Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 160700 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 242 AM EDT WED APR 16 2014 .SYNOPSIS...UNSEASONABLY STRONG...POLAR HIGH PRESSURE WILL BUILD EAST ACROSS THE MIDDLE ATLANTIC AND NORTHEAST STATES THROUGH THURSDAY. && .NEAR TERM /THROUGH THURSDAY NIGHT/...
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AS OF 300 AM WEDNESDAY... TODAY: IN THE STRONGLY SUBSIDENT WAKE OF A SHORTWAVE TROUGH ALOFT NOW NEARING THE MIDDLE ATLANTIC COAST...THE ASSOCIATED SUBSIDENCE INVERSION AND DEEP DRYNESS ABOVE...WHICH WAS OBSERVED BY 00Z/16TH RAOB DATA UPSTREAM AT FFC AND BNA...WILL SPREAD EAST ACROSS THE CAROLINAS TODAY. A SUNNY DAY WILL RESULT...ALBEIT AN UNSEASONABLY CHILLY ONE...OWING TO BREEZY NORTHEASTERLY FLOW (PARTICULARLY FROM LATE MORNING THROUGH EARLY AFTERNOON IN THE COASTAL PLAIN) AROUND A POLAR HIGH FORECAST TO STRENGTHEN WHILE MIGRATING FROM THE OH VALLEY TO NEW ENGLAND. INDEED...DRY ADIABATIC MIXING THROUGH 900 MB...WITH A COUPLE OF DEGREES ADDED TO ACCOUNT FOR A USUAL SLIGHT COOL BIAS WITH THIS TECHNIQUE...SUPPORTS HIGHS IN ONLY THE LOWER TO MIDDLE 50S - SOME 20 DEGREES BELOW AVERAGE - AND THUS THREATENING THE RECORD LOW MAX OF 56 DEGREES FOR THE DAT AT KFAY. SEE CLIMATE SECTION BELOW. TONIGHT: PROJECTED LOW LEVEL THICKNESS VALUES AROUND 1305 METERS AT GSO AT 12Z THU...WITH OPTIMAL RADIATIONAL COOLING...WOULD SUPPORT MIDDLE 20S. HOWEVER...A PROJECTED 4-6 MB RISE TONIGHT IN MSL PRESSURE WITH THE AFOREMENTIONED STRENGTHENING HIGH TO OUR NORTH WILL LIKELY MAINTAIN A NORTHEASTERLY STIRRING FOR MOST AREAS...THOUGH WEAKEST AND WITH LIKELY PERIODS OF CALM IN CLOSEST PROXIMITY TO THE RIDGE AXIS...OVER THE WESTERN/SOUTHERN PIEDMONT. MEANWHILE THE NE STIRRING WILL BE MORE PRONOUNCED IN A STRONGER MSL PRESSURE GRADIENT/AWAY FROM THE RIDGE AXIS...OVER THE COASTAL PLAIN. IN ADDITION...ATLANTIC MOISTURE ADVECTION IN NORTHEASTERLY FLOW BENEATH THE CAPPING INVERSION MAY RESULT IN SCT TO BKN LOW CLOUDS MAINLY IN THE COASTAL PLAIN LATE. AS SUCH...TEMPERATURES ARE APT TO DISPLAY A RELATIVELY LARGE RANGE...FROM 28-30 DEGREES IN RURAL WESTERN PIEDMONT LOCATIONS (IN CLOSEST PROXIMITY TO THE RIDGE AXIS) TO AROUND FREEZING IN URBAN AREAS FROM RDU WESTWARD TO THE TRIAD...TO 33-36 DEGREES IN THE COASTAL PLAIN AND EASTERN SANDHILLS. A FROST ADVISORY WILL CONSEQUENTLY LIKELY BE NEEDED FOR THE COASTAL PLAIN...ISSUED FOR THE FIRST PERIOD/LATER TODAY. THU AND THU NIGHT: GRADUAL MODIFICATION OF THE UNSEASONABLY STRONG/1045 MB POLAR HIGH CENTERED OVER MAINE EARLY THU WILL ENSUE FOR THE LATTER HALF OF THE WEEK. THE AFOREMENTIONED MOISTURE IN NE FLOW WILL RESULT IN THE DEVELOPMENT/WESTWARD EXPANSION OF A MOSTLY SCATTERED STRATOCUMULUS FIELD WITH DIURNAL HEATING THU...PERHAPS BRIEFLY BROKEN IN EASTERN AREAS...WITH DRY ADIABATIC MIXING AGAIN THROUGH 900 MB SUPPORTIVE OF HIGHS MAINLY BETWEEN 60 AND 65 DEGREES -IN LINE WITH PROJECTED 24 HOUR LOW LEVEL THICKNESS RISES OF ABOUT 30 METERS OF THOSE OF WED. CHILLY WITH GOOD RADIATIONAL COOLING...DESPITE A FEW LINGERING STRATOCUMULUS AND THE ARRIVAL OF A THIN VEIL OF CIRRUS ATTENDING A SOUTHERN STREAM WAVE - LOWS OF 36 TO 42 DEGREES. PATCHY FROST WILL BE POSSIBLE IN RURAL WESTERN PIEDMONT LOCATIONS.
