MESO: Mesoscale Discussion 1814

ACUS11 KWNS 311910
SWOMCD
SPC MCD 311910
MNZ000-WIZ000-SDZ000-NDZ000-312115-

MESOSCALE DISCUSSION 1814
NWS STORM PREDICTION CENTER NORMAN OK
0210 PM CDT SAT AUG 31 2013

AREAS AFFECTED...PORTIONS ERN DAKOTAS AND MN.

CONCERNING...SEVERE POTENTIAL...WATCH LIKELY

VALID 311910Z - 312115Z

PROBABILITY OF WATCH ISSUANCE...80 PERCENT

SUMMARY...SVR THREAT IS FCST TO INCREASE THROUGH AFTN...WITH INITIAL
MIXTURE OF CONVECTIVE MODES POSSIBLE...INCLUDING
SUPERCELLS...EVENTUALLY EVOLVING INTO QUASI-LINEAR AND CLUSTERED
SYSTEMS. ALL SVR MODES ARE POSSIBLE DURING FIRST FEW HOURS OF THIS
REGIME...EVOLVING TO WIND-DOMINANT. WW LIKELY WILL BE REQUIRED OVER
THIS AREA DURING NEXT 1-2 HOURS.

DISCUSSION...SFC MESOANALYSIS SHOWED COLD FRONT FROM PEMBINA COUNTY
ND SWWD ACROSS PIR AREA...FCST TO MOVE EWD ACROSS DISCUSSION AREA.
LARGE AREA OF MIDLEVEL CONVECTION AND ASSOCIATED BKN-OVC CLOUD COVER
IS MOVING EWD ACROSS N-CENTRAL/NERN SD...ERN ND AND NWRN MN AT ABOUT
30 KT...SOMEWHAT OUTPACING SFC COLD FRONT. HOWEVER...SOME OF THIS
CLOUD/PRECIP MASS REMAINS BEHIND FRONT...AND BULK OF CLOUD AREA
AHEAD OF FRONT WILL CONTINUE TO INHIBIT BOTH PACE AND MAGNITUDE OF
DIABATIC SFC HEATING IN WARM SECTOR. RELATED WEAKENING OF
PREFRONTAL MLCINH IS GRADUAL...BASED ON MODIFIED RAOBS AND FCST
SOUNDINGS...BUT SHOULD ALLOW RELATIVELY UNIMPEDED/SFC-BASED
EFFECTIVE INFLOW PARCELS BY ABOUT 21Z. AS SUCH...WIDELY SCATTERED
TSTMS ALREADY EVIDENT WITHIN CLOUD/PRECIP PLUME MAY BECOME SFC-BASED
IN SITU. ADDITIONAL DEVELOPMENT ALSO IS POSSIBLE ALONG COLD FRONT
ITSELF...AS WELL AS AREAS OF DIFFERENTIAL HEATING ALONG SRN/ERN RIM
OF CLOUD/PRECIP MASS.

SFC MOIST AXIS...WITH PATCHY CONFIGURATION OF MOSTLY MID-UPPER 60S F
SFC DEW POINTS...WAS DRAWN JUST AHEAD OF FRONT OVER ND AND SWD
ACROSS ERN SD NEAR MHE/YKN AREA...WHERE LOW-70S VALUES WERE
OBSERVED. AXIS SHOULD SHIFT EWD AHEAD OF FRONT AMIDST SSWLY/SWLY
SFC FLOW. RELATIVELY VEERED/5-10 KT SFC WINDS WILL LIMIT LOW-LEVEL
SRH/CONVERGENCE...HOWEVER DEEP SHEAR STILL WILL SUPPORT POTENTIAL
FOR SUPERCELLS AND FOR BOWING OF ANY QUASI-LINEAR MODES. DEEP SHEAR
OVER ERN ND AND NRN MN SHOULD INCREASE WITH APCH OF HEIGHT-GRADIENT
ENHANCEMENTS PRECEDING SK SHORTWAVE TROUGH. THIS SHOULD CONTRIBUTE
TO EFFECTIVE-SHEAR MAGNITUDES INCREASING WITH TIME TO 45-55 KT RANGE
OVER MORE OF ERN ND/NWRN MN AND 35-45 KT ELSEWHERE.

..EDWARDS/GOSS.. 08/31/2013

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

ATTN...WFO...DLH...MPX...FGF...FSD...ABR...BIS...

LAT...LON 44679908 47469755 49009702 48989509 49369510 49379494
49359493 49289479 49169482 48939469 48809470 48729455
48709430 48659424 48639386 48539380 48539351 48619342
48619297 48539266 48419249 48229234 48329229 48349205
48069155 48259088 47439107 46709217 45689289 44249369
43589516 43529658 43639937 44679908

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