Mesoscale Discussion 993

Issued

Jun 12, 2017, 11:28 AM CDT (16:28 UTC)

Expired

Jun 12, 2017, 1:00 PM CDT

In force

92 min

Issued by

the Storm Prediction Center

Chance of a watch

80%

The Minneapolis radar (KMPX), 150 km from the middle of the area, began a volume at 16:28 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

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• Severe Thunderstorm Watch 316Jun 12, 11:50 AM CDT

110 
ACUS11 KWNS 121629
SWOMCD
SPC MCD 121628 
WIZ000-IAZ000-MNZ000-SDZ000-121800-

Mesoscale Discussion 0993
NWS Storm Prediction Center Norman OK
1128 AM CDT Mon Jun 12 2017

Areas affected...Southeast South Dakota...southern
Minnesota...northern Iowa

Concerning...Severe potential...Watch likely 

Valid 121628Z - 121800Z

Probability of Watch Issuance...80 percent

SUMMARY...Thunderstorms are expected to increase in coverage and
intensity through the afternoon hours.  Large hail and potentially
damaging winds will be the primary threats and a watch is possible
by 18z.

DISCUSSION...A cluster of thunderstorms occasionally producing large
hail was located over southeast South Dakota and southwest Minnesota
at 1615z.  The storms have thus far been slightly elevated to the
north of a quasi-stationary frontal boundary that extends from
central Nebraska northeast along the Minnesota/Iowa border and into
central/southern Wisconsin.  Temperatures continue to warm to the
south of the front, and with the nose of a plume of steep mid-level
lapse rates across the area, strong surfaced-based instability will
develop this afternoon.  Visible satellite imagery reveals
increasing cumulus field development along the front as CINH erodes,
and thunderstorms are likely to increase in coverage/intensity over
the next few hours within the discussion area. In the presence of
effective shear generally ranging between 30 and 40 kts, supercells
and clusters of severe storms will be possible with large hail and
damaging winds.  Where cold pools can congeal, a more concentrated
damaging wind threat may develop with east/southeast-moving bowing
segments. Some tornado risk will exist given the favorable low-level
SRH near the boundary with the more discrete storms that develop.

Given the expected increase in storm coverage and severe potential,
a watch is likely prior to 1730z for the eastern two-thirds of the
discussion area.

..Bunting/Hart.. 06/12/2017

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

ATTN...WFO...ARX...MPX...DMX...FSD...

LAT...LON   42839358 42899542 42999646 43229705 43469732 43789714
            44069654 44279458 44309312 44259224 44179152 43959075
            43539044 42989076 42779186 42839358

Mesoscale Discussions in Iowa, 2017Mesoscale Discussions in Minnesota, 2017Mesoscale Discussions in Wisconsin, 2017Every mesoscale discussion in 2017

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.