presence of modest shear beneath 20-40 kt northwesterly flow around
the 500 mb level.  Gradually, with increasing inflow of a very moist
boundary layer characterized by mid/upper 70s surface dew points,
and large CAPE growing in excess of 3000-4000 J/kg with increasing
insolation, substantive further intensification appears probable
through 22-00Z.  This may include the evolution of isolated
supercells and small organizing clusters, with at least modestly
steep lower/mid tropospheric lapse rates and heavy precipitation
loading contributing to the risk for potentially damaging wind
gusts.

..Kerr/Hart.. 07/29/2021

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

ATTN...WFO...ILN...IND...LOT...ILX...LSX...DVN...DMX...EAX...

LAT...LON   40809250 40869094 40858985 40788911 40548762 39848493
            38838683 39058987 39789180 40809250

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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.