SWODY1
SPC AC 020539
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1239 AM CDT WED SEP 02 2009
VALID 021200Z - 031200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE CENTRAL PLAINS...
...SYNOPSIS...
AN AMPLIFIED LONGWAVE REGIME WILL CONTINUE TODAY WITH WEAK
WESTERLIES OVER THE CONUS. AS MEAN UPPER TROUGHING REMAINS OVER THE
EASTERN HALF OF THE CONUS...PERSISTENT UPPER LOW WILL CONTINUE TO
TRANSITION ESE OVER THE MIDDLE MO RIVER VALLEY TODAY. A MODESTLY
AMPLIFYING UPPER RIDGE WILL PREVAIL OVER THE ROCKIES AHEAD OF AN
UPPER TROUGH REACHING THE PACIFIC NORTHWEST...ALL WHILE HURRICANE
JIMENA MOVES ACROSS THE BAJA PENINSULA /REFERENCE LATEST NHC
GUIDANCE/.
...PLAINS...
AFOREMENTIONED MIGRATORY UPPER LOW CROSSING THE MIDDLE MO RIVER
VALLEY WILL BE THE MAIN IMPETUS FOR TSTM DEVELOPMENT /SOME STRONG TO
SEVERE/ ACROSS THE NORTH CENTRAL PLAINS TODAY...ESPECIALLY THIS
AFTERNOON/EVENING ACROSS SOUTHERN SD AND CENTRAL/EASTERN NEB.
MOISTURE WILL REMAIN RELATIVELY MODEST THROUGH THE PERIOD ACROSS THE
REGION...BUT THE COMBINATION OF 50S F SURFACE DEWPOINTS AND
RELATIVELY COOL THERMAL PROFILES ALOFT/STEEP LAPSE RATES SHOULD
SUPPORT A LARGELY DIURNAL RISK FOR SEVERE HAIL/GUSTY WINDS IN
VICINITY OF A NORTH-SOUTH SURFACE TROUGH/WEAK FRONT AND ASSOCIATED
MOISTURE/INSTABILITY AXIS. WITH PERHAPS AS MUCH AS 1000-1500 J/KG OF
MLCAPE BY MID AFTERNOON...LOWER TROPOSPHERIC VEERING BENEATH A BELT
OF 40 KT WNW MID LEVEL FLOW ON THE SOUTHERN PERIPHERY OF THE UPPER
LOW WOULD SUPPORT MAINLY MULTICELLS/PERHAPS A FEW SUPERCELLS INTO
EARLY EVENING...WITH THE SEVERE THREAT EXPECTED TO DIMINISH
THEREAFTER AS THE BOUNDARY LAYER COOLS.
REMOVED FROM THE UPPER LOW/SPEED MAX...THE CONTINUED EASTWARD
ADVECTION OF A STOUT ELEVATED MIXED LAYER /AND MODEST MOISTURE/ WILL
LIKELY CAP AREAS SOUTH OF THE NEB/KS BORDER OR I-70 VICINITY...ASIDE
FROM DIURNAL DEVELOPMENT ALONG THE HIGHER TERRAIN OF THE SOUTH
CENTRAL HIGH PLAINS. ACCORDINGLY...TSTMS SHOULD AGAIN DEVELOP ACROSS
SOUTHEAST CO/FAR NORTHEAST NM BY LATE AFTERNOON VIA DIFFERENTIAL
HEATING ALONG THE HIGHER TERRAIN AND MOIST LOW LEVEL UPSLOPE...WITH
SUBSEQUENT DEVELOPMENT INTO THE OK/TX PANHANDLES AND SOUTHWEST KS
WITHIN A DEEPLY MIXED BOUNDARY LAYER. SEVERE HAIL/GUSTY WINDS WILL
BE POSSIBLE WITH THE STRONGEST STORMS DURING THE AFTERNOON/EARLY
EVENING...BUT PROXIMITY OF THE ROCKIES UPPER RIDGE AND WEAK LOW/MID
TROPOSPHERIC FLOW SHOULD PRECLUDE AN ORGANIZED SEVERE RISK.
...SOUTHERN AZ...
WITH SCATTERED LATE NIGHT TSTMS AND DERIVED GPS PW DATA INDICATIVE
OF AROUND 2 INCH VALUES ACROSS NORTHWEST MEXICO...MOISTURE SEEMS
LIKELY TO CONTINUE TO INCREASE INTO SOUTHERN AZ THROUGH THE PERIOD
AS JIMENA PROGRESSES GENERALLY NORTHWARD ALONG THE BAJA PENINSULA.
SUBSIDENCE/SLIGHTLY WARMING MID LEVEL THERMAL PROFILES MAY CURB THE
EXTENT OF DEEP CONVECTIVE DEVELOPMENT...AND STEERING FLOW OFF THE
HIGHER TERRAIN IS EXPECTED TO BE WEAK. NONETHELESS...THE POTENTIAL
FOR AN INCREASINGLY MOIST/UNSTABLE AIRMASS ACROSS SOUTHERN
/ESPECIALLY SOUTHWEST/ AZ WARRANTS MODEST PROBABILITIES FOR STRONG
OUTFLOW WINDS/BLOWING DUST.
..GUYER/GARNER.. 09/02/2009
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