Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 052015 RRA
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
415 PM EDT TUE MAY 5 2015

.SYNOPSIS...BERMUDA HIGH PRESSURE WILL EXTEND INTO OUR REGION
THROUGH MID WEEK. AN AREA OF LOW PRESSURE WILL FORM NEAR THE BAHAMAS
AND MEANDER OFF THE SOUTHEAST COAST DURING THE MIDDLE OF THE WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 230 PM TUESDAY...

HIGH PRESSURE WILL CONTINUE TO RIDGE WESTWARD INTO CENTRAL NC...EVEN
AS THE HIGH SHIFTS OFFSHORE. SKIES WILL GENERALLY BE CLEAR...WITH
SOME INCREASING CLOUDS IN THE FAR SOUTHEAST TOWARD DAYBREAK
WEDNESDAY. EXPECT WINDS TO BECOME LIGHT AND VARIABLE OVERNIGHT. MILD
LOWS TONIGHT...MAINLY IN THE MID TO UPPER 50S.

&&

.SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/...
AS OF 240 PM TUESDAY...

A WEAK SURFACE TROUGH WILL STALL TO THE NORTH ON WEDNESDAY NIGHT...
WITH HIGH PRESSURE OVER THE NE U.S. AND OFF THE CAROLINA COAST. THE
BIGGER FEATURE WILL BE THE CLOSED LOW DEVELOPING OFF THE EAST
FLORIDA COAST...WHICH IS EXPECTED TO MOVE NORTH-NORTHEAST TOWARD THE
CAROLINAS THROUGH WEDNESDAY NIGHT. FOR NOW...IT APPEARS THAT THE
SYSTEM WILL STAY TO THE SOUTH THROUGH WEDNESDAY NIGHT...WITH THE
MAIN IMPACT OVER CENTRAL NC BEING INCREASING CLOUDINESS FROM THE SE
AND AN INCREASE IN AFT/EVE WINDS. THERE IS A SLIGHT CHANCE FOR SOME
SHOWERS/STORMS TO DEVELOP IN THE AFT/EVE ALONG THE STALLED BOUNDARY
TO THE NORTH...BUT EXPECT MOST OF THE ACTIVITY TO STAY TO THE NORTH
AND NORTHWEST OF CENTRAL NC. WITH LITTLE TO NO CHANGE IN AIRMASS...
AND BERMUDA HIGH PRESSURE CONTINUING TO RIDGE INTO THE AREA...
EXPECT HIGHS IN THE LOW TO MID 80S. WITH THE INCREASING CLOUDS
OVERNIGHT AND SOME WEAK WAA...LOWS WILL BE A FEW DEGREES WARMER THAN
PREVIOUS NIGHTS...MAINLY IN THE UPPER 50S.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
AS OF 415 PM TUESDAY...

THE MAIN FORECAST PROBLEM THROUGH THE PERIOD REMAINS THE EVOLUTION
OF AN AREA OF LOW PRESSURE...WITH POSSIBLE SUB-TROPICAL
CHARACTERISTICS...FORECAST TO FORM NEAR THE BAHAMAS AND DRIFT NEAR
THE SOUTHEAST US COAST THROUGH THE END OF THE WEEK. WHILE TWO MODEL
CAMPS REMAIN...WITH SOLUTIONS RANGING FROM THE NCEP ONES ON THE
WESTERN SIDE OF THE GUIDANCE ENVELOPE TO MORE EASTERN ONES DEPICTED
BY THE NON-NCEP MODELS...THE SPREAD HAS SIGNIFICANTLY DECREASED IN
THE PAST 24 HOURS. THE DECREASING MODEL SPREAD RESULTS FROM A
WESTWARD SHIFT IN THE NON-NCEP GUIDANCE...INCLUDING THE 12Z OP
ECMWF...WHICH YIELDS RELATIVE INCREASED FORECAST CONFIDENCE IN A
CLOSER TO THE CAROLINAS COAST MEANDER OF THE LOW THROUGH THE
WEEKEND.

HOWEVER...NO SOLUTION IS TRULY OFF THE TABLE...SINCE THE STEERING
FLOW FOR THE LOW IS FORECAST TO BECOME QUITE WEAK ON THE SOUTHERN
PERIPHERY OF A PERSISTENT RIDGE ALOFT OVER THE EAST COAST. IN
FACT...THE RIDGE...IN CONJUNCTION WITH AN ELONGATED UPPER LOW
ANALYZED THIS MORNING FROM THE SE STATES TO THE YUCATAN
CHANNEL...WILL FAVOR THE DEVELOPMENT OF AT LEAST A BRIEF REX
BLOCK...WHICH WOULD INDEED FAVOR SLOW AND ERRATIC MOTION OF ANY
CYCLONE TRAPPED WITHIN IT. IT WILL LIKELY TAKE A KICKER SHORTWAVE
TROUGH TO MIGRATE SLOWLY FROM THE PAC NW TODAY TO THE MS VALLEY
EARLY NEXT WEEK TO FINALLY CAUSE THE LOW TO LIFT NE AND AWAY FROM
THE NC/VA COASTS EARLY NEXT WEEK.

