SWODY1
SPC AC 301942
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0242 PM CDT SAT AUG 30 2008
VALID 302000Z - 311200Z
...THERE IS A SLGT RISK OF SVR TSTMS OVER THE FL KEYS...
...FL KEYS THROUGH TONIGHT...
18Z EYW SOUNDING AND VAD TRENDS SHOW LOW-LEVEL SHEAR STEADILY
INCREASING IN THE RIGHT FORWARD QUADRANT OF HURRICANE GUSTAV. NRN
MOST CONVECTIVE SPIRAL BAND IS ALREADY IMPACTING THE KEYS AND FL
STRAITS WITH RADAR VELOCITY DATA INDICATING SOME TRANSIENT SUPERCELL
STRUCTURES. PER LATEST NHC GUIDANCE...GUSTAV WILL CONTINUE NWWD
TONIGHT WITH THE KEYS REMAINING IN FAVORABLE RIGHT SEMICIRCLE OF
SYSTEM. THUS...THE SUPERCELL/TORNADO THREAT WILL LIKELY CONTINUE
WITH NERN/ERN MOST SPIRAL BAND. FOR ADDITIONAL NEAR TERM
GUIDANCE...SEE MCD 2188.
...MT/ND THROUGH TONIGHT...
SURFACE COLD FRONT FROM NERN MT SWWD INTO SWRN ID WILL CONTINUE TO
SLOWLY SHIFT SEWD THIS AFTERNOON AND TONIGHT IN ADVANCE OF
AMPLIFYING MIDLEVEL TROUGH OVER WRN CANADA INTO THE PACIFIC NW.
CONSIDERABLE HEATING AND SOME MOISTENING IS OCCURRING IN BOUNDARY
LAYER INVOF LEE TROUGH OVER THE WRN DAKOTAS. HOWEVER...A RATHER
WARM EML /PER 12Z SOUNDINGS/ IS LIMITING CONVECTIVE INSTABILITY A
NOTABLE CAP STILL REMAINING. AS SUCH...THERE IS SOME QUESTION AS TO
WHETHER STORM INITIATION WILL OCCUR OVER THE WRN DAKOTAS LATER THIS
AFTERNOON INTO TONIGHT.
IT APPEARS THAT THE BETTER POTENTIAL FOR STORM DEVELOPMENT IS ALONG
COLD FRONT OR IN IMMEDIATE POST-FRONTAL AIR MASS OVER MT...IN CLOSER
PROXIMITY TO HEIGHT FALLS/DYNAMIC FORCING FOR ASCENT ASSOCIATED WITH
EVOLVING UPPER TROUGH. AIR MASS IS RELATIVELY DRY WITH PW VALUES OF
GENERALLY LESS THAN 0.5-0.7 INCH. BUT...THE PRESENCE OF STEEP LAPSE
RATES AND THE NEWD ADVECTION OF MIDLEVEL MOISTURE PLUME MAY YIELD
SUFFICIENT CONVECTIVE INSTABILITY TO SUPPORT SCATTERED TSTM
DEVELOPMENT LATER TONIGHT. AS UPPER TROUGH SHIFTS EWD...VERTICAL
SHEAR WILL STRENGTHEN WITH TIME ALONG FRONTAL ZONE WITH ENVIRONMENT
BECOMING FAVORABLE FOR A FEW ORGANIZED STORMS CAPABLE OF DAMAGING
WINDS AND HAIL.
...LOWER CO VALLEY THROUGH THIS EVENING...
SUBSEQUENT NOCTURNAL TSTM EVENTS HAVE OVERTURNED AIR MASS
SUFFICIENTLY SUCH THAT CURRENT OBJECTIVE FIELDS AND 12Z SOUNDINGS
INDICATE A MORE STABLE AIR MASS THAN THE PREVIOUS COUPLE OF DAYS.
NONETHELESS...BOUNDARY LAYER DEWPOINTS IN THE 60S COMBINED WITH
TEMPERATURES IN THE 80S TO LOWER/MID 90S ARE RESULTING IN POCKETS OF
MODERATE INSTABILITY. WHILE VERTICAL SHEAR HAS ALSO DECREASED
SLIGHTLY TODAY...ENVIRONMENT WILL STILL REMAIN FAVORABLE FOR SOME
ORGANIZATION OF STORM CLUSTERS WITH THE THREAT FOR GUSTY WINDS AND
PERHAPS SOME HAIL.
...CNTRL HIGH PLAINS INTO LOWER MS VALLEY INTO THIS EVENING...
VISIBLE SATELLITE AND LIGHTNING DATA INDICATE TSTMS INCREASING IN
COVERAGE THIS AFTERNOON ALONG LOW-LEVEL CONFLUENCE ZONE FROM S-CNTRL
KS INTO ERN OK/NERN AR. AMBIENT AIR MASS IS HOT AND MOIST WITH
MLCAPES OF 2000-2500 J/KG. VERTICAL SHEAR REMAINS QUITE WEAK OWING
TO PROXIMITY OF UPPER HIGH. STILL...LOCALLY STRONG WIND GUSTS AND
SOME HAIL WILL BE POSSIBLE WITH THE MORE INTENSE PULSE-TYPE STORMS
THAT DEVELOP.
...SE ATLANTIC COAST INTO THIS EVENING...
A WEAK NE-SW ORIENTED SURFACE TROUGH AND SEA BREEZE BOUNDARIES HAVE
BEEN THE FOCUS FOR SCATTERED TSTM DEVELOPMENT THIS AFTERNOON WITHIN
A MOIST...UNSTABLE AIR MASS WITH MLCAPES OF 1500-2500 J/KG. HERE
TOO...VERTICAL SHEAR IS WEAK...THOUGH STRONG WIND GUSTS WILL BE
POSSIBLE WITH ANY MORE ORGANIZED STORM CLUSTERS.
..MEAD.. 08/30/2008
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