SWODY1
SPC AC 091242
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0742 AM CDT THU SEP 09 2010
VALID 091300Z - 101200Z
...THERE IS A SLGT RISK OF SVR TSTMS THIS AFTERNOON INTO TONIGHT
OVER PART OF THE NRN INTO CNTRL HIGH PLAINS...
...NRN INTO CNTRL HIGH PLAINS...
POTENT VORTICITY MAXIMUM AND ASSOCIATED 100+ KT UPPER-LEVEL JET
STREAK CURRENTLY ROUNDING THE LARGE-SCALE TROUGH BASE OVER NV WILL
TRANSLATE NEWD INTO THE REGION...RESULTING IN A CONSIDERABLE
INCREASE IN DYNAMIC FORCING FOR ASCENT DURING THE LATTER HALF OF THE
DIURNAL HEATING CYCLE. THIS WILL HASTEN THE DEEPENING OF A LEE
CYCLONE OVER NERN WY/SERN MT TODAY...PRIOR TO THE LOW ACCELERATING
NNEWD INTO SERN SASKATCHEWAN OVERNIGHT. AN ASSOCIATED LEE TROUGH OR
DRYLINE WILL REMAIN QUASI-STATIONARY OVER ERN PARTS OF WY/CO WHILE A
WARM FRONT SLOWLY LIFTS NWD THROUGH THE DAKOTAS. FARTHER W...A COLD
FRONT WILL STRENGTHEN WHILE PROGRESSING EWD/SEWD THROUGH THE NRN
HIGH PLAINS.
THE DEEPENING SURFACE CYCLONE WILL SERVE TO ENHANCE SELY LOW-LEVEL
FLOW...MAINTAINING AN AXIS OF UPPER 50S/LOWER 60S BOUNDARY LAYER DEW
POINTS E OF THE SHARPENING LEE TROUGH/DRYLINE. THIS MOISTURE AXIS
WILL COINCIDE WITH A STEEP MIDLEVEL LAPSE RATE/EML PLUME PRECEDING
WRN U.S. UPPER TROUGH...SUPPORTING AFTERNOON MLCAPE VALUES OF
1000-2000 J/KG. LATEST MODEL GUIDANCE IS CONSISTENT IN SUGGESTING
THAT THE COMBINED EFFECTS OF THE ABOVE-MENTIONED INCREASE IN
LARGE-SCALE FORCING AND SUSTAINED SURFACE CONVERGENCE ALONG LEE
TROUGH/DRYLINE WILL ERODE THE CAP WITHIN A NARROW N-S CORRIDOR OVER
THE WRN DAKOTAS INTO THE NEB PNHDL...ALLOWING FOR ISOLATED TO
SCATTERED STORM FORMATION BY LATE AFTERNOON OR EARLY EVENING.
SWLY MIDLEVEL FLOW STRENGTHENING TO 45-55 KT ATOP A SELY LOW-LEVEL
WIND FIELD WILL RESULT IN VERTICAL SHEAR MORE THAN SUFFICIENT FOR
SUPERCELLS CAPABLE OF LARGE HAIL AND LOCALLY DAMAGING WIND GUSTS. A
TORNADO OR TWO IS POSSIBLE WITH ANY SUPERCELLS THAT CAN REMAIN FULLY
SURFACE-BASED BEYOND 10/00Z WHEN LOW-LEVEL SHEAR WILL NOTABLY
INCREASE IN CONJUNCTION WITH THE DEVELOPMENT OF A 40-50 KT LLJ.
ADDITIONAL DIURNALLY-ENHANCED STORMS WILL BE POSSIBLE FARTHER W
ALONG OR IN WAKE OF COLD FRONT OVER MT WHERE SHEAR WILL BE
STRONG...BUT INSTABILITY SOMEWHAT MARGINAL. ISOLATED HAIL AND/OR
DAMAGING WIND EVENTS MAY ACCOMPANY ANY MORE SUSTAINED STORMS IN THIS
AREA.
...OZARK PLATEAU...
THE REMNANT CIRCULATION OF TROPICAL STORM HERMINE CURRENTLY OVER
N-CNTRL OK WILL UNDERGO CONSIDERABLE WEAKENING TODAY AS SYSTEM IS
ENTRAINED INTO THE WESTERLIES AND SUBSEQUENTLY ACCELERATES NEWD
THROUGH THE OZARKS. HOWEVER...AREA PROFILER AND VWP DATA SHOW THAT
A BELT OF MODERATELY STRONG /40-50 KT/ LOW TO MID-TROPOSPHERIC FLOW
HAS BEEN MAINTAINED WITHIN ERN SEMICIRCLE OF LARGE-SCALE
CIRCULATION. SIMILAR TO THE PAST COUPLE OF DAYS...THIS ENHANCED
WIND FIELD COMBINED WITH A MOIST BOUNDARY LAYER AND THE ONSET OF
DAYTIME HEATING MAY YIELD AN ENVIRONMENT SUPPORTIVE OF A FEW
SUPERCELLS CAPABLE OF A BRIEF TORNADO OR TWO...DESPITE THE OVERALL
WEAKENING AND TRANSITION OF SYSTEM TO EXTRATROPICAL.
..MEAD/GRAMS.. 09/09/2010
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