Mesoscale Discussion 1430

Issued

Aug 7, 2021, 11:03 AM CDT (16:03 UTC)

Expired

Aug 7, 2021, 1:30 PM CDT

In force

2 hr

Issued by

the Storm Prediction Center

Concerning

Severe potential...watch possible

Chance of a watch

40%

The La Crosse radar (KARX), 63 km from the middle of the area, began a volume at 16:02 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.

797 
ACUS11 KWNS 071604
SWOMCD
SPC MCD 071603 
WIZ000-IAZ000-MNZ000-071830-

Mesoscale Discussion 1430
NWS Storm Prediction Center Norman OK
1103 AM CDT Sat Aug 07 2021

Areas affected...Portions of southeastern MN...northeastern IA...and
western WI

Concerning...Severe potential...Watch possible 

Valid 071603Z - 071830Z

Probability of Watch Issuance...40 percent

SUMMARY...A threat for large hail, damaging wind gusts, and perhaps
a few tornadoes may increase through the early afternoon. Watch
issuance is possible.

DISCUSSION...Recent visible satellite and radar imagery clearly
shows a MCV moving quickly eastward across MN and towards
west-central WI late this morning. On the southern flank of this
feature, a 25-35 kt southwesterly low-level jet has encouraged a
recent uptick in convection across southeastern MN and northeastern
IA. It appears that this activity is mainly elevated at the moment,
with a weak front/outflow boundary located over southern MN. Still,
with around 35-40 kt of deep-layer shear present, any elevated
supercells may pose an isolated threat for primarily large hail in
the short term. Storms may eventually transition to surface-based
over the next few hours, particularly along and south of the
convectively reinforced boundary over southern MN.

A rich low-level airmass characterized by at least low 70s surface
dewpoints is present across much of IA into southern MN. Both
diurnal heating of this airmass and the presence of steep mid-level
lapse will likely contribute to around 2000-3000 J/kg of MLCAPE this
afternoon. In addition to the large hail threat with any supercells,
damaging winds may also occur if storms can congeal into one or more
clusters and then move east-southeastward along the surface boundary
into western WI. 25-35 kt of southwesterly winds in the boundary
layer and a veering wind profile with height should support 100-200
m2/s2 of 0-1 km SRH, sufficient for updraft rotation and a threat
for a few tornadoes. This tornado threat will probably be maximized
near the surface boundary across parts of southern MN into far
northeastern IA and southwestern WI. Convective trends will be
closely monitored for possible watch issuance in the next few hours.

..Gleason/Thompson.. 08/07/2021

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

ATTN...WFO...MKX...DVN...ARX...MPX...DMX...

LAT...LON   43548995 42998986 42689018 42539067 42409221 42669321
            42949368 43929391 44389282 44439206 44209109 43548995

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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.