MESO: Mesoscale Discussion 1121

ACUS11 KWNS 181956
SWOMCD
SPC MCD 181955
MTZ000-182200-

MESOSCALE DISCUSSION 1121
NWS STORM PREDICTION CENTER NORMAN OK
0255 PM CDT TUE JUN 18 2013

AREAS AFFECTED...WRN MT

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 181955Z - 182200Z

PROBABILITY OF WATCH ISSUANCE...60 PERCENT

SUMMARY...SCATTERED THUNDERSTORM DEVELOPMENT IS UNDERWAY. A GRADUAL
INTENSIFICATION IS EXPECTED LATE THIS AFTERNOON...AND SEVERE WEATHER
POTENTIAL MAY BECOME SUFFICIENT TO REQUIRE A WW...PERHAPS WITHIN THE
NEXT 1-2 HOURS.

DISCUSSION...AHEAD OF A BROAD...ELONGATING MID-LEVEL CLOSED LOW AND
TROUGH GRADUALLY TURNING INLAND ACROSS THE PACIFIC COAST...WEAK
MID-LEVEL HEIGHT FALLS ARE ONGOING ACROSS THE NORTHERN ROCKIES
REGION...BENEATH DIFLUENT HIGH-LEVEL FLOW. IN THE PRESENCE OF THIS
REGIME...DESTABILIZATION ASSOCIATED WITH DAYTIME HEATING...COUPLED
WITH OROGRAPHIC FORCING FOR UPWARD VERTICAL MOTION...ARE
CONTRIBUTING TO INCREASING CONVECTIVE DEVELOPMENT ACROSS THE
BITTERROOT MOUNTAINS AND ADJACENT RANGES OF WESTERN MONTANA.
MID-LEVEL LAPSE RATES ACROSS THIS REGION ARE RATHER
STEEP...SUPPORTING WEAK TO MODERATE CAPE...AND INHIBITION FOR A
RELATIVELY MOIST BOUNDARY LAYER CONTINUES TO SLOWLY WEAKEN AWAY FROM
THE HIGHER TERRAIN. AS A 50+ KT SOUTHERLY 500 MB JET CONTINUES
DEVELOP NORTHWARD THROUGH THE NORTHERN INTERMOUNTAIN
REGION...VERTICAL SHEAR AND THERMODYNAMIC PROFILES WILL BECOME
INCREASINGLY CONDUCIVE TO SUPERCELLS THROUGH THE 21-00Z TIME FRAME.
STRONGEST CELLS LIKELY WILL BECOME CAPABLE OF PRODUCING LARGE HAIL
AND LOCALLY DAMAGING WIND GUSTS.

..KERR/THOMPSON.. 06/18/2013

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

ATTN...WFO...TFX...MSO...

LAT...LON 47631482 48611451 48971215 48541132 46991108 45421184
44801285 45751368 47631482

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