SWODY1
SPC AC 301627
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1127 AM CDT SAT AUG 30 2008
VALID 301630Z - 311200Z
...NO SVR TSTM AREAS FORECAST...
...FL KEYS THIS AFTERNOON INTO TONIGHT...
HURRICANE GUSTAV CONTINUES TO INTENSIFY S OF WRN CUBA WHILE MOVING
GENERALLY TO THE NW. THE OUTER NERN CONVECTIVE BANDS AND
STRENGTHENING LOW-MID LEVEL FLOW WILL OVERSPREAD THE KEYS THROUGH
TONIGHT. THE MORE FAVORABLE AREA FOR SUPERCELLS/TORNADOES WILL
LIKELY BE CONFINED TO THE MAIN OUTER BAND THAT NOW EXTENDS FROM
CENTRAL CUBA INTO THE FL STRAITS...WHILE EXTRAPOLATION OF RECENT
STORM MOTION AND THE OFFICIAL NHC FORECAST TRACK BOTH SUGGEST THAT
THIS MORE FAVORABLE CORRIDOR WILL JUST BRUSH THE LOWER KEYS LATER
TODAY INTO TONIGHT. STILL...THE FL KEYS AREA WILL BE MONITORED
CLOSELY...AND IT IS STILL POSSIBLE THAT A SLIGHT RISK UPGRADE COULD
BE NEEDED LATER THIS AFTERNOON OR EARLY TONIGHT.
...MT/ND AREA THROUGH TONIGHT...
LOW-LEVEL MOISTURE IS QUITE LIMITED THIS MORNING ACROSS CENTRAL AND
ERN MT WHERE BOUNDARY LAYER DEWPOINTS RANGE FROM THE MID 30S TO MID
40S...WHILE MID 50S DEWPOINTS ARE STILL LOCATED S NEAR AND S OF
I-90. SOME OF THIS LOW-LEVEL MOISTURE WILL SPREAD NWD TOWARD ND IN
RESPONSE TO LEE CYCLOGENESIS ACROSS SE MT AND INCREASING SLY FLOW
ACROSS THE PLAINS...BUT AN ELEVATED MIXED LAYER WILL LIKELY PROVIDE
SUBSTANTIAL CONVECTIVE INHIBITION ALONG THE SURFACE FRONT THAT WILL
MOVE INTO NW ND THIS EVENING. ISOLATED LARGE HAIL/DAMAGING WINDS
COULD OCCUR ACROSS N/NW ND THIS EVENING INTO EARLY TONIGHT IF STORMS
FORM ALONG THE BOUNDARY...BUT CONFIDENCE IN THUNDERSTORM DEVELOPMENT
IS RATHER LOW.
FARTHER W...MT WILL BE IMMEDIATELY DOWNSTREAM FROM A MID LEVEL
TROUGH THAT IS BEGINNING TO AMPLIFY OVER THE PAC NW. THIS MID LEVEL
TROUGH WILL BE ACCOMPANIED BY A COLD FRONT THIS AFTERNOON INTO
TONIGHT ACROSS WRN AND NRN MT. INSTABILITY WILL BE QUITE LIMITED
THROUGH THE PERIOD OVER MT...THOUGH SOME WEAK MID LEVEL INSTABILITY
MAY DEVELOP IN CONJUNCTION WITH THE STEEP LAPSE RATES AND THE NWD
SPREAD OF MID LEVEL MOISTURE FROM THE NRN FRINGES OF THE GREAT BASIN
MONSOONAL MOISTURE PLUME. THE INCREASING MID LEVEL FLOW AND STEEP
LAPSE RATES COULD SUPPORT A FEW STORMS WITH STRONG OUTFLOW
WINDS...DESPITE THE VERY MARGINAL INSTABILITY.
...SE ATLANTIC COASTAL PLAIN THIS AFTERNOON...
DAYTIME HEATING...A WEAK SURFACE TROUGH...AND THE SEA BREEZE WILL
ALL COMBINE TO SUPPORT SCATTERED THUNDERSTORMS THIS AFTERNOON FROM
SE GA TO SRN NC. A WEAK MID LEVEL TROUGH COINCIDES WITH THE
LOW-LEVEL BOUNDARIES AND THE CORRIDOR OF STRONGEST INSTABILITY.
MODIFIED 12Z SOUNDINGS SUPPORT MLCAPE NEAR 3000 J/KG THIS AFTERNOON
IN AN ENVIRONMENT OF RATHER WEAK VERTICAL SHEAR...THUS A FEW STORMS
MAY PRODUCE ISOLATED DAMAGING MICROBURSTS AND PERHAPS MARGINALLY
SEVERE HAIL.
...CENTRAL AND WRN AZ THIS AFTERNOON/EVENING...
DEBRIS CLOUDS FROM OVERNIGHT AND ONGOING STORMS WILL SLOW DAYTIME
HEATING/DESTABILIZATION OVER EXTREME WRN AZ/SE CA/SE NV.
HOWEVER...STRONGER SURFACE HEATING WILL OCCUR FARTHER E INTO CENTRAL
AZ...WHERE MODIFIED 12Z SOUNDINGS SUPPORT MODERATE INSTABILITY AGAIN
THIS AFTERNOON. HOWEVER...THE PRONOUNCED ELY MID LEVEL FLOW OF THE
PAST FEW DAYS HAS ALREADY WEAKENED SOME SINCE YESTERDAY...AND THE
FLOW SHOULD BECOME MORE SLY AND CONTINUE WEAKENING LATER TODAY INTO
TONIGHT. THUS...THE FLOW REGIME WILL BE LESS FAVORABLE FOR
CONVECTIVE CLUSTERS TO MOVE OFF THE HIGH TERRAIN INTO THE LOWER
DESERTS...THOUGH ISOLATED DOWNBURSTS WILL STILL BE POSSIBLE ACROSS
WRN AZ WHERE INSTABILITY WILL BE GREATEST THIS AFTERNOON/EVENING.
...KS/OK/AR THIS AFTERNOON...
A DIFFUSE BAROCLINIC ZONE EXTENDS FROM CENTRAL KS ACROSS NE OK INTO
CENTRAL AR. THERMODYNAMIC PROFILES ARE SIMILAR TO YESTERDAY ACROSS
THIS AREA...WHILE MID LEVEL FLOW WILL BECOME WEAK SELY AS OPPOSED TO
NELY YESTERDAY. THE NET RESULT SHOULD BE A FEW PULSE-TYPE STORMS
CAPABLE OF PRODUCING ISOLATED MICROBURSTS AND PERHAPS MARGINALLY
SEVERE HAIL.
..THOMPSON/GRAMS.. 08/30/2008
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