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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KRAH 220641
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
241 AM EDT WED MAY 22 2013

.SYNOPSIS...
-- Changed Discussion --
BERMUDA HIGH PRESSURE WILL EXTEND INTO THE MIDDLE ATLANTIC TODAY. A
SURFACE PRESSURE TROUGH WILL DEVELOP IN THE LEE OF THE APPALACHIANS
THURSDAY...FOLLOWED BY THE PASSAGE OF A COLD FRONT THURSDAY NIGHT.
-- End Changed Discussion --

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 945 PM TUESDAY...

THE PESKY WEAK MID-LEVEL IMPULSE THAT HAS TAKEN 3 DAYS TO CROSS THE
STATE AND LARGELY RESPONSIBLE FOR THE UNSETTLED/STORMY WEATHER
DURING THE SAME TIME...IS FINALLY IN THE PROCESS OF PUSHING OUT TO
SEA. THIS WILL SPELL FOR DRIER CONDITIONS TONIGHT THAN THAT OF THE
PAST FEW NIGHTS. WITH THAT SAID...THE NORTHERN/NORTHWESTERN PIEDMONT
COULD STILL SEE SOME ISOLATED CONVECTION OVER THE NEXT COUPLE OF
HOURS AS BAND OF COLD POOL DRIVEN CONVECTION CROSSES THE MOUNTAINS
AND MOVES NORTHEAST INTO THE VIRGINIAS.

WITH THE PLUME OF HIGH 1.5-1.7" PWAT STILL IN PLACE OVER THE
REGION...LOW CEILINGS AND FOG ARE APT TO DEVELOP AFTER MIDNIGHT.
LOWS TONIGHT IN THE MIDDLE TO UPPER 60S.

&&

.SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/...
AS OF 218 PM TUESDAY...

ON WEDNESDAY CENTRAL NORTH CAROLINA WILL BE BETWEEN THE EXITING
SHORTWAVE SYSTEM THAT HAS BROUGHT US ALL OF THE RAIN OVER THE LAST
SEVERAL DAYS AND THE APPROACHING FRONTAL SYSTEM WITH THE PARENT LOW
PRESSURE SYSTEM CROSSING THE WESTERN GREAT LAKES. IT SHOULD BE THE
DRIEST DAY OF THE WEEK SO FAR BUT THERE WILL STILL BE PLENTY OF LOW
LEVEL MOISTURE CONVERGENCE BETWEEN RETURN FLOW FROM THE SURFACE HIGH
OFF OF THE ATLANTIC COAST AND SOUTHWESTERLY FLOW AHEAD OF THE
FRONTAL SYSTEM TO THE WEST. PRECIPITABLE WATERS WILL ONLY BE
SLIGHTLY LESS THAN TODAY ABOUT 1.6 INCHES OR SO IN THE EAST. SEVERE
PARAMETERS OUTSIDE OF INSTABILITY ARE ONCE AGAIN LACKING...VERY
SIMILAR TO THE ENVIRONMENT SEEN OVER THE LAST SEVERAL DAYS. A BIT
MORE RIDGING AND SUBSIDENCE IN THE MID TO UPPER LEVELS SHOULD KEEP
US A LITTLE DRIER THAN EARLIER IN THE WEEK BUT STILL EXPECT SOME
CONVECTIVE DEVELOPMENT BY LATE AFTERNOON. HEAVY RAIN WILL ONCE AGAIN
BE THE PRIMARY THREAT. WITH SOUTHERLY FLOW AND GREATER INSOLATION
ACROSS MUCH OF THE AREA...EXPECT HIGH TEMPERATURES AGAIN IN THE MID
80S OVER MUCH OF THE CWA. DEWPOINTS WILL REMAIN HIGH AGAIN ON
WEDNESDAY NIGHT KEEPING THE THREAT FOR LOW STRATUS AND FOG AROUND
FOR ONE MORE NIGHT AS LOWS APPROACH THE DEWPOINTS...MIDDLE TO UPPER
60S.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
AS OF 255 PM TUESDAY...

THURSDAY THROUGH FRIDAY...A COLD FRONT APPROACHES THURSDAY AND MOVES
THROUGH THURSDAY NIGHT INTO EARLY FRIDAY...FOLLOWED BY THE PRIMARY
PUSH OF COLDER AIR WITH A SECOND FRONT DURING THE DAY ON FRIDAY. ON
THURSDAY...THE RIGHT ENTRANCE REGION OF A 70KT 300MB JET GETS CLOSE
TO CENTRAL NORTH CAROLINA BUT MAINLY STAYS NORTH...WHILE 850MB LIFT
REMAINS MODEST AND 850MB THETA-E AND PRECIPITABLE WATER VALUES...
HIGHEST IN THIS PERIOD AT 1.5 INCHES AROUND 12Z THURSDAY...GRADUALLY
FALL AS FORECAST BY THE GFS THROUGH THURSDAY AND INTO FRIDAY. THOSE
PRECIPITABLE WATER VALUES FALL TO JUST BELOW AN INCH IN THE COASTAL
PLAIN AND BELOW 0.75 INCH IN THE TRIAD BY LATE FRIDAY AFTERNOON.
1000-500MB LAPSE RATES ARE MAXIMIZED ONLY TO AROUND 6.5C/KM AROUND
18Z THURSDAY...WITH AROUND 1000J/KG OF MIXED-LAYER CAPE MAINLY
TOWARD THE COASTAL PLAIN THURSDAY AFTERNOON.

