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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KRAH 210716
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
300 AM EDT TUE MAY 21 2013

.SYNOPSIS...
A TROUGH OVER THE REGION WILL GRADUALLY WEAKEN THROUGH WEDNESDAY. A
STRONG COLD FRONT WILL APPROACH THE REGION FROM THE NORTHWEST LATE
THURSDAY... THEN PUSH THROUGH TO THE COAST BY FRIDAY MORNING. COOL
HIGH PRESSURE WILL FOLLOW THE FRONT LATE FRIDAY INTO THE WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 315 AM TUESDAY...

DELAYED A BIT WITH DISCUSSION TO SEE THE LATEST EC MODEL SINCE
MODELS WERE AT ODDS ON TIMING/LOCATION OF CONVECTION CHANCES TODAY.

WATER VAPOR SATELLITE DATA INDICATED THE WEAKENING MID/UPPER TROUGH
STILL LINGERING OVER THE REGION. PRECIPITABLE WATER VALUES REMAIN
VERY HIGH (GENERALLY 1.5 TO 1.75 INCHES). AT THE SURFACE... A WEAK
TROUGH WAS LOCATED OVER THE EASTERN PIEDMONT WITH DEW POINT VALUES
IN THE UPPER 60S TO NEAR 70. ONLY SCATTERED SHOWERS WERE NOTED OVER
THE COASTAL PLAIN AT 06Z/21 MAY.

THE LATEST HI-RES MODELS... IN PARTICULAR THE HRRR (WHICH PREFORMED
WELL WITH THE CONVECTION ON MONDAY)... BUT INCLUDING THE NMM EAST
AND ARW EAST INDICATE SOME DEVELOPMENT OF CONVECTION WESTWARD
BETWEEN 09Z AND 12Z OVER THE SOUTHERN PIEDMONT AND SANDHILLS
REGION.... SPREADING NE ACROSS THE FAYETTEVILLE AND RALEIGH AREAS
AROUND RUSH HOUR THIS MORNING. INTERESTINGLY ENOUGH... THESE HI-RES
MODELS ALSO INDICATE THE TROUGH AND ASSOCIATED CONVECTION SETTLING
SOUTH INTO THE LOWER COASTAL PLAIN BY THIS AFTERNOON. THIS IS IN
STARK CONTRAST TO THE OPERATIONAL NAM/GFS WHICH BOTH DEPICT AN
UPTICK IN CONVECTION WITH AFTERNOON HEATING... AND LITTLE THIS
MORNING.

IN ADDITION... THE HI-RES MODELS ALSO SHOW THE CURRENT LINE OF
STORMS OVER WESTERN KY/TN SURGING TOWARD THE APPALACHIANS LATER
TODAY... THEN POSSIBLY CROSSING THE MOUNTAINS INTO THE PIEDMONT
BETWEEN 00Z-06Z/WED (TONIGHT).

NEEDLESS TO SAY... CONVECTION LOCATION AND TIMING IS DIFFICULT AT
BEST TO FORECAST BEYOND 6 HOURS... THEREFORE WE WILL USE THE LATEST
SATELLITE/RADAR TRENDS... ALONG WITH CURRENT DATA TO TRY TO PIN DOWN
THE FAVORED TIMING/LOCATION OF CONVECTION TODAY AND TONIGHT.

FOR NOW... SINCE THE HRRR PREFORMED WELL MONDAY WITH THIS TROUGH
OVERHEAD... WE WILL LEAN TOWARD SCATTERED CONVECTION THIS MORNING...
WITH ADDITIONAL SCATTERED CONVECTION MAINLY SOUTH AND EAST THIS
AFTERNOON. MORE ISOLATED STORMS EXPECTED TO THE NORTH AND WEST.
HIGHS WILL RETURN TO NORMAL WITH ADDITIONAL HEATING TODAY... LOWER
TO MID 80S.

TONIGHT... AT LEAST SOME CHANCE OF A LINE OF STORMS COMING OUT OF
THE BLUE RIDGE APPROACHING OR AROUND SUNSET. THE AIR MASS SHOULD
BECOME MORE UNSTABLE ESPECIALLY OVER THE WESTERN PIEDMONT DURING
THIS TIME. HOWEVER... MLCAPES OF LESS THAN 1500 J/KG SHOULD YIELD
SUB SEVERE CONVECTION ALONG AND EAST OF THE BLUE RIDGE TODAY OR
TONIGHT. LOW END CHANCE OF SHOWERS/STORMS INTO THE MIDNIGHT HOUR IN
THE WEST... OTHERWISE PARTLY CLOUDY. LOWS IN THE MID TO UPPER 60S.

