Severe Thunderstorm Warning 133, NWS Raleigh, NC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
625 PM EDT THU JUN 11 2009

.SYNOPSIS...
A MOIST AND UNSTABLE AIR MASS...COUPLED WITH A SERIES OF UPPER LEVEL
DISTURBANCES...WILL CAUSE GOOD CHANCES OF SHOWERS AND STORMS TO
CONTINUE IN THE FORECAST THROUGH FRIDAY. A WEAK COLD FRONT WILL PUSH
SOUTH INTO THE REGION FRIDAY AND FRIDAY NIGHT... LIKELY STALLING
NEAR THE SOUTH CAROLINA BORDER FOR THE WEEKEND.
&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 625 PM THURSDAY...

MCV WAS PUSHING NE OVER SW VIRGINIA WITH TWO CONVECTIVE LINES
PUSHING EAST THROUGH WESTERN NC INTO CENTRAL SC. GSP RECORDED AT
WIND GUST TO 76 MPH ONE OF THE LINES EARLIER. ANOTHER SEVERE
THUNDERSTORM WATCH WILL BE ISSUED EAST OF THE CURRENT ONE. THIS WILL
COVER THE REST OF OUR REGION THROUGH 1200 AM.

THE STRONGEST INSTABILITY CONTINUED FROM RALEIGH AND ROCKY MOUNT
SOUTHWARD AS OF 625 PM. THUS... ISOLATED SEVERE STORMS COULD
GENERATE OUT AHEAD OF THE CONVECTIVE LINES APPROACHING FROM THE
WEST.
&&

.SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/...
AS OF 250 PM THURSDAY...

ALTHOUGH THE COLD FRONT IS FORECAST BY BOTH THE GFS AND THE NAM TO
MAKE PROGRESS SOUTH...INSTABILITY PARTICULARLY ON THE NAM IS
HAMPERED BY MID-LEVEL WARMING BETWEEN 500MB AND 600MB ON BUFR
SOUNDINGS. THIS REDUCES OVERALL INSTABILITY AND CAPE ON THAT MODEL
VERSUS THE GFS...WHICH CONTINUES TO BE MORE ROBUST WITH
INSTABILITY...FORECASTING LIFTED INDICES TO -5C AND MLCAPE EAST OF
U.S. 1 TO 2500J/KG. THE NAM ALSO FORECASTS DEEPER WESTERLY MID-
LEVEL WINDS...AND THE GFS FORECASTS SIMILAR WINDS ALBEIT A TRIFLE
MORE SOUTHWEST OVERALL. IN ADDITION...THE NAM FORECASTS MEAGER QPF...
BUT CANNOT DISCOUNT THE PROXIMITY OF THE FRONT AND A LINGERING
SURFACE TROUGH. TAKING THE CONSENSUS APPROACH...EXPECTING MORE
ISOLATED-TO-SCATTERED THUNDERSTORMS WITH THE BETTER COVERAGE NEAR
AND EAST OF U.S. 1 WHERE THERE IS HIGHER INSTABILITY AND SLIGHTLY
GREATER SURFACE CONVERGENCE. PROVIDED ALL OVERNIGHT COMPLEXES ARE
TO THE NORTH AND EAST...THICKNESSES SUPPORT MOS GUIDANCE HIGHS
AROUND 90.

FRIDAY NIGHT...FRONT CONTINUES TO MOVE SLOWLY SOUTH. BUFR
SOUNDINGS INCREASE STABILITY DIURNALLY AND PROVIDE FOR INCREASING
UPPER-LEVEL DIVERGENCE. WILL DIMINISH ANY CHANCES FOR SHOWERS AND
THUNDERSTORMS GRADUALLY NORTHWEST TO SOUTHEAST...MAINTAINING
SLIGHT CHANCES FOR SHOWERS AND THUNDERSTORMS THROUGH THE OVERNIGHT
HOURS IN THE SOUTHERN TIER OR TWO OF COUNTIES WHERE BOTH THE NAM
AND GFS CONTINUE SOMEWHAT DEEPER MOISTURE ON THETA-E SURFACES.
WHILE THERE COULD BE PATCHY FOG LATE IF SKIES CAN CLEAR IN
VICINITY OF THE FRONT WHERE DEW POINTS WILL BE GREATEST...
ESPECIALLY SOUTH AND EAST...WILL HOLD OFF ON THE MENTION FOR NOW.
OVERNIGHT LOWS SHOULD BE IN THE MID 60S TO AROUND 70.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
AS OF 250 PM THURSDAY...

