MESO: Mesoscale Discussion 0635

ACUS11 KWNS 131907
SWOMCD
SPC MCD 131907
MTZ000-IDZ000-ORZ000-WAZ000-132130-

MESOSCALE DISCUSSION 0635
NWS STORM PREDICTION CENTER NORMAN OK
0207 PM CDT MON MAY 13 2013

AREAS AFFECTED...NERN ORE...SERN WA...CNTRL ID...PORTIONS OF
WRN/CNTRL MT

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 131907Z - 132130Z

PROBABILITY OF WATCH ISSUANCE...60 PERCENT

SUMMARY...A SEVERE THUNDERSTORM WATCH MAY BE NEEDED DURING THE NEXT
COUPLE OF HOURS...AS THE RISK FOR DMGG WIND GUSTS AND SVR HAIL
INCREASES.

DISCUSSION...DIURNALLY DEEPENING PBL CIRCULATIONS INTO A MID-LEVEL
MOIST PLUME THAT ANTICYCLONICALLY ARCS AROUND THE CREST OF A
NRN-GREAT-BASIN/NRN-ROCKIES RIDGE IS ALLOWING SFC DEWPOINTS TO HOLD
IN THE 40S TO LOWER 50S ACROSS MUCH OF THE AREA...AMIDST PW VALUES
OF 0.65-0.80 INCH PER GPS DATA. STRONG DIURNAL HEATING WILL YIELD
SBCAPE VALUES OF 500-1000 J/KG THROUGH THE AFTERNOON WITHIN A ZONE
OF 6-7-C/KM 700-500-MB LAPSE RATES OVER THE NRN PERIPHERY OF THE
RIDGE. STRENGTHENING OROGRAPHIC CIRCULATIONS WILL ALLOW CONVECTION
TO DEEPEN DURING THE NEXT COUPLE OF HOURS...WITH ZONES OF
PREFERENTIAL DEVELOPMENT OVER
/1/ MOUNTAINS OF NERN ORE INTO SERN WA AND CNTRL ID IN CLOSER
PROXIMITY TO AN APPROACHING MID-LEVEL SHORTWAVE IMPULSE AND LEADING
ZONE OF STRONG MID-LEVEL FORCING FOR ASCENT/HEIGHT FALLS/SFC
FRONT...AND
/2/ MORE ISOLATED MOUNTAINS IN CNTRL MT NEAR AND S OF GTF WHERE
AREAS OF UPSLOPE FLOW EXIST PER TFX VWP DATA AND LOW-LEVEL LAPSE
RATES WILL APPROACH DRY ADIABATIC.

ONCE STORMS DEVELOP -- MOST LIKELY IN THE 20-22Z TIME FRAME -- THEY
WILL QUICKLY MOVE ENEWD/EWD OWING TO STRENGTHENING MID-LEVEL FLOW
DOWNSTREAM OF THE SHORTWAVE IMPULSE. VWP DATA UPSTREAM ALREADY
INDICATE WSWLY FLOW HAVING INCREASED TO AOA 50 KT ABOVE 4 KM AGL PER
UPSTREAM OBS ACROSS WA. THIS WILL ALSO CONTRIBUTE TO STRONG DEEP
SHEAR...SUPPORTING HIGH-BASED SUPERCELLS WITH SVR HAIL AND DMGG
WINDS. ONE OR TWO CONVECTIVE CLUSTERS COULD EVOLVE OVER THE HIGH
PLAINS OF CNTRL MT DURING THE LATE AFTERNOON AND EVENING HOURS AS
DEEP MIXED LAYERS ENHANCE STRONG SUB-CLOUD EVAPORATION...POTENTIALLY
SUPPORTING MERGING COLD POOLS. DMGG WIND GUSTS WOULD BECOME
INCREASINGLY LIKELY WITH ANY MORE ORGANIZED BOWING SEGMENTS.

..COHEN/WEISS.. 05/13/2013

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

ATTN...WFO...BYZ...GGW...TFX...MSO...BOI...OTX...PDT...

LAT...LON 43981856 43961961 44801992 45561926 46621704 48051255
48640881 48150715 47020704 46560882 45781282 45311455
44301734 43981856

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