Mesoscale Discussion 1487

Issued

Aug 11, 2021, 3:56 PM CDT (20:56 UTC)

Expired

Aug 11, 2021, 6:30 PM CDT

In force

3 hr

Issued by

the Storm Prediction Center

Concerning

Severe potential...watch possible

Chance of a watch

40%

The Quad Cities radar (KDVN), 74 km from the middle of the area, began a volume at 20:59 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.

620 
ACUS11 KWNS 112056
SWOMCD
SPC MCD 112056 
ILZ000-IAZ000-MOZ000-112330-

Mesoscale Discussion 1487
NWS Storm Prediction Center Norman OK
0356 PM CDT Wed Aug 11 2021

Areas affected...Portions of eastern IA...far northeastern MO...and
northwestern IL

Concerning...Severe potential...Watch possible 

Valid 112056Z - 112330Z

Probability of Watch Issuance...40 percent

SUMMARY...If storms develop and can be sustained, then the threat
for large hail and damaging winds would increase. Convective trends
will be closely monitored, with watch issuance possible.

DISCUSSION...Recent attempts at convective initiation have been
noted across eastern IA along/east of a surface cold front. This
region is on the southern extent of an upper trough over central
Canada and the Upper Midwest, with minimal mid-level height falls
noted. Still, latest mesoanalysis suggests that airmass just ahead
of the front is extremely unstable and uncapped, with MLCAPE of
3500-4500 J/kg present. Latest VWP from KDVN shows winds veering
with height through mid levels and strengthening to around 45-50 kt
above 3 km. Related 35-40 kt of deep-layer shear would be supportive
of supercells. The presence of steep mid-level lapse rates and a
very favorable thermodynamic environment suggests a threat for large
hail with any supercell that can form and be sustained. Damaging
downdraft winds would also be a concern. The main question is
whether any robust storms will be able to form given the weak
large-scale ascent aloft. This region will be closely monitored for
signs of increasing convective coverage/intensity, with watch
issuance possible.

..Gleason/Thompson.. 08/11/2021

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

ATTN...WFO...ILX...LSX...DVN...DMX...EAX...

LAT...LON   42569181 42569103 42318996 41858989 41039014 40339104
            40209211 40259298 41129292 42139242 42569181

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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.