MESO: Mesoscale Discussion 1221

ACUS11 KWNS 251946
SWOMCD
SPC MCD 251945
SDZ000-NDZ000-252215-

MESOSCALE DISCUSSION 1221
NWS STORM PREDICTION CENTER NORMAN OK
0245 PM CDT TUE JUN 25 2013

AREAS AFFECTED...A LARGE PART OF ND...PORTIONS OF N-CNTRL/NERN SD

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 251945Z - 252215Z

PROBABILITY OF WATCH ISSUANCE...60 PERCENT

SUMMARY...THE SVR POTENTIAL WILL INCREASE ACROSS THE AREA THROUGH
THE AFTERNOON HOURS...AND THE ISSUANCE OF A WW MAY BE NEEDED.

DISCUSSION...HOLES IN FAIRLY WIDESPREAD/OPAQUE MULTI-LAYERED CLOUDS
ACCOMPANYING MID-LEVEL ASCENT PRECEDING A SHORTWAVE TROUGH
APPROACHING THE AREA REVEAL A BOUNDARY-LAYER CUMULUS FIELD BECOMING
INCREASINGLY AGITATED OVER S-CNTRL ND PER VIS SATELLITE IMAGERY.
TRANSIENT RADAR ECHOES HAVE BEEN NOTED PER BIS WSR-88D RADAR DATA
ACROSS S-CNTRL ND AND N-CNTRL SD...REFLECTING AN INCREASE IN
MID-LEVEL CONVECTION...THOUGH SUSTAINED CONVECTIVE GROWTH HAS THUS
FAR BEEN LACKING AS MLCINH REMAINS -- PER MODIFIED 12Z BIS RAOB AND
FORECAST SOUNDINGS. HOWEVER...GIVEN THIS SIGNAL OF INCREASING
MID-LEVEL ASCENT AMIDST A DEEPENING/HEATING BOUNDARY
LAYER...SFC-BASED CONVECTIVE INITIATION MAY OCCUR WITHIN THE
2030-2200Z TIME FRAME. THE MOST LIKELY AREA FOR INITIATION WILL BE
ALONG A N/S-ORIENTED SFC TROUGH/WIND-SHIFT AXIS THAT ARCS FROM NWRN
ND SSEWD INTO CNTRL SD. SFC MESOANALYSIS INDICATES A WEAK WARM FRONT
EXTENDING FROM NERN SD INTO N-CNTRL ND THAT INTERSECTS THE TROUGH
OVER NWRN ND. THIS INTERSECTION POINT MAY ALSO SERVE AS A FOCUS FOR
ENHANCED LOW-LEVEL ASCENT AND CONVECTIVE INITIATION.

WHILE A STRONG EML OVER THE AREA MAY DELAY THE ONSET OF CONVECTION
DURING THE NEXT HOUR OR SO...STEEP MID-LEVEL LAPSE RATES ACCOMPANY
THIS EML AS SAMPLED BY THE 12Z BIS RAOB -- AROUND 8.5 C/KM IN THE
H7-H5 LAYER. RICH LOW-LEVEL MOISTURE WITH SFC DEWPOINTS IN THE UPPER
60S AND LOWER 70S AMIDST AREAS OF SFC DIABATIC HEATING ARE
CONTRIBUTING TO 3000-4500 J/KG OF MLCAPE. EXTREME INSTABILITY IS
CONFINED TO LOCATIONS S OF THE WARM FRONT AND E OF THE SFC TROUGH
FROM CNTRL ND INTO N-CNTRL SD. ONCE STORMS DEVELOP...THIS DEGREE OF
BUOYANCY WILL SUPPORT INTENSE UPDRAFTS/DOWNDRAFTS...WITH SVR
HAIL/WIND LIKELY. ONLY MODEST MID-LEVEL SWLY/S -- I.E. AROUND 20 KT
PER BIS AND MBX VWP DATA -- EXIST...THOUGH THE THERMODYNAMIC
ENVIRONMENT SHOULD OFFSET THE LIMITED DEEP SHEAR IN SUPPORTING SVR
POTENTIAL. VERTICALLY VEERING WIND PROFILES N OF THE WARM FRONT
SHOULD PROVIDE SOME ENHANCEMENT TO LOW-LEVEL SHEAR/STORM
ORGANIZATION. STRONG/MERGING COLD POOLS MAY ALLOW CONVECTION TO GROW
UPSCALE INTO ONE OR MORE FORWARD-PROPAGATING CONVECTIVE CLUSTERS
THROUGH THE LATE AFTERNOON/EVENING...AS MID-LEVEL FLOW WEAKLY
INCREASES IN ASSOCIATION WITH THE SHORTWAVE TROUGH.

THERE IS SOME UNCERTAINTY REGARDING THE TIMING OF THE MOST
SUBSTANTIAL INCREASE IN THE SVR THREAT...AND THE AREA WILL BE
MONITORED FOR INCREASING SVR POTENTIAL AND POTENTIAL WW ISSUANCE
THROUGH THE AFTERNOON.

..COHEN/KERR.. 06/25/2013

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

ATTN...WFO...FGF...FSD...ABR...BIS...

LAT...LON 44930015 45850116 47470231 48300325 48920346 49040235
48569804 44929688 44349847 44930015

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