850MB LIFT IS MODEST THURSDAY...AS IT APPEARS THE BEST INSTABILITY
IS OUT AHEAD OF THE BEST FORCING...WITH THE SURFACE BOUNDARY QUITE
POSSIBLY NOT MOVING INTO THE NORTHWEST PIEDMONT UNTIL VERY LATE IN
THE DAY THURSDAY. GFS BUFR SOUNDINGS...AND TO A SIMILAR DEGREE THE
NAM THOUGH THE NAM IS MORE MOIST...HAVE SLENDER CAPE AND CIN DOES
START TO INCREASE OVER A DEEP LAYER THURSDAY EVENING. MOS CHANCES
FOR SHOWERS AND THUNDERSTORMS ARE MOSTLY IN THE CHANCE RANGE
THURSDAY AND RIGHT NOW THAT SEEMS REASONABLE GIVEN WHAT CURRENTLY
APPEARS TO BE BETTER LOW-LEVEL FORCING LAGGING BETTER BOUNDARY LAYER
MOISTURE AND INSTABILITY. BUFR SOUNDINGS START TO STABILIZE THURSDAY
NIGHT AND WILL MAINTAIN A SLIGHT CHANCE OF SHOWERS OVERNIGHT TO
ACCOUNT FOR THE FIRST SURFACE FRONT...BUT IT IS POSSIBLE THAT BY THE
OVERNIGHT HOURS...PARTICULARLY ALONG AND WEST OF U.S. 1...ANY
REMAINING INSTABILITY IS SO MARGINAL IN A DRYING BOUNDARY LAYER THAT
EVEN AN ISOLATED SHOWER IS REMOTE. GIVEN THE MODEST SHEAR...MAINLY
LESS THAN 25KT 0-6KM THURSDAY AFTERNOON TOWARD INTERSTATE 95 AND
LESS TOWARD THE WEST...AND MODEST INSTABILITY WILL CONTINUE TO LEAVE
OUT THE MENTION OF SEVERE WEATHER CURRENTLY IN THE HWO. HIGHS IN THE
LOWER TO MID 80S THURSDAY CLOSER TO THE MAV MOS AND 1000-850MB
THICKNESSES...THE FORMER WHICH HAS HAD A GOOD TRACK RECORD LATELY
OVERALL COMPARED TO THE MET. OVERNIGHT LOWS THURSDAY NIGHT IN THE
UPPER 50S NORTHWEST TO THE MID 60S FAR SOUTHEAST.

FRIDAY...THE GFS HAS TRENDED TOWARD GREATER HEIGHT FALLS APPROACHING
CENTRAL NORTH CAROLINA LATE IN THE DAY. THE PRIMARY PUSH OF COLDER
AIR MOVES THROUGH DURING THE DAY BASED ON THE LATEST TIMING...AND
WHILE THERE IS AT LEAST MODEST LIFT WITH THE SURFACE BOUNDARY AND
THE HEIGHT FALLS...CURRENTLY GFS BUFR SOUNDINGS APPEAR CAPPED TO
DEEP CONVECTION. SOME OF THE GUIDANCE SUGGESTS A FEW SHOWERS IN THE
IMMEDIATE VICINITY OF INTERSTATE 95 MOVING EAST AND DEVELOPING
FURTHER TOWARD THE COAST IN MORE MOIST AIR AND ALONG THE BOUNDARY
DURING THE AFTERNOON...BUT BASED ON THE FORECAST CAP ALOFT AND DRIER
AIR MOVING ACROSS THE REGION AT THE SURFACE...WILL LEAVE OUT THE
MENTION OF SHOWERS FOR FRIDAY FOR THIS FORECAST. HIGHS FRIDAY IN THE
LOWER 70S FAR NORTHWEST...TO AROUND 80 SOUTHEAST. FRIDAY AFTERNOON
COULD END UP A LITTLE BREEZY BEHIND THE FRONTAL PASSAGE WITH
OCCASIONAL WIND GUSTS IN THE 20S KTS...POSSIBLY CLOSE TO 30MPH
BRIEFLY TOWARD THE TRIAD.

