Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000
FXUS62 KRAH 270813
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
412 AM EDT MON APR 27 2015

.SYNOPSIS...HIGH PRESSURE WILL BUILD IN FROM THE NORTHWEST THROUGH
TONIGHT AND LINGER OVER THE CAROLINAS THROUGH TUESDAY NIGHT.
MEANWHILE...AN AREA OF LOW PRESSURE WILL DEVELOP ALONG THE GULF
COAST...THEN TRACK UP THE SOUTHEAST AND MIDDLE ATLANTIC COAST WED
THROUGH THU.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 350 AM MONDAY...

TODAY WILL BE WARMER THAN RECENT DAYS...BUT STILL BELOW AVG OWING TO
THE INFLUENCE OF BELOW NORMAL HEIGHTS AROUND A DEEP...MEAN TROUGH
CENTERED NEAR NOVA SCOTIA. A COUPLE OF NOTABLE SHORTWAVE TROUGHS
ROTATING AROUND THE WSW QUADRANT OF THE UPPER LOW WILL PIVOT ACROSS
THE MID-ATLANTIC STATES TODAY. THE FIRST...INITIALLY OVER CENTRAL
IN...WILL TRACK ESE ACROSS THE APPALACHIANS AND NORTHERN NC...TO
NEAR THE NC OUTER BANKS BY 18Z. THE TRAILING ONE...INITIALLY OVER
LAKE MI...WILL TAKE A SLIGHTLY MORE NORTHERLY TRACK ACROSS THE
VIRGINIAS TONIGHT. WHILE MOISTURE WITH BOTH WILL BE LIMITED...
MARGINALLY COOLING TEMPERATURES ALOFT...IN CONJUNCTION WITH DIURNAL
HEATING THIS AFTERNOON...WILL LIKELY RESULT IN A BRIEF UPTICK OF
SHALLOW CU BASED AROUND 7-8 THOUSAND FT OVER THE NE PIEDMONT AND
NORTHERN COASTAL PLAIN TODAY. ALTHOUGH THE HRRR SUGGESTS THAT CU
WILL DEEPEN SUFFICIENTLY TO GENERATE A FEW MEASURABLE SHOWERS WITH
THE LEAD VORT MAX ACROSS THOSE SAME AREAS THROUGH EARLY
AFTERNOON...A DEEP AND DRY SUB-CLOUD LAYER -ONE INCREASINGLY SO WITH
TIME WITH DIURNAL HEATING- SHOULD CAUSE ANY ASSOCIATED SPRINKLE TO
EVAPORATE BEFORE REACHING THE SFC...IF ANY EVEN DEVELOP AMIDST LIGHT
NW DOWNSLOPE FLOW AS HIGH PRESSURE RIDGES IN FROM THE NW...AND
OTHERWISE DEEP DRYNESS. HIGHS IN THE MIDDLE 60S TO LOWER 70S.

SFC HIGH PRESSURE WILL CONTINUE TO RIDGE SOUTHEAST INTO THE MIDDLE
ATLANTIC STATES AND RESULT IN LIGHT NW STIRRING OR BRIEF PERIODS OF
CALM...WITH LOWS MOSTLY IN THE LOWER 40S. SOME UPPER 30S WILL BE
POSSIBLE IF/WHERE WINDS GO CALM FOR ANY LENGTH OF TIME...HOWEVER...
GIVEN PROJECTED LL THICKNESS VALUES NEAR 1325 M AND JUST PASSING
THIN CIRRUS.

&&

.SHORT TERM /TUESDAY AND TUESDAY NIGHT/...
AS OF 405 AM MONDAY...

AN UPPER LOW INITIALLY OVER NM WILL MIGRATE EAST ACROSS THE SOUTHERN
PLAINS AND LOWER MS VALLEY...WHILE S/W RIDGING ALOFT BRIEFLY EXPANDS
ACROSS THE SE STATES IN ADVANCE OF THE LOW. DRY SFC HIGH PRESSURE
WILL CONSEQUENTLY BUILD ACROSS AND LINGER OVER THE MIDDLE ATLANTIC
STATES THROUGH EARLY TUE NIGHT...THEN YIELD TO TOP-DOWN MOISTENING
AHEAD OF SFC LOW PRESSURE FORECAST TO DEVELOP AND GRADUALLY DEEPEN
FROM THE WESTERN GOM AND ALONG THE GULF COAST THROUGH TUE NIGHT.
ASSOCIATED CIRRUS ON TUE WILL PROGRESSIVELY THICKEN AND LOWER
OVERNIGHT AND CULMINATE IN A CHANCE OF RAIN OVER THE SOUTHERN AND
WESTERN PIEDMONT PRIOR TO DAYBREAK WED. HIGHS GENERALLY 65 TO 70
DEGREES. LOW TEMPS...INITIALLY DRIVEN BY RADIATIONAL COOLING BEFORE
CLOUDS THICKEN AND LOWER AND CAUSE TEMPERATURES TO STEADY OR RISE
SLIGHTLY AFTER MIDNIGHT...ONLY TO EVAPORATIONALLY COOL WHERE RAIN
OCCURS PRIOR TO DAYBREAK...IN THE MIDDLE 40S TO LOWER 50S.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
AS OF 300 AM MONDAY...

