Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 270620 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 220 AM EDT MON APR 27 2015 .SYNOPSIS...
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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.
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&& .NEAR TERM /THROUGH TONIGHT/... AS OF 925 PM SUNDAY... IN THE LAST COUPLE OF HOURS WE`VE SEEN A RESURGENCE OF SHOWERS OVER THE SOUTHERN PORTIONS OF THE FORECAST AREA... LIKELY DUE IN PART TO AN UPTICK IN PRECIPITABLE WATER (AS NOTED ON BLENDED TPW IMAGERY) ALONG A LOW LEVEL CONVERGENCE ZONE NOTED AROUND 850 MB. ONCE THIS CONTINUES TO PUSH STEADILY SOUTHWARD OVER THE NEXT FEW HOURS... WE SHOULD SEE A GRADUAL DECLINE IN SHOWER COVERAGE. HAVE RETAINED A FEW SHOWERS IN SOUTHERN SECTIONS UNTIL SHORTLY AFTER MIDNIGHT... FOLLOWING THE TIMING SUGGESTED BY BOTH EXTRAPOLATION AND BY THE LATEST HIGH-RES MODELS. EXPECT DRYING OVERNIGHT FROM NW TO SE AS LOWER SURFACE DEWPOINTS SLOWLY FILTER IN FROM THE NORTHWEST... WITH DRYING FURTHER ALOFT AT 925-700 MB... AND THE ONSET OF LOW LEVEL DOWNSLOPE FLOW LATE. MOISTURE ALOFT NEAR 700 MB WILL BE LAST TO EXIT TO THE EAST... SO EXPECT MAINLY BROKEN MID CLOUDS TO PERSIST FOR MUCH OF THE NIGHT... WHICH WILL LIMIT RADIATIONAL COOLING UNTIL LATE TONIGHT AND APPROACHING DAYBREAK. THIS IN TURN SHOULD LIMIT FOG AND STRATUS FORMATION... ALTHOUGH POCKETS OF LOWER CLOUDS WILL REMAIN POSSIBLE WITH LIGHT WINDS AND A LOW TEMP/DEWPOINT SPREAD. NORTHERN SECTIONS ARE ALREADY SEEING TEMPS DROPPING INTO THE UPPER 40S HOWEVER... SO STILL EXPECT LOWS TO BE IN THE 40S EVERYWHERE... RANGING FROM AROUND 41 NORTH TO 48 FAR SOUTH... UNDER PARTLY TO MOSTLY CLOUDY SKIES... CLEARING LATE. -GIH && .SHORT TERM /MONDAY AND MONDAY NIGHT/... AS OF 245 PM SUNDAY... MONDAY...A MINOR S/W WILL CROSS THE NORTHERN MID ATLANTIC MONDAY...BRUSHING NE NC IN THE LATE AFTERNOON. THIS FEATURE WILL LIKELY ENHANCE STRATOCU COVERAGE OVER THE NORTHERN COASTAL PLAIN WITH AN ISOLATED PATCH OF LIGHT RAIN POSSIBLE. ELSEWHERE THE SUN WILL MAKE AN APPEARANCE. A STEADY NW LOW LEVEL FLOW WILL AID TO DIMINISH ANY LINGERING LOW CLOUD COVER OVER THE REST OF THE PIEDMONT AND SANDHILLS. TEMPERATURES WILL RECOVER NICELY IN THIS DOWNSLOPE WIND REGIME. AFTERNOON TEMPS WILL VARY FROM THE MID-UPPER 60S IN THE PIEDMONT/NORTHERN COASTAL PLAIN TO AROUND 70 IN THE SE. MONDAY NIGHT...NOSE OF SFC RIDGE WILL EXTEND ACROSS THE REGION. DRY AIR UNDERNEATH THIS RIDGE WILL RESULT IN MOSTLY CLEAR SKIES. MIN TEMPS WILL BE CHILLY..DIPPING INTO THE UPPER 30S AND LOWER 40S. AT THIS TIME...NOT EXPECTING TEMPS TO DIP BELOW 37 DEGREES. THUS PATCHY LIGHT FROST NOT A CONCERN...BUT WILL CONTINUE TO MONITOR. && .LONG TERM /TUESDAY THROUGH SUNDAY/... AS OF 320 PM SUNDAY... TUESDAY AND TUESDAY NIGHT: BRIEF S/W RIDGING WILL BUILD OVER THE AREA ON TUESDAY... WITH A SURFACE RIDGE AXIS INITIALLY EXTENDING INTO THE AREA FROM THE NORTHWEST (BEFORE A PIECE OF THE HIGH BREAKS OFF OVER THE CAROLINAS). THIS SHOULD ALLOW FOR MOSTLY SUNNY TO PARTLY SUNNY SKIES... WITH LOW LEVEL THICKNESS VALUES STILL RUNNING AT LEAST SOME 20-25 METERS BELOW NORMAL. GIVEN THIS EXPECT WE SHOULD SEE HIGH TEMPS GENERALLY IN THE 60S... WITH PERHAPS A FEW LOCATIONS TOUCHING 70 ACROSS THE SOUTH/SOUTHEAST. CLOUD COVER WILL QUICKLY THICKEN ON TUESDAY NIGHT/EARLY WEDNESDAY MORNING IN ADVANCE OF A SOUTHERN STREAM