SWODY1
SPC AC 011218
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0718 AM CDT MON SEP 01 2008
VALID 011300Z - 021200Z
...THERE IS A SLGT RISK OF SVR TSTMS OVER THE CENTRAL GULF
COAST/LOWER MS RIVER VALLEY...
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PART OF THE NRN/CENTRAL
PLAINS...
...CENTRAL GULF COAST REGION...
HURRICANE GUSTAV CONTINUES TO MOVE ONSHORE JUST SOUTH OF NEW ORLEANS
AT DAY BREAK AND WILL LIKELY CONTINUE WNWWD INTO CENTRAL LA AND
WEAKEN GRADUALLY THROUGH THE DAY TODAY...REFERENCE LATEST FORECAST
FROM TPC. AN ACTIVE BAND OF THUNDERSTORMS HAS BEEN PERSISTENT TO THE
EAST-NORTHEAST OF GUSTAV/S CENTER IMPACTING THE FAR WRN FL PANHANDLE
INTO SRN AL...WITH LOW-TOPPED SUPERCELLS LIKELY TRAINING AS THEY
RACE NNWWD OFF THE GULF. SECONDARY BANDS WILL ALSO LIKELY EVOLVE
THROUGH THE DAY INTO MORE OF ERN LA/SRN MS WITH SIMILAR
SUPERCELL/TORNADO POTENTIAL.
AS IS TYPICAL FOR LAND FALLING HURRICANES...EXTREME LOW LEVEL
HELICITIES/SHEAR WILL REMAIN MAXIMIZED WITHIN NORTHEAST TO EAST
QUADRANT OF THE SYSTEM PLACING MUCH OF THE CENTRAL GULF COAST/LOWER
MS RIVER VALLEY UNDER AN INCREASED RISK OF A FEW TORNADOES THROUGH
THE PERIOD...ESPECIALLY DURING DAYLIGHT HOURS. IN ADDITION...WV
IMAGERY INDICATES DRIER AIR CONTINUING TO WRAP INTO THE ERN PORTION
OF GUSTAV AND MAY FURTHER ENHANCE THE TORNADO THREAT ACROSS THIS
REGION TODAY.
...ERN ND/NWRN MN SSWWD INTO SD/NEB...
12Z SURFACE ANALYSES INDICATE A COLD FRONT EXTENDING FROM NERN ND
SSWWD TO A LOW CENTER OVER WRN/CENTRAL SD...WHICH THEN BENDS MORE
WWD INTO CENTRAL WY. THIS FRONT WILL LIKELY ONLY PUSH SLOWLY EWD
FOR MUCH OF THE AFTERNOON AS THE LOW CENTER LIFTS INTO NERN ND...
WITH FRONT THEN ACCELERATING ESEWD THROUGH THE LATTER HALF OF THE
PERIOD. A RELATIVELY MOIST ENVIRONMENT REMAINS IN PLACE ACROSS THE
NRN/CENTRAL PLAINS AHEAD OF THIS SYSTEM...WHICH SHOULD CONTRIBUTE TO
MODEST DESTABILIZATION AS AIRMASS BECOMES QUITE WARM THIS AFTERNOON.
DESPITE WEAK MID LEVEL LAPSE RATES FORECAST OVER THE
REGION...FORECAST SOUNDINGS SUGGEST MLCAPE FROM 500-1500 J/KG WILL
DEVELOP. THIS WILL LIKELY BE SUFFICIENT FOR THUNDERSTORM
DEVELOPMENT NEAR THE FRONT DURING THE MID TO LATE AFTERNOON.
WHILE LACK OF STRONGER INSTABILITY WILL LIMIT STORM
INTENSITY...STRONG DEEP-LAYER WIND FIELD/SHEAR SHOULD SUPPORT MORE
ORGANIZED STORM-STRUCTURES...INCLUDING SUPERCELLS/LINES. SOMEWHAT
UNIDIRECTIONAL WIND PROFILES AND MOVEMENT PARALLEL OR SLIGHTLY TO
COOL SIDE OF SURFACE FRONT WOULD FAVOR PRIMARY THREAT OF DAMAGING
WINDS AND ISOLATED LARGE HAIL. HOWEVER...LOW LEVEL SHEAR IS
FORECAST TO BE QUITE STRONG UNDER 40-50 KT LLJ AND WARRANTS THE
POSSIBILITY OF A TORNADO OR TWO IF A DISCRETE STORM PERSISTS WITHIN
WARM SECTOR.
...NRN HIGH PLAINS INTO SNAKE RIVER VALLEY...
FRONT STALLING OVER NWRN NEB PANHANDLE/CENTRAL WY WILL MAINTAIN
RELATIVELY MOIST UPSLOPE FLOW ALONG AND NORTH OF THE BOUNDARY
TODAY...AHEAD OF STRONG MID/UPPER LEVEL SYSTEM MOVING OUT OF THE NRN
ROCKIES. INSTABILITY WILL REMAIN QUITE MARGINAL OVER THIS REGION
WITH LIMITED SURFACE HEATING. HOWEVER...VERY STRONG SHEAR SUGGESTS
THUNDERSTORMS INCREASING AHEAD OF APPROACHING SYSTEM/ASSOCIATED
SURFACE COLD FRONT MAY PRODUCE ISOLATED DAMAGING WINDS/LARGE HAIL AS
THEY ORGANIZE INTO SUPERCELLS AND CLUSTERS/LINES LATER TODAY AND
THIS EVENING OVER THE HIGH PLAINS OF ERN WY/WRN SD/WRN NEB.
FARTHER WEST...FORECAST SOUNDINGS SUPPORT WEAK INSTABILITY UNDER
POCKET OF VERY COLD /I.E. H5 TEMPS TO -22C/ MID LEVEL AIR...DESPITE
SEASONABLY COOL SURFACE CONDITIONS. THIS MAY SUPPORT A FEW
LOW-TOPPED THUNDERSTORMS WITH A RISK OF HAIL WITH THE STRONGER
STORMS. THREAT SHOULD DIMINISH OVERNIGHT AS AVAILABLE INSTABILITY
QUICKLY WANES.
..EVANS/CROSBIE.. 09/01/2008
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