Severe Storm Outlook Narrative (AC)
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000
ACUS11 KWNS 210634
SWOMCD
SPC MCD 210633
WIZ000-IAZ000-MNZ000-210830-

MESOSCALE DISCUSSION 1725
NWS STORM PREDICTION CENTER NORMAN OK
0133 AM CDT WED SEP 21 2016

AREAS AFFECTED...SERN MINNESOTA...NERN IOWA PARTS OF SWRN AND
CENTRAL WISCONSIN

CONCERNING...SEVERE THUNDERSTORM WATCH 486...

VALID 210633Z - 210830Z

THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH 486
CONTINUES.

SUMMARY...A MOSTLY MARGINAL SEVERE HAIL/WIND THREAT MAY CONTINUE
WITH STRONGER STORMS ACROSS SOUTHEASTERN MINNESOTA/SOUTHWESTERN
WISCONSIN...GENERALLY WEST OF LA CROSS THROUGH THE LA CROSSE
AREA...FOR ANOTHER COUPLE OF HOURS.  IT APPEARS UNLIKELY THAT A NEW
WATCH WILL BE NEEDED...BUT IT IS POSSIBLE THAT PORTIONS OF WATCH 486
COULD BE LOCALLY EXTENDED IN TIME/AREA.

DISCUSSION...A WEAK MID-LEVEL WAVE ON THE SOUTHERN FRINGE OF THE
STRONGER MID-LATITUDE WESTERLIES IS NOW CROSSING THE UPPER
MIDWEST...AND LIKELY WILL CONTINUE EASTWARD TOWARD THE GREAT LAKES
REGION THROUGH DAYBREAK.  AS THIS OCCURS...THE LATEST RAPID REFRESH
SUGGESTS THAT A BRANCH OF STRONGER WEST SOUTHWESTERLY 850 MB FLOW
EMANATING FROM THE MID MISSOURI VALLEY WILL GRADUALLY WEAKEN /FROM
CURRENT 35-40 KT/ ACROSS SOUTHEASTERN MINNESOTA/ADJACENT
NORTHEASTERN IOWA INTO SOUTHERN WISCONSIN.  DIMINISHING INFLOW OF
AIR CHARACTERIZED BY MODERATE CAPE SEEMS LIKELY TO LEAD TO WEAKENING
CONVECTIVE INTENSITY.

UNTIL THIS OCCURS...THE RISK FOR SEVERE HAIL MAY CONTINUE ANOTHER
COUPLE OF HOURS...MAINLY WITH CELLS ON THE SOUTHWESTERN FLANK OF THE
EVOLVING CLUSTER OF STORMS...IN CLOSEST PROXIMITY TO THE SURFACE
WARM FRONTAL ZONE.  EVEN THOUGH ACTIVITY IS GENERALLY ROOTED ABOVE A
STABLE SURFACE-BASED LAYER...THIS LAYER APPEARS SHALLOW
ENOUGH...COUPLED WITH AN INITIALLY DRY SUB-CLOUD LAYER... TO ALLOW
FOR DOWNWARD MOMENTUM TRANSFER TO CONTRIBUTE TO SURFACE GUSTS
OCCASIONALLY APPROACHING SEVERE LIMITS.  THIS THREAT APPEARS
GREATEST NEAR THE CORE OF THE STRONGER 850 MB FLOW EXPECTED TO
PROPAGATE ACROSS THE LA CROSSE AREA DURING THE NEXT COUPLE OF HOURS.

..KERR.. 09/21/2016

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

ATTN...WFO...GRB...MKX...ARX...MPX...

LAT...LON   44429464 45099252 44839046 44138928 43468859 42868956
            43139103 43299228 43949431 44429464




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