SYSTEM... WITH POSSIBLY SOME RAIN SPREADING INTO THE SOUTHWESTERN/WESTERN PORTIONS OF THE AREA NEAR DAYBREAK WEDNESDAY PER THE GFS AND ECMWF. THE LATEST NAM (12Z/26TH) HAS PRECIP SPREADING INTO SOUTHERN PORTIONS OF THE AREA BY MID TO LATE TUESDAY EVENING EVEN. GIVEN THIS SEEMS TO BE A FAST OUTLIER WILL CONTINUE TO TREND TOWARDS A BLEND OF THE GFS/ECMWF FOR THIS PERIOD OF THE FORECAST. WRT LOW TEMPS... WILL SHOW A RANGE FROM THE MID 40S NE (WHERE WE WILL HAVE THE BEST NOCTURNAL COOLING) TO AROUND 50 SW. HOWEVER... WITH A DRIER SURFACE AIRMASS IN PLACE WE SHOULD SEE TEMPS BEGIN TO WETBULB WITH THE ARRIVAL OF THE PRECIP. THUS... TEMPS MAY FALL AFTER SUNSET SOME IN THE SW FROM THE LOSS OF DAYTIME HEATING... THEN STABILIZE BY MID TO LATE EVENING WITH THE INCREASING/THICKENING CLOUD COVER... BEFORE ONCE AGAIN FALLING WITH AS THE RAIN ARRIVES. THUS... LOW TEMPS ARE TRICKY FOR WEDNESDAY MORNING AND WILL BE DEPENDENT ON THE TIMING AND INTENSITY OF THE RAIN FOR LOCATIONS THAT DO INDEED SEE PRECIP MOVE INTO THE AREA DURING THE EARLY MORNING HOURS OF WEDNESDAY. WEDNESDAY THROUGH FRIDAY NIGHT: MEDIUM RANGE MODELS ARE IN BETTER AGREEMENT TODAY IN SHOWING A SOUTHERN STREAM MID LEVEL LOW OVER NORTHERN TX TO BEGIN THE WEEK TRANSLATING EASTWARD AND SPAWNING A SURFACE LOW NEAR THE GULF COAST... THEN TRACKING TOWARDS OUR REGION TUESDAY NIGHT INTO WEDNESDAY... WITH THE EXPECTED SURFACE LOW TRACKING EASTWARD-NORTHEASTWARD AND EVENTUALLY NORTHEASTWARD ALONG OUR COAST BY THURSDAY MORNING. GIVEN THE RATHER DRY AIRMASS PRECEDING THIS SYSTEM... EXPECT WE SHOULD SEE A CAD AIRMASS DEVELOP ACROSS CENTRAL NC ON WEDNESDAY AS RAIN OVERSPREADS THE REGION FROM SOUTHWEST TO NORTHEAST (POSSIBLY BEGINNING DURING THE EARLY MORNING HOURS OF WEDNESDAY (AGAIN... WE STAYED CLOSE TO GFS/ECMWF FOR TIMING). THE CAD AIRMASS IS EXPECTED TO LINGER ACROSS PORTIONS OF CENTRAL NC ON THURSDAY (WITH BELOW NORMAL TEMPS EVEN EXPECTED FOR LOCATIONS THAT EVEN SEE SOME BREAKS IN THE CLOUDS STILL)... BEFORE SLOWLY ERODING ON THURSDAY NIGHT INTO FRIDAY AS THE SURFACE LOW LIFTS OFF TO THE NORTHEAST... YIELDING MORE OF A NORTH TO NORTHWESTERLY LOW TO MID LEVEL FLOW. CHANCES FOR RAIN SHOULD BEGIN TO DECREASE BY LATE THURSDAY INTO THURSDAY EVENING... WITH GENERALLY DRY WEATHER AGAIN EXPECTED BY FRIDAY. HIGH TEMPS ON WEDNESDAY ARE EXPECTED TO BE WELL BELOW NORMAL WITH THE EXPECTED CAD DEVELOPMENT. FOR NOW HAVE LOWERED HIGHS INTO THE MID TO UPPER 50S NW TO THE MID 60S FAR NE FOR WEDNESDAY. HIGHS THURSDAY AND FRIDAY IN THE 60S TO NEAR 70 ON FRIDAY IN THE SOUTH... STILL BELOW NORMAL. LOWS ARE EXPECTED TO BE IN THE UPPER 40S TO LOWER 50S FOR THE PERIOD. SATURDAY THROUGH SUNDAY: MID LEVEL HEIGHTS ARE EXPECTED TO RISE NEXT WEEKEND. THIS COUPLED WITH HIGH PRESSURE AT THE SURFACE WILL ALLOW FOR A WARMING A DRYING TREND IN CENTRAL NC. THIS SHOULD RESULT IN HIGHS IN THE 70S AND LOWS IN THE 50S... NEAR NORMAL FOR THIS TIME OF YEAR... WITH POSSIBLY EVEN ABOVE NORMAL HIGHS FOR SUNDAY AFTERNOON (MAYBE SOME LOW 80S). && .AVIATION /06Z MONDAY THROUGH FRIDAY/...
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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.
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&& .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...RAH NEAR TERM...HARTFIELD SHORT TERM...WSS LONG TERM...BSD AVIATION...RAH

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