MESO: Mesoscale Discussion 1253

ACUS11 KWNS 201741
SWOMCD
SPC MCD 201740
UTZ000-NVZ000-201915-

MESOSCALE DISCUSSION 1253
NWS STORM PREDICTION CENTER NORMAN OK
1240 PM CDT SAT JUN 20 2009

AREAS AFFECTED...SRN/ERN NV AND WRN UT

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 201740Z - 201915Z

STRONG THUNDERSTORM WIND GUSTS AND LARGE HAIL ARE POSSIBLE OVER
SRN/ERN NV INTO WRN UT DURING THE REMAINDER OF THIS MORNING AND INTO
THE AFTERNOON. THE AREA IS BEING MONITORED FOR A WW.

12Z UPPER AIR ANALYSIS AND RECENT WV IMAGERY DEPICT A COMPACT BUT
RATHER POTENT S/W TROUGH MOVING E INTO THE GREAT BASIN. STRONG UVV/S
OCCURRING AHEAD OF THIS FEATURE ARE FOCUSING A CONCENTRATED AREA OF
THUNDERSTORM DEVELOPMENT OVER SRN/ERN NV. A COLD MID LEVEL AIRMASS
/AOB -12 DEG C/ IS ALSO ADVANCING E WITH THE UPPER TROUGH...AND IS
AIDING IN STEEPENING LOW TO MID LEVEL LAPSE RATES. SURFACE
TEMPERATURES SOUTH AND EAST OF A BAND OF CLOUDINESS POSITIONED OVER
CENTRAL INTO ERN/NERN NV ARE EXPECTED TO CONTINUE WARMING INTO THE
70S AND 80S. THIS HEATING COMBINED WITH MODEST SURFACE DEWPOINTS
/MAINLY IN THE LOW TO MID 40S/ RESIDING ALONG AND TO THE COOL SIDE
OF A COLD FRONT POSITIONED FROM NEAR SLC TO JUST N OF LAS...WILL AID
IN THE DEVELOPMENT OF 1000 J/KG MLCAPE. THE COMBINATION OF FAVORABLE
LARGE SCALE ASCENT...FRONTAL FORCING...AND INCREASING POTENTIAL
INSTABILITY SHOULD MAINTAIN CURRENT STORMS OVER SRN NV...WITH A
POSSIBLE EXPANSION IN COVERAGE NEWD INTO UT.

RUC FORECAST GUIDANCE AND VWP DATA INDICATE A BAND OF 40 KT MID
LEVEL FLOW POSITIONED ALONG THE SRN AND ERN FRINGE OF THE MID/UPPER
LEVEL TROUGH. THIS FLOW WILL FAVOR SUFFICIENT VERTICAL WIND SHEAR
FOR ORGANIZED THUNDERSTORM DEVELOPMENT...INCLUDING SUPERCELLS.
RELATIVELY COLD MID LEVEL TEMPERATURES AND STEEP LAPSE RATES MAY
YIELD STORMS POSING A LARGE HAIL THREAT...WHILE STEEPENING LOW LEVEL
LAPSE RATES AND MODERATELY STRONG FLOW ALOFT COULD ALSO RESULT IN A
DAMAGING WIND THREAT.

..GARNER.. 06/20/2009

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

ATTN...WFO...SLC...VEF...LKN...

LAT...LON 36441621 36881680 38221662 40491425 40861301 40371250
39451238 38381302 37061430 36391549 36441621

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