TEXT FORECAST

SPC AC 280533
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1233 AM CDT THU AUG 28 2008
VALID 281200Z - 291200Z
...THERE IS A SLGT RISK OF SVR TSTMS SRN KS TO WRN LM...
...SYNOPSIS...
IN MID-UPPER LEVELS...PROGRESSIVE NRN STREAM PATTERN FCST TO
CONTINUE THROUGH PERIOD. WELL-DEFINED TROUGHING -- NOW EXTENDING
FROM UPPER LOW OVER FAR NRN MB SSWWD ACROSS CENTRAL HIGH PLAINS --
IS EXPECTED TO SHIFT EWD ACROSS UPPER GREAT LAKES REGION. THIS WILL
OCCUR AS REINFORCING SHORTWAVE PERTURBATION -- NOW SUBTLY EVIDENT IN
MOISTURE CHANNEL IMAGERY OVER MT -- DIGS ESEWD ACROSS DAKOTAS AND
MERGES WITH VORTICITY LOBE TRAILING SWWD FROM LEAD SHORTWAVE NOW
OVER ND. RESULTANT/BLENDED SHORTWAVE TROUGH SHOULD MOVE EWD ACROSS
UPPER MS VALLEY DURING DAY...THEN WEAKEN SOMEWHAT AS IT EJECTS NEWD
ACROSS ERN UPPER MI/NRN LOWER MI REGION BY 29/12Z.
MEANWHILE...WEAKNESS IN 500 MB HEIGHT FIELDS WILL PERSIST ACROSS
CENTRAL/SRN APPALACHIANS REGION...WITH EMBEDDED VORTICITY LOBES
CONTRIBUTING POCKETS OF LARGE SCALE ASCENT IN SUPPORT OF GEN TSTM
ENVIRONMENT THERE. LOW LEVEL REMAINS OF TS FAY SHOULD CONTINUE TO
WEAKEN SLOWLY AND DRIFT NEWD. FARTHER W...MID/UPPER RIDGING WILL
PERSIST FROM PACIFIC OFFSHORE N-CENTRAL CA...EWD ACROSS GREAT BASIN
AND 4-CORNERS REGIONS TO OZARKS. DIFFUSE/ELONGATED UPPER CYCLONE --
WITH CENTERS NOW EVIDENT OVER SRN NM AND NRN SONORA -- WILL DRIFT
ERRATICALLY OVER THAT REGION THROUGH DAY-1 PERIOD.
...UPPER GREAT LAKES TO S-CENTRAL PLAINS...
SCATTERED-NUMEROUS TSTMS FCST TO DEVELOP DURING AFTERNOON IN COLD
FRONTAL ZONE...PERHAPS COALESCING INTO NEARLY CONTINUOUS ARC FROM
UPPER MI TO KS FOR BRIEF INTERVAL BEFORE BREAKING UP INTO SHORTER
CLUSTERED SEGMENTS DURING EVENING. DAMAGING GUSTS AND LARGE HAIL
WILL BE POSSIBLE. SHORTWAVE TROUGH MOVING ACROSS MN WILL LEAD TO
ENHANCED HEIGHT GRADIENTS ALOFT AND STRENGTHENING BUT STILL DIFLUENT
UPPER FLOW OVER MUCH OF UPPER GREAT LAKES AND UPPER MS VALLEY
REGION...BENEATH AND E OF 100-110 KT 250 MB JET AND 60-70 KT 500 MB
SPEED MAX. ALTHOUGH PREFRONTAL SFC WINDS AND CAPE OVER THIS AREA
EACH ARE FCST TO BE WEAK...STRENGTH OF FLOW ALOFT WILL LEAD TO
FAVORABLE DEEP-LAYER SHEAR...AND SOME POTENTIAL FOR DAMAGING WIND
WITH BOW/LEWP FORMATIONS IN CONVECTIVE LINE.
