Mesoscale Discussion 619

Issued

May 15, 2021, 1:16 PM CDT (18:16 UTC)

Expired

May 15, 2021, 3:15 PM CDT

In force

119 min

Issued by

the Storm Prediction Center

Concerning

Severe potential...watch unlikely

Chance of a watch

20%

The Des Moines radar (KDMX), 147 km from the middle of the area, began a volume at 18:17 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.

269 
ACUS11 KWNS 151817
SWOMCD
SPC MCD 151816 
MNZ000-WIZ000-IAZ000-152015-

Mesoscale Discussion 0619
NWS Storm Prediction Center Norman OK
0116 PM CDT Sat May 15 2021

Areas affected...Central Iowa into portions of Minnesota and
Wisconsin

Concerning...Severe potential...Watch unlikely 

Valid 151816Z - 152015Z

Probability of Watch Issuance...20 percent

SUMMARY...Isolated thunderstorms are expected to develop along a
wind shift boundary within the next 1 to 2 hours and pose a low-end
risk for severe hail/gusty winds. Low coverage and uncertainty in
the severity of the expected storms suggests a weather watch is
unlikely.

DISCUSSION...As of 1730 UTC, visible satellite data showed a
deepening cumulus field with several taller towers ahead of a
shortwave trough across north-central Iowa and southern Minnesota.
Surface observations indicate the presence of a wind-shift boundary
aiding in localized low-level convergence near the Iowa-Minnesota
border. With additional heating and weak background lift from the
slow moving trough expected in the next few hours over the already
warm and modestly moist airmass, (temps in the 70s F with dewpoints
near 50 F), isolated thunderstorm development appears likely. While
upper-level flow will not be overly strong, SPC mesoanalysis shows
between 30 and 40 kts of effective shear will be colocated with
250-500 J/kg of MLCAPE. A few multi-cell storms or weak supercells
will be capable of producing marginally severe hail or gusty outflow
winds this afternoon. 

Downstream across portions of eastern Iowa and Wisconsin, widespread
cloud cover and precipitation have resulted in a cool and stable
boundary layer. Thus, a relatively narrow corridor of
destabilization exists, suggesting the greatest threat for any
severe weather will be confined to portions of north-central Iowa
and southeastern Minnesota this afternoon before storms encounter a
much more hostile environment early this evening. Given the limited
spatial and temporal threat, a weather watch is unlikely.

..Lyons/Guyer.. 05/15/2021

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

ATTN...WFO...DVN...ARX...MPX...DMX...FSD...OAX...

LAT...LON   41229492 41609547 41999560 42649555 43219530 43789445
            44559388 45319360 45709300 45289234 44659209 43339194
            42519196 41969245 41569333 41349391 41229492

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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.