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/...
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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.
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&& .SHORT TERM /TUESDAY AND TUESDAY NIGHT/...
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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.
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&& .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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