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ACUS11 KWNS 190741
SWOMCD
SPC MCD 190740
MNZ000-IAZ000-NEZ000-SDZ000-191045-

Mesoscale Discussion 1478
NWS Storm Prediction Center Norman OK
0240 AM CDT Wed Sep 19 2018

Areas affected...Southeast SD...northeast NE...southwest MN...and
northwest IA

Concerning...Severe potential...Watch unlikely

Valid 190740Z - 191045Z

Probability of Watch Issuance...5 percent

SUMMARY...Sustained storms developing across southeast South Dakota
and northeast Nebraska through the early morning will be capable of
producing isolated large hail and perhaps locally strong winds, as
they spread east into northwest Iowa and southwest Minnesota.
Current thinking suggests coverage of the strongest storms should
remain too isolated for watch issuance.

DISCUSSION...A gradual strengthening of west-southwesterly midlevel
winds, associated with a transient impulse moving across SD, will
allow a plume of steep lapse rates to spread east through NE and
southern SD to far western IA overnight, as indicated by trends in
objective analysis and 00Z NAM forecast. Mosaic radar imagery and
MRMS MESH indicated an increase of sustained updraft intensities
since 0610Z, and some periodic greater potential for hail
approaching 1 inch in diameter, with a storm that initially moved
through Keya Paha County, NE and Gregory County, SD. This elevated
storm and other widely scattered elevated showers/storms straddling
the NE/SD border region were located within a broad regime of warm
advection, given a 30-35-kt south-southwesterly low-level jet
extending from west TX into much of NE.

The synoptic boundary remains well south of this thunderstorm
development area. However, the presence of greater low-level
moisture across the central Plains per 00Z upper air analysis at 850
mb and steep midlevel lapse rates are aiding in moderate elevated
MUCAPE. This combined with strong effective bulk shear supports an
environment favorable for elevated rotating updrafts capable of
producing hail. The lack of greater forcing for ascent aloft due to
the low-amplitude of the transient impulse should temper the overall
coverage of this potential severe threat, as storms develop and
spread into northwest IA and southwest MN.

..Peters/Edwards.. 09/19/2018

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

ATTN...WFO...MPX...DMX...FSD...OAX...ABR...LBF...UNR...

LAT...LON 43650011 44119882 44379724 44389551 44089460 43369416
42619400 42099411 41899535 42059669 42419924 42590004
43030028 43650011



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