Severe Storm Outlook Narrative (AC)
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000
ACUS11 KWNS 210101
SWOMCD
SPC MCD 210101
WIZ000-IAZ000-MNZ000-210300-

MESOSCALE DISCUSSION 1723
NWS STORM PREDICTION CENTER NORMAN OK
0801 PM CDT TUE SEP 20 2016

AREAS AFFECTED...SRN MN...NERN IA THROUGH WRN WI

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 210101Z - 210300Z

PROBABILITY OF WATCH ISSUANCE...60 PERCENT

SUMMARY...THUNDERSTORMS ARE EXPECTED TO INCREASE IN COVERAGE FROM
SRN MN THROUGH WRN WI THIS EVENING. INITIAL THREAT WILL LIKELY BE
LARGE HAIL...POSSIBLY TRANSITIONING TO DAMAGING WIND. TRENDS ARE
BEING MONITORED FOR A POSSIBLE WW.

DISCUSSION...THIS EVENING A WARM FRONT EXTENDS FROM A SFC LOW IN
SERN SD...SEWD THROUGH SWRN MN AND CNTRL IA. A RESERVOIR OF STRONG
INSTABILITY /3000-4000 J/KG MLCAPE/ RESIDES SOUTH OF THIS
BOUNDARY...BUT A WARM EML WITH STEEP MID-LEVEL LAPSE RATES HAS
OVERSPREAD THE WARM SECTOR CONTRIBUTING TO A CAPPING INVERSION.
MID-LEVEL FORCING FOR ASCENT ASSOCIATED WITH A WEAK LOW-AMPLITUDE
IMPULSE HAS RESULTED IN ELEVATED STORMS FROM WRN THROUGH NRN WI.
THESE STORMS ARE BASED NEAR 700 MB AND WILL POSE LIMITED SEVERE
POTENTIAL...BUT SMALL HAIL CANNOT BE RULED OUT.

A MORE SUBSTANTIAL SEVERE THREAT IS EXPECTED FARTHER WEST ACROSS SRN
MN THIS EVENING WHERE THETA-E ADVECTION ASSOCIATED WITH THE SWLY LLJ
WILL CONTINUE TO DESTABILIZE THE ATMOSPHERE ABOVE THE STABLE SFC
LAYER. OBJECTIVE ANALYSIS ALREADY SHOWS 1500-2500 J/KG MUCAPE FROM
SCNTRL THROUGH SWRN MN. ISENTROPIC ASCENT AND MOIST ADVECTION
RESULTING FROM THE LLJ INTERACTING WITH THE WARM FRONT SHOULD
EVENTUALLY CONTRIBUTE TO DEVELOPMENT OF ELEVATED STORMS OVER SCNTRL
MN. EFFECTIVE SHEAR FROM 35-45 KT THROUGH THE CLOUD LAYER...STEEP
MID LEVEL LAPSE RATES AND MODERATE INSTABILITY WILL PROMOTE A THREAT
OF LARGE HAIL. STORMS MAY EVENTUALLY EVOLVE INTO AN MCS...AND IF
THESE STORMS CAN BECOME FORWARD PROPAGATING...THE THREAT FOR
DAMAGING WIND WOULD INCREASE FROM SERN MN...NERN IA INTO SWRN WI.

..DIAL/HART.. 09/21/2016

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

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

LAT...LON   44929468 44899107 43659003 42979097 43169260 43799509
            44319575 44929468



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