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[Printable]
709
FXUS62 KRAH 160818
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
418 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/...
AS OF 300 AM WEDNESDAY...

UPDATED FOR HEADLINE SECTION FOR UPGRADE OF FREEZE WATCH TO A
WARNING...FROM MIDNIGHT TO 9 AM THU...OVER ALL BUT THE COASTAL
PLAIN COUNTIES. A FREEZE WATCH REMAINS IN EFFECT FOR HALIFAX AND
NASH COUNTIES.

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.

&&

.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 TUESDAY/...
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 /08Z 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 WARNING UNTIL 9 AM EDT THIS MORNING FOR NCZ007>010-
021>026-038>041-073>077-083-084.
FREEZE WARNING FROM MIDNIGHT TONIGHT TO 10 AM EDT THURSDAY FOR
NCZ007>010-021>026-038>041-073>077-083>086.
FREEZE WATCH FROM LATE TONIGHT THROUGH THURSDAY MORNING FOR
NCZ011-027.

&&

$$
SYNOPSIS...MWS
NEAR TERM...MWS
SHORT TERM...KC
LONG TERM...KC
AVIATION...MWS
CLIMATE...MWS




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