SPC AC 271728
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1228 PM CDT TUE AUG 27 2013
VALID 281200Z - 291200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
AN EXPANSIVE MID-LEVEL ANTICYCLONE WILL PERSIST ACROSS MUCH OF THE
CONUS INTO WED. MEANWHILE...A DISORGANIZED IMPULSE ON THE E SIDE OF
THE ANTICYCLONE WILL MOVE SEWD FROM THE GREAT LAKES REGION TO THE
MID ATLANTIC AND OFF THE COAST...SERVING TO MAINTAIN A
HIGHER-AMPLITUDE TROUGH OVER THE WRN ATLANTIC WATERS. A WEAK COLD
FRONT ACCOMPANYING THIS IMPULSE WILL SHIFT SWD ACROSS PARTS OF THE
GREAT LAKES...OHIO VALLEY...AND NORTHEAST STATES...WHILE THE SAME
BOUNDARY TRAILS NWWD INTO THE NRN PLAINS. OTHER PERTURBATIONS
EMBEDDED WITHIN A MERIDIONALLY- EXTENSIVE...WRN-CONUS MONSOONAL
MOISTURE PLUME WILL TRACK AROUND THE NRN FLANK OF THE ANTICYCLONE
FROM THE NRN ROCKIES TO THE ADJACENT PLAINS.
...NRN ROCKIES AND NRN PLAINS TO IA...
CONVECTION MAY BE ONGOING AT THE BEGINNING OF THE PERIOD OVER PARTS
OF THE DAKOTAS IN A WEAK WARM ADVECTION REGIME...BUT SHOULD WEAKEN
THROUGH THE MORNING. MEANWHILE...THE AFOREMENTIONED FRONT WILL
GRADUALLY EDGE NWD OR REMAIN QUASI-STATIONARY THROUGH THE DAY.
LOW-LEVEL ASCENT INVOF THIS FEATURE MAY BE BOLSTERED BY DIFFERENTIAL
HEATING ACCOMPANYING REMNANTS OF PREVIOUS CONVECTION AND ITS
ASSOCIATED OUTFLOW BOUNDARIES TO SUPPORT CONVECTIVE DEVELOPMENT
DURING THE AFTERNOON FROM PARTS OF ERN MT ACROSS THE DAKOTAS INTO
IA. THE COMBINATION OF MODERATE TO STRONG DESTABILIZATION WITHIN THE
MOIST BOUNDARY LAYER N OF THE FRONT...AND MODEST DEEP SHEAR OWING TO
20-25-KT WLY/S OVERLYING GENERALLY WEAK ESELY LOW-LEVEL FLOW...MAY
SUPPORT A FEW ORGANIZED CONVECTIVE STRUCTURES. SPORADIC/MARGINAL
SVR/WIND HAIL POSSIBLE WILL BE POSSIBLE INTO THE EVENING HOURS.
ADDITIONAL CONVECTION IS EXPECTED TO DEVELOP WITHIN THE MONSOONAL
MOISTURE PLUME FROM THE MOUNTAINS OF CNTRL ID TO SWRN MT DURING THE
AFTERNOON...AND GRADUALLY MOVE OVER THE LOWER PLAINS OF MT IN THE
EVENING. SOME INTENSIFICATION TO MID-LEVEL FLOW MAY YIELD SUFFICIENT
DEEP SHEAR FOR A FEW MULTICELLS...WITH THE POTENTIAL FOR MICROBURSTS
TO PRODUCE AN ISOLATED SVR GUST AIDED BY STEEP LOW/MID-LEVEL LAPSE
RATES. THIS ACTIVITY COULD SPREAD ACROSS PARTS OF THE DAKOTAS
OVERNIGHT WED NIGHT.
LARGE-SCALE/DEEP FORCING FOR ASCENT WILL BE GENERALLY LIMITED/SUBTLE
WITHIN BOTH REGIMES...WHICH BREEDS LOW CONFIDENCE IN THE
IDENTIFICATION OF ANY CORRIDORS OF GREATER SVR POTENTIAL.
ISOLATED CONVECTION MAY ALSO DEVELOP INVOF THE BOUNDARY INTO IA
DURING THE AFTERNOON...AND A CONDITIONAL/ISOLATED SVR-WIND THREAT
CANNOT BE RULED OUT WITH THIS ACTIVITY. WARM MID-LEVEL CONDITIONS
MAY PROVE HOSTILE TO THE MAINTENANCE OF ANY INTENSE CONVECTION IN
IA...PRECLUDING THE INTRODUCTION OF SVR PROBABILITIES.
...UPPER OH VALLEY TO THE MID ATLANTIC AND NE STATES...
WEAK FRONTAL CONVERGENCE ALONG WITH OROGRAPHIC EFFECTS AROUND THE
CNTRL APPALACHIANS WILL FOCUS THUNDERSTORM DEVELOPMENT THROUGH THE
DAY...AIDED BY ASCENT PRECEDING THE AFOREMENTIONED SHORTWAVE TROUGH.
THE ACTIVITY WILL HAVE A TENDENCY TO MOVE SEWD TOWARD THE COAST INTO
THE EVENING. MODESTLY ENHANCED MID-LEVEL FLOW WILL CONTRIBUTE TO
EFFECTIVE BULK WIND DIFFERENCES AROUND 25 KT TO SUPPORT MULTICELL
CLUSTERS AND ISOLATED DMGG WIND FROM THE UPPER OH VALLEY TO THE MID
ATLANTIC. WITH FAIRLY RICH TROPOSPHERIC MOISTURE SUPPORTING PW
GENERALLY AOA 1.8 INCHES...ABUNDANT WATER-LOADING COULD ENHANCED THE
POTENTIAL FOR STRONG DOWNBURSTS. THE LACK OF STRONGER DEEP SHEAR AND
WEAK MID-LEVEL LAPSE RATES ARE CURRENTLY EXPECTED TO PREVENT A MORE
SUBSTANTIAL SVR THREAT FROM EVOLVING. FARTHER N INTO THE NE
STATES...THUNDERSTORMS SHOULD LACK ORGANIZATION OWING TO WEAK DEEP
SHEAR ASSOCIATED WITH WEAKER MID-LEVEL FLOW.
...PORTIONS OF AZ AND SERN CA...
MONSOONAL MOISTURE/PW WILL INCREASE THROUGH THE DAY...WITH
OROGRAPHIC ASCENT EXPECTED TO ENCOURAGE THUNDERSTORM DEVELOPMENT
OVER THE MOUNTAINS. STORMS COULD ADVANCE OVER THE LOWER ELEVATIONS
DURING THE AFTERNOON AND EVENING WITH STRONG WIND GUSTS POSSIBLE.
WEAK MID-LEVEL LAPSE RATES AND WEAK TROPOSPHERIC FLOW SHOULD LARGELY
MITIGATE THE SVR POTENTIAL.
..COHEN/GOSS.. 08/27/2013
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