Mesoscale Discussion 1063

Issued

Jun 22, 2021, 3:41 PM CDT (20:41 UTC)

Expired

Jun 22, 2021, 5:45 PM CDT

In force

2 hr

Issued by

the Storm Prediction Center

Concerning

Severe potential...watch possible

Chance of a watch

40%

The Omaha radar (KOAX), 88 km from the middle of the area, began a volume at 20:42 UTC, the scan nearest the moment this went out.

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• Severe Thunderstorm Watch 305Jun 22, 4:50 PM CDT

234 
ACUS11 KWNS 222042
SWOMCD
SPC MCD 222041 
IAZ000-NEZ000-SDZ000-222245-

Mesoscale Discussion 1063
NWS Storm Prediction Center Norman OK
0341 PM CDT Tue Jun 22 2021

Areas affected...Northeast Nebraska and western Iowa

Concerning...Severe potential...Watch possible 

Valid 222041Z - 222245Z

Probability of Watch Issuance...40 percent

SUMMARY...A couple of strong to severe storms capable of mainly
large hail and damaging winds possible this evening.

DISCUSSION...Mid-level showers and occasional thunderstorms have
been present across western Iowa for much of the day thus far. This
activity is likely a manifestation of the mid-level moisture and
steep lapse rates in a region of isentropic ascent. Therefore,
if/when the MLCIN can erode across this region, surface based storm
development is anticipated. 

A well developed cu field has been advancing eastward across
Nebraska over the last few hours with its eastward extent closely
following the -25 J/kg MLCIN contour from SPC mesoanalysis. Linear
extrapolation and forecast MLCIN from the RAP would suggest this cu
field may advance to near the NE/IA border between 21 and 22Z. This
will be the most likely time for surface based storm development as
a minimally capped low-level environment spreads beneath the plume
of better mid-level moisture and isentropic ascent. The window of
opportunity for storm based storm development is narrow, but the
timing appears favorable and the HRRR also supports the idea of
storms developing around 21Z in the region of Sioux City, IA. 

Any stronger storms which develop will likely be supercellular in
nature given 50 to 55 kts of effective shear per OAX VWP. These
storms will pose a threat for severe hail and damaging winds. Any
storms which develop are only expected to last a few hours before
boundary layer cooling and subsequent increasing inhibition will
likely bring and end to strong storms. While storm intensity is
expected to be sufficient for a severe thunderstorm watch, storm
coverage and longevity may be too limited.

..Bentley/Hart.. 06/22/2021

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

ATTN...WFO...DMX...FSD...OAX...

LAT...LON   41229655 41789765 42329784 42789764 43019625 42429347
            41619263 41059274 40679348 40639438 40599545 41229655

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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.