FRIDAY NIGHT THROUGH TUESDAY...A SECONDARY FRONT WILL BE MOVING
OFFSHORE LATE FRIDAY...WITH HIGH PRESSURE BUILDING INTO CENTRAL
NORTH CAROLINA FOR AT LEAST THE START OF THE WEEKEND. BASED ON THE
CONSENSUS OF THE LONG-TERM GUIDANCE...A WEAK SURFACE TROUGH OR COLD
FRONT MOVES TOWARD CENTRAL NORTH CAROLINA FROM THE NORTH LATE IN THE
WEEKEND. WITH THE BROAD SURFACE PATTERN MADE UP OF HIGH PRESSURE
FROM THE ATLANTIC INTO THE NORTHERN GULF...CONVERGENCE ALONG THE
FRONT IS EXPECTED TO BE WEAK. THE FLOW ALOFT SHOULD BE PREDOMINANTLY
NORTHWEST WITH PERIODIC SHORTWAVES IN THAT NORTHWEST FLOW. BOTH THE
GFS AND THE ECMWF SUGGEST THAT AN 850MB BOUNDARY MOVES SOUTH ACROSS
VIRGINIA AND IS LOCATED JUST NORTH OF THE STATE BY 12Z MONDAY. THIS
COULD HELP TO ENHANCE LOW-LEVEL CONVERGENCE SOMEWHAT...THOUGH GIVEN
THE RIDGING EXPECTED OVER THE GULF...VERY DEEP MOISTURE IS NOT
CURRENTLY ANTICIPATED.

MEAN RELATIVE HUMIDITY IS FORECAST TO INCREASE BY MONDAY...AND
COARSE MODEL SOUNDINGS ARE SUGGESTIVE OF AT LEAST AN INCREASE IN
CLOUDS BY THEN. SOME OF THE LONG-TERM GUIDANCE PRODUCES LIGHT QPF BY
MONDAY ESPECIALLY OVER NORTHERN PARTS OF THE STATE...CLOSER TO THE
850MB BOUNDARY THAT IS FORECAST BY MUCH OF THAT GUIDANCE. WITH
SURFACE AND 850MB RIDGING OVER THE GULF AND LIMITED SURFACE MOISTURE
RETURN...ANY RAINFALL THAT DEVELOPS IN MID-LEVEL LIFT NEAR WEAK
850MB AND SURFACE BOUNDARIES SHOULD BE LIGHT. FOR NOW...PLAN TO SHOW
AN INCREASE IN CLOUDS LATE IN THE HOLIDAY WEEKEND AND MAINTAIN THE
SLIGHT CHANCE OF SHOWERS MONDAY...CONTINUING THE SLIGHT CHANCE INTO
TUESDAY AS THE ORIENTATION OF ANY SURFACE BOUNDARY DOES NOT APPEAR
TO CHANGE MUCH FROM MONDAY INTO TUESDAY. MID-LEVEL HEIGHTS DO RISE
FROM MONDAY INTO TUESDAY...SO IN A RELATIVE SENSE THE CHANCES FOR
SHOWERS MAY END UP BEING A LITTLE HIGHER MONDAY COMPARED TO
TUESDAY...BUT GIVEN MANY MODEL RUNS BEFORE THE END OF NEXT WEEKEND
AND THE BROAD RIDGING IN PLACE OVER MUCH OF THE SOUTHEAST...WILL
MAINTAIN SIMPLY SLIGHT CHANCES FOR NOW. TEMPERATURES SHOULD AVERAGE
A CATEGORY OR TWO COOLER THAN NORMAL EARLY IN THIS PART OF THE
LONG-TERM PERIOD...CLOSER TO NORMAL TOWARD THE END OF THE PERIOD.

&&

.AVIATION /06Z WEDNESDAY THROUGH SATURDAY/...
-- Changed Discussion --
AS OF 240 AM WEDNESDAY...

A CONTINUED VERY MOIST AIR MASS WILL RESULT IN A HIGH CHANCE OF
LIFR-IFR CEILINGS THIS MORNING. THESE CEILINGS WILL LIFT AND SCATTER
TO VFR WITH HEATING THROUGH MIDDAY. HEATING OF THE MOIST AIR MASS
WILL ALSO CAUSE WIDELY SCATTERED SHOWERS AND STORMS TO DEVELOP THIS
AFTERNOON...BUT WITH LESSER COVERAGE VERSUS PREVIOUS DAYS OWING TO
THE WEAKENING AND DEPARTURE OF A LIFT-INDUCING TROUGH THAT RESIDED
OVER THE AREA DURING RECENT DAYS. UNTIL A COLD FRONT SWEEPS
ACROSS CENTRAL NC THU NIGHT...THE CONTINUED VERY MOIST REGIME WILL
PROMOTE ADDITIONAL LOW STRATUS DEVELOPMENT TONIGHT...AND A CONTIUED
THREAT OF MAINLY AFTERNOON SHOWERS AND STORMS. VFR CONDITIONS WILL
OTHERWISE PREVAIL IN CANADIAN HIGH PRESSURE THROUGH THE WEEKEND.
-- End Changed Discussion --

&&

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

&&

$$

SYNOPSIS...MWS
NEAR TERM...CBL
SHORT TERM...ELLIS
LONG TERM...DJF
AVIATION...MWS