AN UNSETTLED START TO THE LONG TERM AS WEDNESDAY WILL FEATURE A DEEP
LONGWAVE TROUGH ACROSS THE OHIO VALLEY WITH THE POSSIBILITY OF A
CUTOFF UPPER LEVEL LOW HELPING TO DEVELOP AN ASSOCIATED SURFACE LOW
IN THE SOUTHERN STREAM WHICH WILL MOVE NORTHEAST ALONG THE COAST
AFFECTING CENTRAL NC FROM WEDNESDAY THROUGH THURSDAY AND POSSIBLY
INTO FRIDAY. A SOMEWHAT NON-TRADITIONAL IN-SITU CAD SCENARIO WILL
SET UP AS OVERRUNNING PRECIPITATION FALLS INTO A DRIER AIRMASS BELOW
WHICH WILL COOL THE LOW LEVELS SIGNIFICANTLY. THIS WILL DETER ANY
SEVERE THREAT DESPITE PLENTY OF FORCING ON MULTIPLE LEVELS. WHILE
DETAILS ON THE TIMING ARE STILL COMING INTO AGREEMENT...THE GENERAL
SCENARIO WILL HAVE RAIN MOVING INTO THE SW LATE TUESDAY NIGHT OR
EARLY WEDNESDAY MORNING AND CONTINUING THROUGH AT LEAST THURSDAY
AFTERNOON AS THE SURFACE LOW MOVES UP THE CAROLINA COAST. BOTH
MODELS ARE PRODUCING 2 DAY QPF TOTALS OF CLOSE TO AN INCH SO SOME
PERIODS OF MODERATE TO HEAVY RAIN WILL BE POSSIBLE. DETAILS START TO
BLUR THURSDAY NIGHT INTO FRIDAY AS BOTH MODELS SHOW AN UPPER LEVEL
LOW DIVING SOUTHWARD OUT OF CANADA BUT THE GFS PRODUCES A MUCH
STRONGER CUTOFF LOW THAN THE ECMWF BUT THE UPSHOT WILL GENERALLY BE
THE SAME WHICH IS SOME LINGERING LIGHTER PRECIPITATION INTO
FRIDAY...ESPECIALLY ACROSS THE NORTH.

THE LOW MOVES OFFSHORE FRIDAY NIGHT AND RIDGING BUILDS IN FROM THE
WEST...HELPING TO DRY THINGS OUT FOR THE WEEKEND. THE PROGRESSION OF
THE SURFACE HIGH IS YET TO BE DETERMINED BUT SUFFICE TO SAY THAT
THERE WILL BE A DRYING AND WARMING TREND THROUGH THE WEEKEND.
THEREFORE TEMPERATURES START OUT MIDWEEK IN THE UPPER 50S TO MID 60S
FOR HIGHS UNDER THE CAD AIRMASS BUT WILL CLIMB INTO THE UPPER 70S BY
THE END OF THE WEEKEND AND WILL FEEL MORE LIKE MAY AND LESS LIKE
MARCH.

&&

.AVIATION /06Z MONDAY THROUGH FRIDAY/...
AS OF 215 AM MONDAY...

CLEARING OF MID LEVEL CLOUDS FROM NORTHWEST TO SOUTHEAST AND
CONSEQUENT NEAR SATURATED CONDITIONS AT THE SURFACE MAY RESULT IN
THE DEVELOPMENT OF PATCHY SUB-VFR VISIBILITY RESTRICTIONS DURING THE
PRE-DAWN HOURS...BUT HEAVY DEW WILL BE MORE PREVALENT THAN FOG OWING
TO SHARPLY DRIER AIR JUST ABOVE THE MOIST SURFACE LAYER.
OTHERWISE... CALM TO LIGHT W TO WNW WINDS THIS MORNING WILL BECOME
NW AND INCREASE INTO THE 8-14 KT RANGE THIS AFTERNOON...WITH
OCCASIONAL GUSTINESS BETWEEN 15-20 KTS IN THE SEVERAL HOURS PRIOR TO
SUNSET. SKIES WILL BE RELATIVELY CLEAR THROUGHOUT THE DAY...ASIDE
FROM MAINLY FEW-SCT SHALLOW CUMULIFORM CLOUDS AROUND 7-8 THOUSAND
FT...WITH RELATIVE GREATEST COVERAGE FROM KRWI AND POINTS
NORTHEASTWARD...WHERE A BRIEF BKN CEILING AT THAT HEIGHT WILL BE
POSSIBLE MID-LATE AFTERNOON OWING TO THE APPROACH OF AN UPPER LEVEL
DISTURBANCE AND ASSOCIATED RELATIVE STRONGEST LIFT AND MOISTURE OVER
NE NC AND SE VA.

OUTLOOK: A COASTAL LOW PRESSURE SYSTEM WILL RESULT IN A GOOD CHANCE
OF SUB-VFR CONDITIONS AND RAIN WED-THU...WITH THE RELATIVE HIGHEST
PROBABILITY OF OCCURRENCE AND LOWEST AND LONGEST SUB-VFR
CONDITIONS...AT EASTERN TAF SITES.

&&

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

&&

$$

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


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