SPC AC 070557
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1257 AM CDT THU AUG 07 2008
VALID 071200Z - 081200Z
...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS CAROLINAS TO
MID-SOUTH...
...SYNOPSIS...
SEASONALLY HIGH-AMPLITUDE UPPER AIR PATTERN OVER CONUS WILL BE
DOMINATED BY ANTICYCLONE CENTERED OVER SRN ROCKIES REGION. MEAN
TROUGHS WILL PERSIST FROM HUDSON BAY VORTEX SWD OVER LOWER GREAT
LAKES/CENTRAL APPALACHIAN REGIONS...AND OVER NERN PACIFIC. BROAD
MID-UPPER LEVEL CYCLONE -- NOW EVIDENT IN MOISTURE CHANNEL IMAGERY
INVOF 50N143W -- IS EXPECTED TO MOVE SLOWLY EWD THROUGH PERIOD
TOWARD BC COAST...BUT REMAIN OFFSHORE UNTIL AT LEAST LATE DAY-2.
MEANWHILE...SHORTWAVE TROUGH IS FCST TO DIG SEWD FROM NWRN ONT
ACROSS UPPER GREAT LAKES...CLOSE TO MEAN TROUGH POSITION OVER
MID/UPPER OH VALLEY BY 8/12Z.
OUTSIDE PRIMARY FLOW BELT...CONVECTIVELY ENHANCED PERTURBATION --
ANALYZED ON 00Z 500 MB CHART OVER ERN UT -- SHOULD DRIFT NEWD
THROUGH MEAN UPPER RIDGE POSITION...ACROSS NWRN CO.
MEANWHILE...WARM-CORE MID-UPPER LEVEL VORTICITY LOBE -- LEFT OVER
FROM TS EDOUARD -- IS EXPECTED TO DRIFT WWD-WSWWD TOWARD SERN NM AND
GRADUALLY WEAKEN.
AT SFC...DIFFUSE FRONTAL ZONE -- NOW EVIDENT FROM LOW OFFSHORE SRN
NEW ENGLAND WSWWD OVER LOWER OH VALLEY TO SRN KS -- WILL BE
REINFORCED E OF MS RIVER AND MOVE SEWD INTO CENTRAL/SRN APPALACHIANS
BY 8/00Z. WRN SEGMENT OF FRONT SHOULD SAG SWD AND SWWD ACROSS MUCH
OF AR AND OK DURING THIS PERIOD AS WELL. CENTRAL/SRN PLAINS PORTION
OF THIS BOUNDARY WILL DIFFERENTIATE HOT/WELL-MIXED BOUNDARY LAYERS
TO ITS S FROM ELY/UPSLOPE MOIST ADVECTION REGIME TO ITS N. OCCLUDED
FRONT -- CONNECTING LOW S OF NEW ENGLAND WITH WEAKENING CYCLONE OVER
ST LAWRENCE VALLEY REGION OF SRN QUE...SHOULD MOVE
LITTLE...REMAINING NEAR SFC TROUGH AND WIND SHIFT ACROSS ERN NY AND
WRN NEW ENGLAND. QUASISTATIONARY SFC TROUGH WILL EXTEND FROM
ATLANTIC LOW SWWD ACROSS CAROLINAS AND ERN/SRN GA...AHEAD OF COLD
FRONT.
...CAROLINAS TO MID-SOUTH...
SCATTERED AND POSSIBLY NUMEROUS TSTMS IN CLUSTERS SHOULD DEVELOP
DURING AFTERNOON OVER PARTS OF THIS REGION. DAMAGING GUSTS WILL BE
GREATEST THREAT...THOUGH OCCASIONAL LARGE HAIL ALSO WILL BE POSSIBLE
FROM MOST INTENSE/DISCRETE ACTIVITY. STG SFC HEATING AND DEW POINTS
UPPER 60S TO MID 70S SHOULD OVERCOME WEAK LAPSE RATES ALOFT TO YIELD
MLCAPES 1000-2000 J/KG...ATOP MODERATELY WELL-MIXED BOUNDARY LAYER
SUPPORTING SVR GUSTS. DEEPENING TROUGH AND RELATED HEIGHT FALLS
OVER OH VALLEY AND CENTRAL APPALACHIANS ALSO SHOULD TIGHTEN HEIGHT
GRADIENTS JUST DOWNSTREAM...PLACING PORTIONS CAROLINAS IN SRN FRINGE
OF STRONGER FLOW ALOFT -- E.G. 35-45 KT 500 MB WLYS AND 50-70 KT 250
MB WINDS BY 8/00Z. WHILE LOW LEVEL FLOW IS FCST TO REMAN
WEAK...LIMITING HODOGRAPH SIZE AND VERTICAL SHEAR...ENHANCED SHEAR
THROUGH CLOUD-BEARING LAYER SHOULD ENHANCE MULTICELLULAR
ORGANIZATION AND ALSO YIELD BRIEF/CONDITIONAL SUPERCELL POTENTIAL
THAT MOST LIKELY WOULD BE TIED TO BOUNDARY INTERACTIONS.
...AR TO S-CENTRAL PLAINS...
