Severe Storm Outlook Narrative (AC)
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000
ACUS11 KWNS 190200
SWOMCD
SPC MCD 190200
IAZ000-MNZ000-190300-

Mesoscale Discussion 1528
NWS Storm Prediction Center Norman OK
0900 PM CDT Fri Aug 18 2017

Areas affected...Portions of far south-central MN and
northern/central IA

Concerning...Severe Thunderstorm Watch 456...

Valid 190200Z - 190300Z

The severe weather threat for Severe Thunderstorm Watch 456
continues.

SUMMARY...Isolated severe threat in the short term appears greatest
across western portions of WW 456 with an ongoing supercell
thunderstorm.

DISCUSSION...A cluster of storms across southern MN with an embedded
MCV has evolved over the past several hours into a dominant
supercell on the southwestern flank of a short line of storms
extending across far northern IA into far south-central MN. This
supercell has produced hail up to 2 inches in diameter and likely a
tornado earlier in Osceola County IA. Temperatures have quickly
cooled across the eastern portions of WW 456 with the loss of
daytime heating, and a pronounced instability gradient is present
across IA as of 0145Z. The primary severe threat over the next hour
or two should remain focused across the western tier or two of
counties in WW 456 in association with the southeastward-moving
supercell. Isolated large hail and damaging winds will be possible
given the combination of sufficient instability and effective bulk
shear of 35-45 kt supporting updraft organization. The tornado
threat with this supercell should decrease later this evening as
convective inhibition continues to increase.

..Gleason.. 08/19/2017

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

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

LAT...LON   43109580 43899454 43849311 42889307 42289256 41239261
            41219462 42229505 43109580
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