DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 180050
SWODY1
SPC AC 180047

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0747 PM CDT TUE SEP 17 2013

VALID 180100Z - 181200Z

...THERE IS A SLGT RISK OF SVR TSTMS FOR SWRN MT...SERN ID...WRN
WY...NERN UT...AND NWRN CO...

...NERN UT...NWRN CO...SERN ID...SWRN MT AND WRN WY...
SCATTERED TO NUMEROUS THUNDERSTORMS ARE ONGOING THIS EVENING FROM
SRN MT SWD INTO THE FOUR CORNERS REGION. THOUGH MOISTURE IS SOMEWHAT
MARGINAL /PW VALUES FROM 0.75-0.9 INCH/...A STEEP LAPSE RATE
ENVIRONMENT COMBINED WITH EFFECTIVE BULK SHEAR FROM 40-50 KT HAS
SUPPORTED MULTICELL LINE SEGMENTS AND A FEW SUPERCELLS PRODUCING
DAMAGING WINDS...LARGE HAIL...AND EVEN A COUPLE OF TORNADOES. LOSS
OF DAYTIME HEATING AND A STABILIZING BOUNDARY LAYER WILL EVENTUALLY
LEAD TO AN ENVIRONMENT THAT WILL BE INCREASINGLY MARGINAL FOR
SURFACE BASED THUNDERSTORMS AND SEVERE WEATHER ACROSS THE SLGT RISK
AREA. REFER TO WW 526 AND ASSOCIATED MCD/S FOR ADDITIONAL SHORT-TERM
DETAILS ON THE SEVERE WEATHER THREAT.

FARTHER N...LARGE-SCALE ASCENT OCCURRING WITHIN THE EXIT REGION OF
AN 80+ KT UPPER JET STREAK WILL BE FOCUSED OVER MT...WHICH WILL
CONTINUE TO SUPPORT THUNDERSTORM DEVELOPMENT AFTER DARK.
HOWEVER...BOUNDARY LAYER DESTABILIZATION WAS WEAK DURING THE
AFTERNOON...AND IS NOT FORECAST TO IMPROVE OVERNIGHT. THUS...THE
SEVERE WEATHER THREAT WILL BE RATHER MARGINAL OVER THE NRN
ROCKIES/NRN HIGH PLAINS DESPITE FAVORABLE ASCENT AND SHEAR.

...ERN MT...WRN ND...
SURFACE BAROCLINIC ZONE EXTENDED SWWD FROM SERN SASKATCHEWAN INTO
ERN MT THIS EVENING...AND WILL SERVE TO FOCUS SURFACE CYCLOGENESIS
LATER TONIGHT AND SUBSEQUENT INCREASE IN LOW-LEVEL SELYS. STRONG
BOUNDARY LAYER DESTABILIZATION CHARACTERIZED BY TEMPERATURES IN THE
80S AND STEEP LOW-LEVEL LAPSE RATES ARE OBSERVED ALONG THE BOUNDARY
THIS EVENING...AND HAVE BECOME COLLOCATED WITH DEWPOINTS IN THE 50S.
THIS LOW-LEVEL THERMODYNAMIC ENVIRONMENT COMBINED WITH STEEP
MIDLEVEL LAPSE RATES IS AIDING IN MLCAPE VALUES NEAR 500 J/KG /AS
SUGGESTED BY MODIFIED 00Z RAOB FROM RAP/...THOUGH CAPE VALUES WILL
DROP AS THE SURFACE COOLS TONIGHT. ISOLATED THUNDERSTORMS HAVE
DEVELOPED OVER WRN ND AND SERN MT AS A RESULT...WITH ANOTHER WEAKER
AREA OF SHOWERS AND STORMS APPROACHING THE AREA FROM THE W. A FEW
CELLS COULD BRIEFLY BECOME SEVERE GIVEN THE PRESENCE OF STEEP
MIDLEVEL LAPSE RATES AND EFFECTIVE BULK SHEAR UP TO 30 KT.
HOWEVER...INCREASINGLY MARGINAL BUOYANCY IS EXPECTED TO PRECLUDE AN
ORGANIZED SEVERE WEATHER THREAT. REFER TO MCD 1890 FOR ADDITIONAL
SHORT-TERM DETAILS.

..GARNER.. 09/18/2013

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