SWODY1
SPC AC 301252
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0752 AM CDT SAT AUG 30 2008
VALID 301300Z - 311200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
NRN STREAM PATTERN WILL REMAIN PROGRESSIVE THROUGH PERIOD. AS A
PRECURSOR TO DEEP TROUGHING FCST TO DEVELOP IN SUBSEQUENT DAYS
ACROSS ERN CONUS...EXPECT HEIGHT FALLS AND TIGHTENING MID/UPPER
LEVEL HEIGHT GRADIENTS ACROSS MUCH OF NERN GREAT BASIN AND NRN
ROCKIES...AS TROUGHING SHIFTS EWD FROM NERN PACIFIC. AS THIS
OCCURS...RIDGING WILL BEGIN TO BREAK DOWN ACROSS 4-CORNERS
REGION...WITH PRIMARY ANTICYCLONE SHIFTING/REDEVELOPING EWD TO MID
MS VALLEY REGION. PERSISTENT/WEAK TROUGHING WILL REMAIN OVER SERN
CONUS.
AT SFC...FRONTAL ZONE IS EVIDENT FROM SRN ONT SWWD ACROSS OH AND SRN
OZARKS...OK...NERN NM. ERN PORTION OF FRONT WILL MOVE EWD ACROSS
NERN CONUS...WHILE TRAILING PORTION OVER LOWER MS VALLEY AND SRN
PLAINS BECOMES MORE ILL-DEFINED. SRN HIGH PLAINS SEGMENT OF THIS
FRONTAL ZONE SHOULD RETREAT NWD ACROSS ERN CO/WRN KS...DEMARCATING
NRN FRINGE OF SELY RETURN FLOW AT LEAST AS MUCH FOR MOISTURE AS FOR
THERMAL IDENTITY OF AIR MASS. THIS WILL OCCUR IN RESPONSE TO
COMBINATION OF LEE-SIDE AND FRONTAL-WAVE CYCLOGENESIS ACROSS
S-CENTRAL/SERN MT. BY 31/00Z...STRENGTHENING FRONTAL ZONE WILL
EXTEND FROM SWRN MB SWWD THROUGH MT LOW ACROSS S-CENTRAL/SWRN MT AND
SRN ID...WITH LEE TROUGHING SSEWD ACROSS ERN WY AND ERN CO.
...NRN HIGH PLAINS...NRN ROCKIES...
ISOLATED TO WIDELY SCATTERED TSTMS MAY DEVELOP DURING AFTERNOON AND
PERSIST INTO EVENING ALONG OR BEHIND SFC COLD FRONT...IN ENVIRONMENT
CHARACTERIZED BY STRENGTHENING MID-UPPER LEVEL WINDS.
ASSOCIATED FAST MOVEMENT OF HIGH-BASED CONVECTION...MOVING OVER
DEEPLY MIXED SUBCLOUD LAYER...SUGGESTS POTENTIAL FOR STG/LOCALLY SVR
GUSTS WITH MOST PERSISTENT/INTENSE TSTMS. STG LIMITING FACTOR WILL
BE LACK OF MORE ROBUST LOW LEVEL MOISTURE...KEEPING BUOYANCY WEAK
AND LIMITING COVERAGE/DURATION OF TSTMS. FCST SOUNDINGS SUGGEST
MLCAPES LESS THAN 250 J/KG OVER MOST OF THIS REGION DURING MOST
UNSTABLE PERIOD OF MID-LATE AFTERNOON. TSTM COVERAGE MAY INCREASE
AFTER DARK IN ELEVATED WAA REGIME...WITH ISOLATED HAIL POSSIBLE IN
NE-SW ALIGNED BAND OF TSTMS. HOWEVER...MUCAPES STILL WILL BE RATHER
WEAK -- GENERALLY AOB 250 J/KG. GIVEN THESE CONCERNS...ORGANIZED
SVR THREAT APPEARS TOO MRGL/CONDITIONAL ATTM FOR PROBABILITIES
SUPPORTING CATEGORICAL OUTLOOK.
...MID MS VALLEY TO S-CENTRAL PLAINS...
WIDELY SCATTERED TO SCATTERED AFTERNOON TSTMS SHOULD DEVELOP INVOF
RESIDUAL FRONTAL ZONE. COMBINATION OF WEAK FRONTAL
CONVERGENCE...DIURNAL HEATING AND RICH BOUNDARY LAYER THETAE WILL
RESULT IN WEAK CINH AND TSTM INITIATION...SOME OF WHICH MAY EVOLVE
UPSCALE INTO A FEW OUTFLOW-DOMINANT/MULTICELLULAR CLUSTERS. MLCAPES
2500-3000 J/KG ARE POSSIBLE IN PRECONVECTIVE AIR MASS...BUT WITH
VERY WEAK DEEP-LAYER WINDS UNDER UPPER RIDGING...E.G. EFFECTIVE
SHEAR MAGNITUDES LESS THAN 5 KT IN NAM-KF FCST SOUNDINGS ACROSS MUCH
OF REGION.
...SWRN CONUS...
AFOREMENTIONED BREAKDOWN OF UPPER RIDGE WILL RESULT IN WEAKENING OF
HEIGHT GRADIENT ALOFT AND OF DEEP-LAYER BULK SHEAR...ALONG WITH
CONSIDERABLE VEERING/WEAKENING OF MIDLEVEL WINDS ACROSS CENTRAL/SRN
AZ. THERFORE...POTENTIAL FOR ORGANIZED CONVECTION IS FCST TO
DECREASE RELATIVE TO PREVIOUS DAYS...INCLUDING THREAT FOR TSTMS TO
PRODUCE AMALGAMATED OUTFLOWS ACROSS DESERTS. HOWEVER...FAVORABLE
LOW LEVEL MOISTURE AND HEATING OF HIGHER TERRAIN SHOULD YIELD WIDELY
SCATTERED TO SCATTERED TSTMS DURING MID-LATE AFTERNOON. STRONGEST
OF THESE MAY PRODUCE HAIL/GUSTS NEAR SVR LEVELS.
...LOWER-MIDDLE FL KEYS...
NHC TRACK AND WIND RADII FCSTS INDICATE CENTER OF GUSTAV WILL PASS
WELL SW OF THIS REGION...BUT THAT PERIPHERAL NERN QUADRANT OF
CIRCULATION ENVELOPE MAY BRUSH ACROSS KEYS MAINLY DURING LATTER HALF
OF PERIOD. FCST HODOGRAPHS SUGGEST CONSIDERABLE TURNING WITH HEIGHT
IN LOW LEVELS...EXPANDING IN SIZE WITH SWWD EXTENT DOWN KEYS. A FEW
SUPERCELLS ARE POSSIBLE WITHIN OUTERMOST BANDS...AS WELL AS SOME
POTENTIAL FOR ROTATION WITH ANY RELATIVELY DISCRETE/PERSISTENT
CELLS. THEREFORE...WILL INTRODUCE MRGL/SUB-CATEGORICAL TORNADO
PROBABILITIES ATTM. ANY EXPANSION/INTENSIFICATION OF PERIPHERAL LOW
LEVEL WINDS OR RIGHTWARD SHIFT IN PATH WOULD INCREASE TORNADO
THREAT...AND DECREASE PROBABILITIES WITH MORE WWD TRACK OR
WEAKER/SMALLER WIND ENVELOPE.
..DIAL/EDWARDS/CROSBIE.. 08/30/2008
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