MEANWHILE STRONGEST BUOYANCY IS EXPECTED FARTHER SW ACROSS PORTIONS
KS/MO/IL...WHERE STG SFC HEATING...MORE ROBUST MIDLEVEL LAPSE
RATES...AND SFC DEW POINTS UPPER 60S TO 70S F COULD YIELD MLCAPES IN
2000-3000 J/KG RANGE. WHILE PREFRONTAL AIR MASS FROM SRN KS EWD TO
W-CENTRAL IL WILL BE CHARACTERIZED BY WEAK LOW LEVEL
WINDS...POTENTIAL EXISTS FOR STORMS TO FORM IN AIR IMMEDIATELY
BEHIND SFC FRONT WHERE CONSIDERABLE MLCAPES STILL ARE PRESENT. THIS
REGIME MAY HELP SVR POTENTIAL BY MEANS OF NLY/NELY SFC WINDS
ENLARGING HODOGRAPH...ESPECIALLY FOR STORMS MOVING SE TO
SSE...THOUGH MIDLEVEL WINDS SHOULD BE WEAK. PRIMARY STORM MODE
SHOULD BE MULTICELLULAR...THOUGH BRIEF SUPERCELL STRUCTURES ARE
POSSIBLE. CONVECTIVE COVERAGE MAY DIMINISH FARTHER WSWWD INTO SWRN
KS AND NERN NM REGION...BUT MOST INTENSE CELLS STILL MAY BE CAPABLE
OF GUSTS/HAIL NEAR SVR LEVELS DURING LATE AFTERNOON.
...AZ....
ANOTHER ROUND OF SCATTERED TSTMS SHOULD DEVELOP AS DIURNAL HEATING
AND MIXING OCCUR WITHIN MOIST BOUNDARY LAYER....CHARACTERIZED BY
SFC DEW POINTS MID 60S DESERT VALLEYS AND PW AROUND 1.5 INCHES.
MAGNITUDE AND DISTRIBUTION OF STRONGEST HEATING WILL DEPEND ON
THICKNESS/LONGEVITY OF CLOUD COVER LEFT BEHIND BY PRIOR
CONVECTION...BUT AREAS THAT CAN REACH UPPER 90S OR HIGHER SFC TEMPS
WILL PRESENT MOST FAVORABLE SUBCLOUD LAYERS FOR STG-SVR GUSTS TO
REACH SFC. SOMEWHAT DEEPER LAYER OF TIGHTER MIDLEVEL ELY-ENELY
GRADIENT WINDS IS PROGGED THAN PERVIOUS DAY...AROUND NWRN RIM OF
COMPLEX UPPER LOW...WITH ENE WINDS ALOFT POSSIBLE DEVELOPING SEWD
THROUGH TUS AREA AS WELL. THIS INDICATES CONDITIONAL POTENTIAL FOR
BETTER ORGANIZED/AMALGAMATED OUTFLOW DEVELOPMENT OFF HIGHER TERRAIN.
CATEGORICAL UPGRADE MAY BE NEEDED IN SUCCEEDING OUTLOOKS GIVEN
DEPTH/STRENGTH OF FCST WINDS ALOFT TODAY.
...CENTRAL/ERN NC AND VICINITY...
AS REMAINS OF FAY CONTINUE TO SPIN DOWN ABOVE SFC...HODOGRAPH SIZE
SHOULD SHRINK COMMENSURATELY WITH TIME. STG VEERING WITH HEIGHT BUT
WEAK ABSOLUTE SPEEDS ARE FCST IN BOUNDARY LAYER ALONG AND N OF SFC
FRONTAL ZONE...EXTENDING EWD FROM CENTRAL PORTIONS OF SLOW-MOVING
REMAINS OF TS FAY. GIVEN RELATED WEAKNESS OF LOW LEVEL
WINDS...SUPERCELL OCCURRENCE AND RELATED TORNADO RISK WILL NEED
CONSIDERABLY MORE MESOBETA TO STORM SCALE HELP THAN IN PREVIOUS DAYS
-- EVEN INVOF SFC FRONTAL ZONE. THEREFORE ONLY VERY MRGL TORNADO
PROBABILITIES ARE FCST ATTM.
..EDWARDS/BRIGHT.. 08/28/2008