Severe Storm Outlook Narrative (AC)
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571
ACUS11 KWNS 212302
SWOMCD
SPC MCD 212301
WIZ000-IAZ000-MNZ000-220130-

MESOSCALE DISCUSSION 1728
NWS STORM PREDICTION CENTER NORMAN OK
0601 PM CDT WED SEP 21 2016

AREAS AFFECTED...SRN MN...WRN WI AND NRN IA

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 212301Z - 220130Z

PROBABILITY OF WATCH ISSUANCE...60 PERCENT

SUMMARY...A THREAT FOR LARGE HAIL AND WIND DAMAGE MAY INCREASE
ACROSS SRN MN...WRN WI AND NRN IA OVER THE NEXT FEW HOURS. WW
ISSUANCE MAY BECOME NECESSARY AS CELLS INCREASE IN COVERAGE ALONG A
QUASI-STATIONARY FRONT EXTENDING ESEWD ACROSS SRN MN INTO NE IA.

DISCUSSION...LATEST SFC ANALYSIS SHOWS A 1009 MB MESOLOW OVER SE SD
WITH A SLOW MOVING FRONTAL BOUNDARY EXTENDING EWD FROM THE SFC LOW
INTO SRN MN AND SEWD INTO NERN IA. SFC DEWPOINTS ALONG THE BOUNDARY
ARE IN THE MID TO UPPER 60S F WHICH IS CONTRIBUTING TO A MODERATELY
UNSTABLE AIRMASS. MLCAPE VALUES ARE ESTIMATED TO BE IN THE 2000 TO
3000 J/KG RANGE IN SRN MN AND NRN IA ACCORDING TO RAP MESOSCALE
ANALYSIS DATA. A CLUSTER OF SFC-BASED THUNDERSTORMS HAVE DEVELOPED
ALONG THE BOUNDARY FROM FREEBORN COUNTY MN SEWD INTO FLOYD COUNTY IA
WITH THE SERN TWO STORMS SUPERCELLULAR. THESE CELLS ARE BEING
SUPPORTED BY STRONG DIRECTIONAL VEERING OF THE WINDS WITH HEIGHT IN
THE LOWEST 1 KM AGL WITH 30 TO 35 KT OF WSWLY FLOW IN THE
MID-LEVELS. THIS ACTIVITY SHOULD CONTINUE TO POSE A SEVERE WEATHER
THREAT...MOVING EWD TOWARD THE IA-MN-WI INTERSECTION OVER THE NEXT
COUPLE OF HOURS. THE MORE DOMINANT CELLS WITHIN THIS CLUSTER SHOULD
BE ACCOMPANIED BY LARGE HAIL AND ISOLATED WIND DAMAGE WITH A BRIEF
TORNADO ALSO POSSIBLE.

OTHER SFC-BASED THUNDERSTORMS ARE EXPECTED TO DEVELOP THIS EVENING
ACROSS SWRN MN AND POSSIBLY IN NW IA AHEAD OF AN APPROACHING
SHORTWAVE TROUGH. THE LATEST HRRR RUN GRADUALLY ORGANIZES THIS
CONVECTION INTO A EAST TO WEST ORIENTED CONVECTIVE LINE ALONG THE
SRN ROW OF COUNTIES IN MN. IF THIS OCCURS...THEN A POTENTIAL FOR
WIND DAMAGE AND ISOLATED LARGE HAIL MAY PERSIST INTO THE LATE
EVENING AS THIS LINE MOVES SLOWLY SEWD INTO NRN IA. FURTHER
NORTHEAST ACROSS SCNTRL MN AND WCNTRL WI...STORMS WILL REMAIN
ELEVATED AND COULD POSE A HAIL THREAT THIS EVENING.

..BROYLES/GRAMS.. 09/21/2016

...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...

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

LAT...LON   44309612 44879578 45149454 45169287 44969154 44589052
            43949021 42919036 42519099 42779309 43379508 43849595
            44309612




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