THROUGH TUESDAY...
A WEAK FRONT SAGGING SOUTH WILL BE LINGERING SOMEWHERE ALONG THE
SOUTHERN TIER OF THE STATE THROUGH THE WEEKEND. IN THE MEANTIME...
THE UPPER FLOW WILL REMAIN PREDOMINANTLY FROM THE WEST. WITH NO
SIGNIFICANT AIRMASS CHANGE...HIGHS WILL BE CLIMBING WELL INTO THE
80S EACH DAY. THUS...CONVECTION IS EXPECTED TO BE MAINLY SCATTERED
AND LARGELY DIURNALLY DRIVEN WITH THE SURFACE FRONT PROVIDING A
MEASURE OF LOW LEVEL LIFT TO ENHANCE COVERAGE IN THE SOUTH. THE
SMALLER SCALE PERTURBATIONS FROM UPSTREAM SHORTWAVES OR MCS REMNANTS
WHICH WILL DOUBTLESS BE SWEPT ALONG IN THE UPPER WESTERLY FLOW ARE
NOT GOING TO BE CAPTURED OR INITIATED IN THE EXTENDED FORECAST
RANGE...THUS ADDING AN ADDITIONAL MEASURE OF UNCERTAINTY TO DAILY
COVERAGE. WILL CONTINUE ONGOING POPS IN THE 30-40 PERCENT RANGE
DURING THE AFTERNOONS WITH LESSER CHANCES OVERNIGHT.

TUESDAY THROUGH THURSDAY...
MID-UPPER FLOW BECOMES NORTHWEST AS UPPER RIDGING BUILDS NORTH INTO
THE UPPER MIDWEST...WHICH IN TURN NUDGES THE SURFACE FRONT SOUTH OF
THE AREA ON TUESDAY. THIS WILL RESULT IN SLIGHTLY COOLER AND MAINLY
DRY WEATHER FOR TUE AND WED...WITH SEASONABLE HIGHS AROUND 85. WILL
CONTINUE THE DRY TREND INTO THURSDAY AS HIGH PRESSURE OFFSHORE IS
FORECAST TO LINGER ACROSS THE AREA.

&&

.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
AS OF 155 PM THURSDAY...

VFR CONDITIONS ARE EXPECTED THROUGH MUCH OF THE REST OF THE
AFTERNOON AND OVERNIGHT HOURS...OUTSIDE OF AREAS OF SHOWERS AND
THUNDERSTORMS THAT MAY OCCUR AS A CONVECTIVE SYSTEM MOVES ALONG THE
NORTH CAROLINA/VIRGINIA BORDER...AND ALONG AND AHEAD OF A STRONG
UPPER-LEVEL DISTURBANCE MOVING EAST FROM TENNESSEE. IF THE MCV
CONTINUES WITH ITS PRESENT STRENGTH MOVING ACROSS CENTRAL NORTH
CAROLINA OVERNIGHT...THERE COULD BE A PERIOD OF GUSTY SURFACE WINDS
MAINLY FROM THE SOUTH. 925MB WINDS INCREASE TO AROUND 25KT
ESPECIALLY TOWARD KFAY AND KRWI LATE TONIGHT...AND WHILE THE WINDS
DO NOT APPEAR TO RISE TO LLWS CRITERIA...IN THE CONTINUING MOISTURE
AND WITH A BETTER INVERSION THERE ON BUFR SOUNDINGS...AREAS OF LOW
CLOUDS ARE LIKELY WITH LESSER CHANCES OF THIS TO THE WEST.

MIXING DURING THE MORNING SHOULD ALLOW FOR ANY LOW CLOUDS TO LIFT
WITH A SOUTHWEST-TO-WEST SURFACE FLOW DEVELOPING AHEAD OF A COLD
FRONT MOVING SOUTH TOWARD THE STATE. THERE WILL BE A CHANCE OF
THUNDERSTORMS FRIDAY AFTERNOON WITH THE BETTER CHANCE EAST AND
SOUTHEAST OF THE TRIAD WHERE THE INSTABILITY IS GREATER. DEEPER
WESTERLY FLOW MAY RESULT IN MORE ISOLATED-TO-SCATTERED COVERAGE OF
SHOWERS AND THUNDERSTORMS.

FRONT MOVES THROUGH MAINLY FRIDAY NIGHT...LINGERING ALONG THE SOUTH
CAROLINA BORDER WHILE WEAKENING. WEAK SURFACE WAVES ALONG THE FRONT
WITH MOISTURE REMAINING SHOULD CONTINUE TO PROVIDE FOR MAINLY
DIURNAL CHANCES FOR SHOWERS AND THUNDERSTORMS...AND THE POTENTIAL
FOR LATE NIGHT AND EARLY MORNING IFR CONDITIONS. FARTHER OUT IN
TIME...IT IS POSSIBLE BY TUESDAY A RIDGE BUILDING INTO CENTRAL NORTH
CAROLINA BEHIND ANOTHER FRONT USHERS IN MORE STABLE AND DRIER AIR.

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

SYNOPSIS...DJF/PWB
NEAR TERM...DJF/PWB
SHORT TERM...DJF
LONG TERM...MLM
AVIATION...DJF

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