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&& .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... AS OF 240 AM WEDNESDAY... HIGH PRESSURE RIDGING INTO THE REGION FROM THE NE AND THE SUBSEQUENT NORTHEASTERLY WINDS WILL RESULT IN CONTINUED CAA INTO CENTRAL NC ON FRIDAY. FAIRLY CONFIDENT THERE WILL AT LEAST BE DESCENT COVERAGE OF HIGH CLOUDS OVER THE AREA SO...FOR NOW...EXPECT HIGHS ON FRIDAY MAINLY IN THE LOW TO MID 60S. THERE IS SOME UNCERTAINTY FOR THE FORECAST FRIDAY NIGHT INTO SATURDAY. BOTH MODELS HAVE AN UPPER LEVEL TROUGH MOVING THROUGH THE AREA...HOWEVER THE ECMWF CUTS OFF A LOW OFF THE COAST OF FL SATURDAY MORNING WHERE IT STALLS OUT...WHILE THE GFS TROUGH PROGRESSES OFF THE ATLANTIC COAST BY SATURDAY NIGHT. AS A RESULT...THE ECMWF FORECASTS RAIN MOVING INTO THE SOUTHEAST FRIDAY NIGHT/SATURDAY WHILE THE GFS REMAINS DRY. GIVEN THE UNCERTAINTY WILL KEEP FORECAST DRY...ALTHOUGH CONFIDENCE IS NOT PARTICULARLY HIGH. OVERNIGHT LOWS BOTH FRIDAY AND SATURDAY NIGHTS GENERALLY IN THE MID 40S NW TO AROUND 50 DEGREES SE. HIGHS WITH THE SURFACE RIDGE WEAKENING ON SATURDAY EXPECT HIGHS MAINLY IN THE LOW TO MID 70S. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... AS OF 240 AM WEDNESDAY... AS THE LOW OFF THE ATLANTIC COAST MOVES FURTHER AWAY FROM NC... EXPECT HIGH PRESSURE TO BUILD BACK INTO THE AREA FOR SUNDAY AND MONDAY...RESULTING IN MAINLY CLEAR/SUNNY SKIES AND DRY WEATHER. HIGHS MAINLY IN THE LOW TO MID 70S...LOWS SUNDAY NIGHT IN THE UPPER 40S TO AROUND 50 DEGREES. MODELS INDICATE AN UPPER LEVEL SHORTWAVE WILL APPROACH CENTRAL NC MONDAY NIGHT AND PROGRESS THROUGH THE AREA THROUGH TUESDAY NIGHT. THOUGH THE MODELS ARE NOT IN COMPLETE AGREEMENT WITH THE SPECIFICS ABOUT THIS FEATURE...THERE WILL AT LEAST BE A SLIGHT CHANCE FOR SOME RAIN DURING THIS TIME...THUS WILL KEEP SLIGHT CHANCES FOR RAIN IN THE FORECAST. HIGHS GENERALLY AROUND 70 DEGREES TUESDAY AND WEDNESDAY...WITH OVERNIGHT LOWS AROUND 50 DEGREES. && .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/... AS OF 200 AM WEDNESDAY... MVFR CLOUDS WILL LINGER THROUGH 09Z AT KRWI AND JUST EAST OF KRDU/KFAY...IN CLOSER PROXIMITY TO AN OFFSHORE/EASTBOUND COLD FRONT. OTHERWISE...CLEAR VFR CONDITIONS ARE EXPECTED THROUGH THE TAF PERIOD...AS UNSEASONABLY STRONG/POLAR HIGH PRESSURE BUILDS EAST ACROSS THE MID ATLANTIC REGION. THE INFLUX OF THE COLD/DRY AND DENSE AIR ASSOCIATED WITH THE HIGH WILL RESULT IN BREEZY CONDITIONS THROUGH MIDDAY-EARLY AFTERNOON...STRONGEST AT EASTERN TERMINALS... AND MAXIMIZED BETWEEN 14-17Z. ATLANTIC MOISTURE IN NE LOW LEVEL FLOW WILL RESULT IN THE WESTWARD EXPANSION/ADVECTION OF MVFR CLOUDS FROM COASTAL AREAS LATE TONIGHT...AND THIS COULD RESULT IN SCATTERED TO PERHAPS EVEN BROKEN STRATOCUMULUS AROUND 3000 FT...JUST BEYOND THE 06Z TAF PERIOD...MAINLY AT KRWI. OUTLOOK: THE AFOREMENTIONED MVFR MOISTURE WILL THEN EXPAND WESTWARD AND RESULT IN GENERALLY SCATTERED STRATOCUMULUS LIKELY JUST ABOVE 3000 FT AT ALL TERMINALS DURING THE DAY THU. IFR/LIFR CEILINGS POSSIBLE LATE THU NIGHT-EARLY FRI...AS THE BOUNDARY LAYER NOCTURNALLY COOLS AND MOISTURE IN ENE FLOW FURTHER INCREASES/RESULTS IN INCREASING RH AND CLOUD DEVELOPMENT). && .CLIMATE... THE FOLLOWING ARE THE RECORD LOW TEMPERATURES FOR WED AND THU MORNING... AND THE RECORD LOW MAXIMUM TEMPERATURES FOR WED: WED 04/16 THU 04/17 LOW/YEAR LOW MAX/YEAR LOW/YEAR FAY: 28/1943 56/1950 31/1953 GSO: 25/1943 48/1929 29/1953 RDU: 28/1950 46/1890 29/1962 && .RAH WATCHES/WARNINGS/ADVISORIES... FREEZE WATCH FROM LATE WEDNESDAY NIGHT THROUGH THURSDAY MORNING FOR NCZ007>011-021>027-038>041-073>077-083>086. FREEZE WARNING FROM 3 AM TO 9 AM EDT WEDNESDAY FOR NCZ007>010- 021>026-038>041-073>077-083-084. && $$ SYNOPSIS...MWS NEAR TERM...MWS SHORT TERM...KC LONG TERM...KC AVIATION...MWS CLIMATE...MWS

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