Severe Storm Outlook Narrative (AC)
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000
ACUS11 KWNS 222313
SWOMCD
SPC MCD 222312
WIZ000-IAZ000-MNZ000-230015-

MESOSCALE DISCUSSION 1736
NWS STORM PREDICTION CENTER NORMAN OK
0612 PM CDT SAT AUG 22 2015

AREAS AFFECTED...SERN MN / NERN IA / W-CNTRL AND SWRN WI

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 222312Z - 230015Z

PROBABILITY OF WATCH ISSUANCE...40 PERCENT

SUMMARY...THE THREAT FOR A FEW STRONG TO SEVERE STORMS IS EXPECTED
TO INCREASE FROM WEST TO EAST ACROSS THE DISCUSSION AREA THIS
EVENING.  CONVECTIVE TRENDS ARE BEING MONITORED FOR A POSSIBLE WATCH
TO THE EAST OF TORNADO WATCH 497.

DISCUSSION...INCREASED FORCING FOR ASCENT /DCVA/ RELATED TO THE
VIGOROUS MID-LEVEL TROUGH OVER THE NRN PLAINS IS CONTRIBUTING TO A
GRADUAL INCREASE IN TSTMS AHEAD OF THE SURFACE FRONT WITH THE
LEADING EDGE OF THE MORE RECENT STORMS EXTENDING FROM WASECA COUNTY
IN S-CNTRL MN TO HANCOCK COUNTY IN N-CNTRL IA AS OF 23Z.
EXTRAPOLATION OF CURRENT STORM MOTIONS --235/35 KT-- SUGGESTS THAT
THIS ACTIVITY WILL REACH THE ERN EDGE OF TORNADO WATCH 497 BY ABOUT
00Z.

WHILE VERTICAL SHEAR IS STEADILY STRENGTHENING AHEAD OF THE
SYNOPTIC-SCALE TROUGH /REF. CURRENT MPX VAD/...FORECAST SOUNDINGS
SUGGEST AN INCREASING AMOUNT OF CONVECTIVE INHIBITION FOR
SURFACE-BASED PARCELS OWING TO A GENERALLY DRIER BOUNDARY LAYER WITH
EWD EXTENT.  WHILE SOME INCREASE IN LOW-LEVEL MOISTURE MAY OCCUR
OVER THE NEXT SEVERAL HOURS VIA HORIZONTAL ADVECTION...THIS PROCESS
WILL BE OFFSET BY THE ONSET OF NOCTURNAL COOLING OF THE BOUNDARY
LAYER...YIELDING LITTLE NET CHANGE TO THE AMOUNT OF CONVECTIVE
INHIBITION.

ASSUMING CURRENT CONVECTIVE TRENDS PERSIST...A DOWNSTREAM WATCH IS
NOT ANTICIPATED OWING TO THE THERMODYNAMIC CONCERNS HIGHLIGHTED
ABOVE.  HOWEVER...SHOULD STORMS INTENSIFY...AMPLE VERTICAL SHEAR
EXISTS TO FOSTER SUPERCELL MORPHOLOGIES AND AN ATTENDANT GREATER
SEVERE WEATHER THREAT.  THIS LATTER SCENARIO WOULD NECESSITATE MORE
SERIOUS CONSIDERATION FOR A WATCH.

..MEAD.. 08/22/2015

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

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

LAT...LON   43709296 44019298 44129252 44349227 44499203 44319093
            43969057 43019041 42689075 42539142 42519214 42569258
            42759280 42979290 43709296




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