FARTHER W...DEEP-LAYER FLOW IS EXPECTED TO WEAKEN STILL
FURTHER...LEADING TO PULSE AND DISORGANIZED MULTICELLULAR TSTM
MORPHOLOGIES. VERY RICH LOW LEVEL MOISTURE AND STG DIURNAL SFC
HEATING WILL COMBINE WITH LIFT INVOF FRONT TO WEAKEN
CAP...CONTRIBUTING TO DEVELOPMENT OF SCATTERED TO WIDELY SCATTERED
TSTMS MAINLY MID-LATE AFTERNOON. A FEW STG-SVR GUSTS CANNOT BE
RULED OUT FROM MOST INTENSE CELLS...HOWEVER...ORGANIZED SVR THREAT
APPEARS TOO MRGL FOR CATEGORICAL OUTLOOK ATTM.
...CENTRAL HIGH PLAINS...
SCATTERED-NUMEROUS TSTMS AGAIN SHOULD DEVELOP OVER PORTIONS CO/NM
AND PERHAPS WRN KS THIS AFTERNOON/EVENING...STRONGEST ACTIVITY BEING
NEAR AND N OF FRONTAL ZONE...AND E OF FRONT RANGE/SANGRE DE CRISTOS.
PERSISTENT/LARGE SHIELD OF CONVECTION OCCURRING ATTM ACROSS NERN CO
MAY RESULT IN CONVECTIVE OVERTURNED/STABILIZED AIR MASS FOR MUCH OF
UPCOMING DAY...AND CASTS CONSIDERABLE UNCERTAINTY ON COVERAGE OVER
THAT AREA. HOWEVER...RESULTING MCV -- ALREADY EVIDENT IN
REFLECTIVITY ANIMATIONS JUST E DEN...MAY DRIFT SEWD TOWARD
RELATIVELY UNDISTURBED AIR MASS DURING AFTERNOON.
ALSO...DIFFERENTIAL HEATING/MOISTURE BOUNDARY SHOULD RESULT ACROSS
ERN CO...POTENTIALLY FOCUSING CONCENTRATION OF CONVECTION IN
ADDITION TO OROGRAPHIC ASCENT ZONES TYPICALLY ASSOCIATED WITH
MOIST/ELY BOUNDARY LAYER WINDS. BETWEEN THESE FOCI AND OUTFLOW
BOUNDARIES...LARGE COVERAGE OF CONVECTION INDICATES THAT...EVEN IF
VERY SMALL PERCENTAGE OF TSTMS PRODUCE STG-SVR HAIL OR GUSTS...AT
LEAST MRGL SVR PROBABILITIES ARE WARRANTED.
...AZ...
SCATTERED TSTMS MAY DEVELOP ACROSS THIS REGION DURING AFTERNOON
HOURS. ACTIVITY INITIALLY SHOULD FAVOR HIGHER TERRAIN...BUT SOME
TSTMS SHOULD MIGRATE OVER VALLEYS/DESERT AREAS LATE AFTERNOON. FCST
BUOYANCY APPEARS MRGL -- WITH WEAK MID-UPPER LAPSE RATES LIMITING
MLCAPES TO UNDER 1000 J/KG MOST AREAS. HOWEVER...DEEP/WELL-MIXED
SUBCLOUD LAYERS SHOULD SUPPORT POTENTIAL FOR STG/ISOLATED SVR
GUSTS...PARTICULARLY IF STORMS CAN CONCENTRATE SUFFICIENTLY TO
DEVELOP AMALGAMATED OUTFLOW.
...NWRN CONUS...
WIDELY SCATTERED TSTMS ARE EXPECTED TO FORM DURING AFTERNOON AS STG
HEATING CONTRIBUTES TO STEEPENING LOW-MIDLEVEL LAPSE RATES...IN
ENVIRONMENT OF FAVORABLE LOW LEVEL MOISTURE OVER CASCADES. STG SWLY
FLOW ALOFT AHEAD OF PACIFIC TROUGH SHOULD ENCOURAGE MOTION OF THIS
ACTIVITY ACROSS DRIER AND MORE WELL-MIXED AIR MASS FATHER E...WITH
POTENTIAL FOR ISOLATED GUSTS NEAR SVR LEVELS.
...NERN CONUS...
SCATTERED TSTMS ARE LIKELY ACROSS MUCH OF THIS REGION FROM LATE
MORNING INTO EARLY EVENING. WITH RELATIVELY COLD AIR ALOFT -- E.G.
500 MB TEMPS -14 TO -16 C -- ACTIVITY SHOULD BECOME STRONGEST AND
MOST CONCENTRATED OVER AREAS WHERE CLOUD BREAKS ALLOW MOST SUSTAINED
PRECONVECTIVE INSOLATION/HEATING. MID-UPPER LEVEL FLOW BECOMES MORE
DIFLUENT...BUT ALSO WEAKER...WITH NWD EXTENT ACROSS THIS
REGION...INDICATING POTENTIAL FOR GREATER CONCENTRATION OF
CLOUDS/PRECIP/CONVECTION TOWARD N BUT MORE POTENTIAL FOR SVR CLOSER
TO SRN NY...SRN NEW ENGLAND AND SWD THROUGH MID-ATLANTIC. SMALLER
AREA OF GREATER SVR PROBABILITIES MAY DEVELOP WITHIN BROAD 5-PERCENT
ZONE CURRENTLY OUTLOOKED...BUT MESOSCALE DEPENDENCY/UNCERTAINTY
PRECLUDES CATEGORICAL OUTLOOK ATTM.
..EDWARDS/JEWELL.. 08/07/2008
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