SPC AC 181236
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0736 AM CDT TUE AUG 18 2009
VALID 181300Z - 191200Z
...THERE IS A SLGT RISK OF SVR TSTMS PARTS OF THE SRN/CENTRAL HIGH
PLAINS...
...SRN/CENTRAL HIGH PLAINS...
WITH LITTLE CHANGE IN THE OVERALL SYNOPTIC PATTERN ACROSS THIS
REGION...SEVERE THREAT AREAS WILL BE MITIGATED BY PRECEEDING
THUNDERSTORMS AND LOCATION OF RESIDUAL OUTFLOW BOUNDARIES LATER
TODAY. MODELS FAIL TO PROPERLY HANDLE EARLY MORNING MCS OVER OK AND
ITS EXPECTED SUPPRESSION OF MOIST/UNSTABLE AIR MASS SWD INTO WRN
TX/SERN OK THIS MORNING. THIS GIVES LITTLE CREDENCE TO MODEL
FORECAST OF MODERATE TO STRONG INSTABILITY FROM CENTRAL/NWRN OK INTO
NERN NM/SERN CO LATER TODAY...AND WOULD NOT BE SURPRISED TO SEE THIS
AXIS DEVELOP FARTHER SSW THAN CURRENTLY PROGGED. EXPECT LEADING LINE
AHEAD OF ONGOING MCS WILL CONTINUE SHIFTING ESEWD INTO SRN/ERN OK
THIS MORNING...ALTHOUGH SHEAR WEAKENS WITH SEWD EXTENT AND MAY TEND
TO WEAKEN OVERALL ORGANIZATION OF THIS ACTIVITY. AN ISOLATED
STRONG/SEVERE STORM COULD ACCOMPANY THE MORNING MCS...BUT OVERALL
SEVERE THREAT SHOULD BE LIMITED FOR MUCH OF THE DAY.
GREATER THREAT SHOULD EVOLVE NEAR THE HIGHER TERRAIN OF NRN
NM/SRN-CENTRAL CO DURING THE MID TO LATE AFTERNOON AS PRONOUNCED
SHORTWAVE TROUGH NOW OVER ERN UT/WRN CO SHIFTS EWD ACROSS CO. DEEP
ASCENT AHEAD OF THIS WELL DEFINED VORT MAX MAY SUPPORT EARLIER
DEVELOPMENT OVER THE HIGH PLAINS AS COMPARED TO THE PAST FEW DAYS.
AIRMASS JUST EAST OF THE HIGH TERRAIN WILL BE QUITE MOIST AND SHOULD
DESTABILIZE SUFFICIENTLY FOR SEVERAL CLUSTERS OF SEVERE STORMS
SPREADING ESEWD THROUGH THE EVENING. AS WAS THE CASE MONDAY...SHEAR
WILL BE MORE THAN SUFFICIENT FOR SUPERCELLS WITH THREATS OF LARGE
HAIL...INCLUDING ISOLATED SIGNIFICANT HAIL...AND ISOLATED DAMAGING
WINDS WITHIN VERY STEEP LAPSE RATES OVER THE HIGH PLAINS.
INCREASING SLY LLJ LATE TODAY/THIS EVENING AHEAD OF MID LEVEL
SHORTWAVE TROUGH SHOULD ALSO SUPPORT AN ISOLATED TORNADO THREAT AS
LOW LEVEL SHEAR STRENGTHENS OVER THE HIGH PLAINS.
ADDITION DEVELOPMENT MAY OCCUR LATE TODAY INVOF SURFACE OUTFLOW
BOUNDARY AS CAP WEAKENS. ALTHOUGH CONFIDENCE IN PLACING THIS
BOUNDARY REMAINS LOW ATTM...WRN PORTION MAY ERODE/LIFT NWD INTO THE
TX PANHANDLE/WRN OK BY LATE IN THE DAY. INCREASING SLY LLJ ACROSS
THE SRN HIGH PLAINS OVERNIGHT SHOULD ONCE AGAIN SUPPORT MCS ACTIVITY
TRACKING ESEWD TONIGHT WITH SEVERE THREAT GRADUALLY DIMINISHING
DURING THE MID TO LATE EVENING.
...WRN NEB INTO THE CENTRAL/ERN DAKOTAS...
NRN STREAM TROUGH ALOFT WILL REMAIN POSITIVELY-TILTED ACROSS THIS
REGION TODAY WITH A SERIES OF COMPACT SHORTWAVE TROUGHS DIGGING
SEWD. THIS WILL SUSTAIN ASCENT ATOP DEVELOPING MARGINAL INSTABILITY
THIS AFTERNOON ACROSS THIS REGION...WITH MODELS CONSISTENT IN
DEVELOPING DIURNAL THUNDERSTORMS INVOF SSW-NNE ORIENTED SURFACE
TROUGH FROM THE CENTRAL HIGH PLAINS TOWARDS SERN ND. SHEAR REMAINS
FAIRLY STRONG AND SHOULD SUPPORT A FEW ORGANIZED STORMS...ALTHOUGH
SEVERITY MAY BE TEMPERED BY RELATIVELY DRY BOUNDARY LAYER AND
RESULTANT WEAK TO MARGINAL INSTABILITY INTO THE DAKOTAS.
...OZARK REGION INTO THE OH VALLEY AND LOWER GREAT LAKES...
AXIS OF LOW LEVEL MOISTURE IS ALREADY IN PLACE WITH DEEP MOISTURE
PLUME EVIDENT ON GOES-PW DATA/MORNING SOUNDINGS FROM ERN OK/SERN KS
THROUGH THE OH VALLEY INTO THE LOWER GREAT LAKES REGION. ALTHOUGH
LAPSE RATES WILL REMAIN QUITE WEAK WITHIN THIS MOISTURE
PLUME...SUFFICIENT HEATING AND ASCENT AHEAD OF SURFACE FRONT SHOULD
SUPPORT SCATTERED THUNDERSTORMS AND MODEST INSTABILITY THIS
AFTERNOON OVER THIS LARGE REGION. EFFECTIVE BULK SHEAR OF 25-30 KT
SUGGESTS POTENTIAL FOR MULTICELLS WITH LOCALLY STRONG WIND GUSTS
BEING THE PRIMARY THREAT WITH THE MORE ORGANIZED STORMS TODAY.
..EVANS/JEWELL.. 08/18/2009
CLICK TO GET WUUS01 PTSDY1 PRODUCT
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1630Z
|