WILL FOLLOW THE WPC-PREFERRED "COMPROMISE" SOLUTION BETWEEN THE TWO
MODEL CAMPS INDICATED ABOVE...BEST ILLUSTRATED BY A 12Z GFS/EC
BLEND...WHOSE RESPECTIVE MASS FIELDS ARE REALLY NOT TOO DISSIMILAR.

THE RESULTANT SENSIBLE WEATHER IMPACTS WILL BE INCREASING CLOUDS AND
PROBABILITY OF PRECIPITATION FROM THE SOUTH AND EAST BY LATE
THU...WITH THE LATTER PROBABILITIES RANGING FROM CHANCE OVER THE
COASTAL PLAIN AND EASTERN SANDHILLS TO SLIGHT CHANCE OVER THE
PIEDMONT. WITH THE LOW NEARBY AND FORECAST TO MOVE LITTLE...LIKELY
JUST TO THE SOUTH AND EAST OF CENTRAL NC...A PERSISTENCE FORECAST OF
SIMILAR POP DISTRIBUTION -HIGHEST CHANCES SE AND LOWEST NW- WILL BE
HARD TO BEAT THROUGH THE WEEKEND. PROVIDED THE TIMING OF THE KICKER
WAVE REMAINS CONSISTENT...MON MAY BE THE RELATIVE DRIEST DAY OF THE
PERIOD IN BRIEF SUBSIDENCE BEHIND THE LOW AND IN ADVANCE OF THE
FRONTAL SYSTEM ASSOCIATED WITH THE KICKER WAVE...FORECAST TO ARRIVE
ON SUN.

TEMPERATURES HAVE BEEN ADJUSTED DOWNWARD...INTO THE 70S MAINLY OVER
EASTERN AREAS...GIVEN THE EXPECTATION OF MORE CLOUDS AND HIGHER
PRECIPITATION CHANCES WITH THE MORE WESTWARD FORECAST SOLUTIONS FOR
THE LOW. IF THE LOW WERE TO STAY OFFSHORE AND FARTHER SE OF NC...THE
AIR MASS WOULD SUPPORT LOWER TO MIDDLE 80S...AND SOME UPPER 80S
PROBABLE BY TUE.

&&

 .AVIATION /18Z TUESDAY THROUGH SUNDAY/...
AS OF 115 PM TUESDAY...

24-HOUR TAF PERIOD: HIGH CONFIDENCE THAT VFR CONDITIONS WILL PREVAIL
THROUGH THE TAF PERIOD AS BERMUDA HIGH PRESSURE RIDGES INTO THE
CAROLINAS. WINDS WILL BE GENERALLY SOUTHWESTERLY AT 5-10 KTS THIS
AFT/EVE...DECREASING TO 5 KTS OR LESS AND BECOMING VARIABLE
OVERNIGHT. A FEW MID TO HIGH CLOUDS MAY DEVELOP DURING THE AFTERNOON
HOURS...CLEARING OVERNIGHT. WINDS WILL BECOME MORE SOUTHERLY TO
SOUTHEASTERLY ON WEDNESDAY.

LOOKING AHEAD: THE BIGGEST AVIATION IMPACT WILL COME LATER IN THE
WEEK OR INTO THE WEEKEND AS AN AREA OF LOW PRESSURE DEVELOPS OFF THE
SOUTHEAST U.S. COAST. MODELS STILL DIFFER ON THE TRACK/LOCATION AND
TIMING OF THIS SYSTEM AS IT PROGRESSES NORTHWARD...THUS CONDITIONS
BEYOND THURSDAY STILL REMAIN FAIRLY UNCERTAIN. EVEN IF THE SYSTEM
REMAINS OFFSHORE...ENHANCED EASTERLY ONSHORE FLOW COULD YIELD AN
INCREASED THREAT FOR MORNING STRATUS/FOG. SHOULD THE SYSTEM MOVE
ONSHORE...THERE WOULD BE AN INCREASED CHANCE FOR RAIN...STRONG
WINDS...AND REDUCED AVIATION CONDITIONS.

&&

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

&&

$$
SYNOPSIS...RAH
NEAR TERM...RAH
SHORT TERM...RAH
LONG TERM...RAH
AVIATION...RAH


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