Sep 18, 2013 0600 UTC Day 1 Convective Outlook

DAY 1 CONVECTIVE OUTLOOK  

   NWS STORM PREDICTION CENTER NORMAN OK
   1245 AM CDT WED SEP 18 2013

   VALID 181200Z - 191200Z

   ...THERE IS A SLGT RISK OF SVR TSTMS FOR THE NRN PLAINS...

   ...SYNOPSIS...
   UPPER AIR ANALYSIS AND WV IMAGERY SHOWED A SHORTWAVE TROUGH LOCATED
   OVER THE PAC NW EARLY THIS MORNING...WITH 70 M MIDLEVEL HEIGHT FALLS
   OCCURRING OVER THE NRN ROCKIES. THIS TROUGH IS FORECAST TO MOVE EWD
   INTO THE NRN HIGH PLAINS BY AFTERNOON...AND THEN BEGIN LIFTING NEWD
   TOWARD THE CANADIAN PRAIRIE PROVINCES DURING THE NIGHT. AS THIS
   TAKES PLACE...40-50 KT MIDLEVEL JET...AND 70+ KT UPPER-LEVEL JET
   WILL SPREAD NEWD FROM THE CNTRL ROCKIES INTO THE NRN PLAINS. AT THE
   SURFACE...LOW PRESSURE IS CURRENTLY BEGINNING TO CONSOLIDATE OVER
   ERN MT/WRN ND...WITH FURTHER DEEPENING EXPECTED TO TAKE PLACE LATER
   TODAY AS THE LOW ADVANCES ENEWD ACROSS ND. A WARM FRONT EXTENDING
   SEWD FROM WRN ND INTO THE CNTRL PLAINS THIS MORNING WILL MOVE EWD
   ACROSS ND WITH THE AREA OF SURFACE LOW PRESSURE. MEANWHILE...AS THE
   UPPER TROUGH CATCHES UP WITH THE LOW-LEVEL CYCLONE...A COLD FRONT
   WILL PROGRESS INTO THE WRN DAKOTAS BY AFTERNOON...AND ENTER WRN MN
   BY THE END OF THE FORECAST PERIOD.

   ...NRN PLAINS...
   MID TO LOCALLY UPPER 60S DEWPOINTS OVER THE CNTRL PLAINS ARE
   FORECAST TO ADVECT NWD INTO ND BY AFTERNOON IN RESPONSE TO A SURFACE
   CYCLONE PROGRESSING ENEWD ACROSS THE NRN PLAINS. STEEP MIDLEVEL
   LAPSE RATES OVERSPREADING THE MOIST LAYER COMBINED WITH TEMPERATURES
   IN THE LOW TO MID 80S WILL YIELD MLCAPE VALUES FROM 2000-3000 J/KG.
   WARM LAYER NEAR 800 MB WILL ACT TO CAP SURFACE BASED THUNDERSTORM
   DEVELOPMENT THROUGH EARLY AFTERNOON...BUT LARGE-SCALE ASCENT
   ASSOCIATED WITH THE APPROACHING TROUGH AND INCREASING LOW-LEVEL
   CONVERGENCE INVOF THE SURFACE LOW AND COLD FRONT WILL SUPPORT
   SCATTERED THUNDERSTORM DEVELOPMENT FROM MID AFTERNOON INTO THE
   NIGHT.

   BACKED SURFACE WINDS AHEAD OF THE SURFACE LOW AND ALONG THE WARM
   FRONT SURMOUNTED BY 30 KT LLJ...AND 40 KT MIDLEVEL SWLYS WILL FAVOR
   SUPERCELLS AND A THREAT FOR LARGE HAIL. ENHANCED LOW-LEVEL SHEAR
   NEAR THE WARM FRONT WILL PROMOTE A RISK FOR AN ISOLATED TORNADO OR
   TWO AS WELL. HOWEVER...MODERATELY STRONG MIDLEVEL SWLYS MAY ADVECT
   STORMS INTO A COOLER MORE STABLE BOUNDARY LAYER AIRMASS RATHER
   QUICKLY...WHICH WOULD PRECLUDE A MORE SUBSTANTIAL THREAT. AS THE
   UPPER TROUGH AND SURFACE COLD FRONT CONTINUE TO ADVANCE EWD INTO THE
   AREA AFTER DARK...STORM MERGERS WILL RESULT IN UPSCALE GROWTH WITH
   AT LEAST AN ISOLATED SEVERE WEATHER THREAT PERSISTING INTO WRN/NRN
   MN.

   ...CNTRL SD INTO NERN CO...
   ISOLATED HIGH BASED THUNDERSTORMS ARE FORECAST TO DEVELOP OVER THE
   CNTRL HIGH PLAINS THIS AFTERNOON ALONG AND AHEAD OF A SURFACE COLD
   FRONT. LOW-LEVEL SWLY WINDS WILL PROMOTE STRONG BOUNDARY LAYER
   MIXING WITH TEMPERATURES IN THE MID TO UPPER 80S AND DEWPOINTS IN
   THE 40S TO LOW 50S. AS A RESULT...MLCAPE VALUES WILL REMAIN NEAR 500
   J/KG DESPITE THE PRESENCE OF STEEP MIDLEVEL LAPSE RATES. A COUPLE OF
   SEVERE STORMS WILL BE POSSIBLE...MAINLY IN THE FORM OF DAMAGING
   WINDS...DUE TO THE PRESENCE OF INVERTED-V BOUNDARY LAYER PROFILES
   AND DEEP-LAYER SHEAR UP TO 30 KT. ADDITIONAL ISOLATED STORMS MAY
   ALSO DEVELOP ALONG A PSEUDO DRYLINE BOUNDARY EXTENDING SWD FROM
   CNTRL SD INTO CNTRL NEB. DEWPOINTS HERE WILL BE IN THE LOW
   60S...WHICH WILL YIELD MODERATE TO STRONG CAPE VALUES. SSWLY
   LOW-LEVEL WINDS VEERING TO WSWLY IN THE MIDLEVELS MAY SUPPORT BRIEF
   STORM ORGANIZATION AND A THREAT FOR LARGE HAIL.

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