SWODY2
SPC AC 301721
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1221 PM CDT TUE JUN 30 2009
VALID 011200Z - 021200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM ERN NY/EXTREME WRN NEW
ENGLAND INTO NJ...
...THERE IS A SLGT RISK OF SVR TSTMS OVER THE CENTRAL/ERN NC AREA...
...THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF THE NRN/CENTRAL
PLAINS...
...SYNOPSIS...
UPPER LOW OVER THE GREAT LAKES IS FORECAST TO MOVE LITTLE THROUGH
TOMORROW AS A SERIES OF SHORT WAVE TROUGHS ROTATE AROUND THE
CYCLONIC CIRCULATION. THE UPPER RIDGE OVER THE NRN PLAINS IS
EXPECTED TO WEAKEN AS A SHORT WAVE TROUGH NOW MOVING ACROSS BC AND
THE FAR NRN INTERMOUNTAIN REGION MOVES ACROSS THE CANADIAN PRAIRIES.
FARTHER SOUTH...MODEL GUIDANCE IS IN GOOD AGREEMENT THAT A SHORT
WAVE TROUGH CURRENTLY MOVING NWD AROUND THE WRN PERIPHERY OF THE SRN
PLATEAU UPPER RIDGE WILL TURN EWD ACROSS WY TOMORROW REACHING THE
NRN PLAINS TOMORROW NIGHT.
AT THE SURFACE...OCCLUDED LOW NEAR THE LOWER GREAT LAKES WILL
GRADUALLY WEAKEN. A WEAK FRONT/CONVERGENCE ZONE EXTENDING SSEWD INTO
THE MID ATLANTIC STATES THEN SSWWD INTO THE SRN APPALACHIANS WILL
MOVE EWD ACROSS THE MID ATLANTIC REGION AND CAROLINAS. OVER THE
PLAINS REGION...A LOW OVER NRN WY WILL MOVE EWD/SEWD INTO THE NEB
PANHANDLE REGION DURING THE DAY...THEN DEVELOP SEWD INTO THE CENTRAL
HIGH PLAINS AT NIGHT. A COLD FRONT NORTH OF THE WY LOW IS FORECAST
TO MOVE EWD ACROSS MT AND THE HIGH PLAINS...WITH A WARM FRONT
EXTENDING SSEWD FROM THE LOW INTO THE SRN PLAINS.
...NJ NWD INTO ERN NY/EXTREME WRN NEW ENGLAND...
STRONG CONVECTION IS LIKELY TO DEVELOP AGAIN TOMORROW IN ADVANCE OF
THE UPPER LOW OVER THE LOWER GREAT LAKES REGION. GFS SURFACE
PATTERN IS FOLLOWED MORE CLOSELY OVER THIS AREA WITH A NNW/SSE
CONVERGENCE ZONE ACROSS ERN NY INTO NJ. SURFACE DEW POINTS ARE
EXPECTED TO REMAIN IN THE UPPER 50S/LOWER 60S...AND AN AXIS OF
MAXIMUM INSTABILITY IS FORECAST TO DEVELOP ALONG THE CONVERGENCE
ZONE. ALTHOUGH COVERAGE OF CONVECTION WILL BE MODULATED BY CLOUD
COVER AND LOCATIONS OF ENHANCED DIURNAL HEATING...RELATIVELY COOL
MID-LEVEL TEMPERATURES AND LARGE SCALE ASCENT AHEAD OF THE LOW WILL
AID IN DEVELOPMENT OF THUNDERSTORMS. STRONGER CELLS WILL BE CAPABLE
OF PRODUCING LARGE HAIL AND DAMAGING WIND GUSTS MAINLY DURING THE
AFTERNOON AND EARLY EVENING.
...CENTRAL/ERN NC AREA...
SEVERE RISK IS CONDITIONAL UPON THE INITIATION AND MAINTENANCE OF
ISOLATED/WIDELY SCATTERED THUNDERSTORMS. MODEL GUIDANCE HAS
PROVIDED MIXED SIGNALS CONCERNING THE FORMATION OF CONVECTION...WITH
12Z NAM AND A NUMBER OF SREF MEMBERS INDICATING DEVELOPMENT OF
PRECIPITATION DURING THE AFTERNOON IN ADVANCE OF THE COLD FRONT. IF
LOW LEVEL MOISTURE IS ABLE TO INCREASE AHEAD OF THE FRONT TO AROUND
60F...FORECAST SOUNDINGS INDICATE SUFFICIENT INSTABILITY AND MINIMAL
CAP TO SUPPORT A FEW THUNDERSTORMS. THE REGION WILL BE WITHIN A
BAND OF 35-40 KT WESTERLY MID LEVEL FLOW ON THE SOUTH SIDE OF THE
UPPER LOW...WITH SUFFICIENT VERTICAL SHEAR TO PROMOTE STORM
ORGANIZATION WITH ANY SUSTAINED UPDRAFTS THAT DEVELOP. STRONG
DIURNAL HEATING WILL STEEPEN LOW LEVEL LAPSE RATES AND ENHANCE
POTENTIAL FOR DAMAGING WIND GUSTS WITH STRONGER STORMS.
...PARTS OF THE NRN/CENTRAL PLAINS...
A LOW LEVEL MOISTURE AXIS WITH SURFACE DEW POINTS IN THE 60S IS
FORECAST TO PERSIST FROM THE NRN HIGH PLAINS SWD INTO THE CENTRAL
PLAINS NEAR THE AFOREMENTIONED SURFACE FRONT. THE ERN EDGE OF THE
REGION OF STEEP MID LEVEL LAPSE RATES WILL EXTEND INTO THE
PLAINS...AND WITH STRONG HEATING LIKELY TO OCCUR DURING THE
DAY...THE ENVIRONMENT WILL BECOME MODERATELY UNSTABLE WITH MLCAPE OF
1500-2500 J/KG.
THUNDERSTORM ARE EXPECTED TO DEVELOP BY MID/LATE AFTERNOON OVER
PARTS OF THE NRN HIGH PLAINS AS THE CAP WEAKENS AND DYNAMIC FORCING
PROVIDED BY THE SHORT WAVE TROUGH INCREASES ACROSS THE AREA. DEEP
LAYER SHEAR OF 35-45 KT WILL ENHANCE STORM ORGANIZATION AND
INTENSITY AND PROMOTE DEVELOPMENT OF A FEW SUPERCELLS...WITH PRIMARY
THREATS FOR LARGE HAIL AND DAMAGING WINDS. STORMS ARE LIKELY TO
GROW UPSCALE INTO A SEWD MOVING MCS DURING THE EVENING AS THE
NOCTURNAL LOW LEVEL JET STRENGTHENS OVER THE CENTRAL HIGH PLAINS
AFTER SUNSET. THE CONVECTION IS EXPECTED TO TRACK INTO PARTS OF NEB
AND POSSIBLY EXTREME NRN KS BY THE END OF THE PERIOD WITH A
CONTINUED THREAT FOR DAMAGING WINDS AND HAIL DURING THE OVERNIGHT
HOURS.
..WEISS.. 06/30/2009
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