SWODY1
SPC AC 061955
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0255 PM CDT WED JUN 06 2007
VALID 062000Z - 071200Z
..THERE IS A MDT RISK OF SVR TSTMS ACROSS MUCH OF THE
DAKOTAS...NORTHEAST NEB AND WRN MN...
..THERE IS A SLGT RISK OF SVR TSTMS FROM WY/MT EWD INTO THE CENTRAL
AND NRN PLAINS TOWARD THE UPPER MS RIVER VALLEY...
..THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF FL...
..SYNOPSIS...
DEEP UPPER LOW OVER EXTREME SERN ID WILL SHIFT EWD INTO SD TONIGHT
..AS A STRONG SHORTWAVE TROUGH/SPEED MAX LIFTS NEWD FROM SRN UT
INTO NEB. THIS RESULTS IN SURFACE LOW...CURRENTLY LOCATED NEAR THE
NEB/WY BORDER...TO DEEPEN AND LIFT NEWD ACROSS SD.
..NRN ROCKIES/PLAINS...
NUMEROUS THUNDERSTORMS HAVE DEVELOPED IN STRONG DIFFLUENT FLOW ALOFT
ACROSS PORTIONS OF WY/MT. MODERATE INSTABILITY COMBINED WITH DEEP
LAYER SHEAR AT 40 TO 50 KT AND FAVORABLE LOW LEVEL HODOGRAPHS WILL
SUPPORT SUPERCELLS WITH LARGE HAIL AND ISOLATED TORNADOES.
REFERENCE WW 352.
AS SURFACE LOW PULLS NEWD OUT OF THE ROCKIES...ALONG WITH THE STRONG
LARGE SCALE FORCING...SEVERE THUNDERSTORMS EXPECTED TO
DEVELOP/SPREAD ENEWD ACROSS PORTIONS OF ND/SD AND NEB. DESPITE
SLOWER MOISTURE RETURN THAN FORECAST BY MODELS...PER SURFACE
ANALYSIS AND LBF/UNR 18Z SOUNDINGS...STEEP LAPSE RATES AND SURFACE
DEWPOINTS NEAR 60F WILL RESULT IN MODERATE INSTABILITY. THIS
INSTABILITY ALONG WITH 40-50 KT DEEP LAYER SHEAR WILL SUPPORT
SUPERCELLS. INITIAL STORMS MAY BE CELLULAR IN NATURE WITH A FEW
TORNADOES POSSIBLE...THOUGH RELATIVELY DRY BOUNDARY LAYER SUGGESTS
THAT SEVERE HAIL AND WIND SHOULD BE THE MAIN THREAT. THE GREATEST
TORNADO POTENTIAL IS FORECAST ACROSS NWRN NEB AND WRN/CENTRAL
SD...WHERE THE LOW LEVEL WINDS WILL BE BACKED IN ADVANCE OF
ISALLOBARIC COUPLET/SURFACE LOW.
THIS EVENING...DRY AIR ALOFT AND STRONG DOWNDRAFTS ARE LIKELY TO
RESULT IN STORMS CONGEALING INTO A LINE AND THEN MOVING RAPIDLY
ENEWD WITH WIND DAMAGE THE MAIN THREAT. THE STRENGTH OF THE UPPER
FORCING...WIND PROFILES AND STRENGTHENING LOW LEVEL JET SUPPORT A
POSSIBLE DERECHO TYPE EVENT AS THE SYSTEM RACES NEWD ACROSS THE
DAKOTAS AND INTO WRN MN OVERNIGHT.
..CENTRAL PLAINS...
STRONG CAPPING AND EXTENSIVE HIGH CLOUDS ARE EXPECTED TO INHIBIT
CONVECTIVE DEVELOPMENT THROUGH MOST OF THE AFTERNOON. HOWEVER...
APPROACHING 70-80 KT MID LEVEL JET ACCOMPANIED BY SYNOPTIC SCALE
ASCENT MAY BE SUFFICIENT FOR A FEW STORMS TO DEVELOP ACROSS WRN
KS/SWRN NEB. WHILE THE AIR MASS AND SHEAR WILL BE VERY FAVORABLE FOR
SUPERCELLS...UNCERTAINTY STILL EXISTS HOW MANY...IF ANY... STORMS
WILL DEVELOP SINCE THE STRONGER FORCING WILL BE NORTH OF NRN AND WRN
KS/SWRN NEB.
..SERN U.S...
VERY MOIST AND UNSTABLE ENVIRONMENT IS RESULTING IN NUMEROUS STORMS
ACROSS FL AND THE NERN GULF OF MEXICO COASTAL STATES. ALTHOUGH
SEVERE WEATHER HAS BEEN SLOW TO DEVELOP...APPROACHING SHORTWAVE
TROUGH MOVING THROUGH THE NRN GULF AND MODERATE INSTABILITY MAY
SUPPORT A FEW STRONG TO SEVERE ORGANIZED CLUSTERS/STORMS...WITH
MARGINALLY SEVERE HAIL/WIND.
.IMY.. 06/06/2007
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