&&

.SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/...
AS OF 310 AM TUESDAY...

WEAK SHORTWAVE RIDGING OVER THE REGION WILL YIELD MOSTLY DRY AND
WARM WEATHER FOR ONE DAY (WED). HOWEVER...SUFFICIENT MOISTURE WILL
STILL BE IN PLACE OVER THE REGION...WITH PWAT VALUES HOVERING NEAR
1.5 INCHES OR SO. WIDELY SCATTERED AFTERNOON AND EVENING
THUNDERSTORMS CAN BE EXPECTED. HIGHS SHOULD BE IN THE MID/UPPER
80S... WITH OVERNIGHT LOWS IN THE MID/UPPER 60S.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
-- Changed Discussion --
AS OF 300 AM TUESDAY...

UPPER LEVEL TROUGH WILL MOVE EASTWARD FROM THE MIDWEST ON
THURSDAY...WHICH WILL PUT THE AREA IN DEEP SOUTH TO SOUTHWESTERLY
FLOW DURING THE DAY. WITH MOISTURE IN PLACE AND SUFFICIENT
INSTABILITY... WITH MLCAPE VALUES OF 500 TO 1000 J/KG...
THUNDERSTORMS WILL DEVELOP DURING THE DAY. BULK SHEAR VALUES NEAR 25
KTS WILL SUPPORT THE DEVELOPMENT OF SOME MULTICELL CLUSTERS... AND
FEW STRONGER STORMS WITH GUSTY WINDS ARE POSSIBLE. NO WIDESPREAD
SEVERE WEATHER IS EXPECTED... AS THE BEST UPPER LEVEL FORCING
REMAINS NORTH OF THE AREA. HIGHS IN THE LOW TO MID 80S... LOWS IN
THE MID 60S.

THE ASSOCIATED COLD FRONT WILL PROGRESS INTO WESTERN NORTH CAROLINA
THURSDAY EVENING... REACHING THE COAST BY ABOUT 12Z FRIDAY. MIDLEVEL
DRYING WILL SPREAD ACROSS THE AREA FRIDAY... ENDING PRECIPITATION
AND DECREASING CLOUD COVER THROUGH THE DAY FROM WEST TO EAST. COLD
ADVECTION WILL TEMPER HIGHS... WHICH WILL BE IN THE MID 70S TO LOW
80S. COOLER LOWS IN THE MID 50S.

THE TROUGH MOVES OFF THE COAST EARLY SATURDAY... WITH AN UPPER LEVEL
RIDGE ACROSS THE MIDDLE OF THE COUNTRY AND THE SURFACE HIGH
POSITIONED WEST OF THE AREA... PUTTING THE REGION IN A NORTHWEST
FLOW REGIME THROUGH THE WEEKEND... AND KEEPING TEMPERATURES
SEVERAL DEGREES BELOW NORMAL THROUGH MONDAY... WITH HIGHS IN THE
UPPER 70S TO NEAR 80.. AND LOWS IN THE MID TO UPPER 50S.
-- End Changed Discussion --

&&

.AVIATION /00Z TUESDAY THROUGH FRIDAY/...
AS OF 140 AM TUESDAY...

24 HOUR TAF PERIOD:

LIFR TO IFR CIGS AND MVFR VSBYS EXPECTED THROUGH 13Z-15Z TODAY...
THEN VFR CONDITIONS THIS AFTERNOON. ISOLATED TO SCATTERED
THUNDERSTORMS POSSIBLE THIS AFTERNOON. MVFR TO IFR CIGS AND VSBYS
MAY REDEVELOP LATER TONIGHT 09Z-12Z... FOLLOWED BY VFR CONDITIONS
WEDNESDAY.

LONG TERM:
AREAS OF STRATUS (LIFR TO IFR CIGS) AND VSBYS ARE EXPECTED AGAIN
THURSDAY MORNING. OTHERWISE... MOSTLY VFR CONDITIONS THU-FRI WITH A
CHANCE OF SHOWERS AND THUNDERSTORMS WITH MVFR CIGS/VSBYS BOTH DAYS.
&&

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

&&

$$

SYNOPSIS...PWB
NEAR TERM...BADGETT
SHORT TERM...BADGETT
LONG TERM...SEC
AVIATION...PWB