Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 241916 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 316 PM EDT TUE MAR 24 2015 .SYNOPSIS...COOL HIGH PRESSURE WILL MOVE DOWN THE MID ATLANTIC COAST OVERNIGHT TONIGHT AND WEDNESDAY BEFORE A WARM FRONT PUSHES NORTHWARD WEDNESDAY NIGHT. WARMER AND MORE UNSETTLED CONDITIONS THURSDAY AHEAD OF A COLD FRONT THAT WILL MOVE THROUGH THE AREA ON FRIDAY. && .NEAR TERM /THROUGH TONIGHT/... AS OF 315 PM TUESDAY... MOSTLY CLEAR SKIES OVER THE CWA THIS AFTERNOON AS EARLIER STRATUS HAS BURNED OFF AND NC REMAINS BETWEEN LOW LEVEL CLOUDINESS TO THE SOUTH AS OBSERVED ON THE VISIBLE SATELLITE AND UPPER LEVEL CLOUDINESS TO THE NORTH...STEMMING FROM A SHORTWAVE OVER THE OHIO VALLEY...DEPICTED NICELY BY WATER VAPOR. AS A RESULT OF THE INCREASED INSOLATION...TEMPERATURES ARE A LITTLE BIT HIGHER THAN ANTICIPATED FOR THIS EARLY IN THE AFTERNOON AND WILL TOP OUT IN GENERALLY THE LOWER 60S WITH LOWER 70S POSSIBLE IN THE EXTREME SOUTHWEST. SKIES SHOULD REMAIN MOSTLY CLEAR FOR MUCH OF THE REMAINDER OF THE DAY BUT OROGRAPHICALLY INFLUENCED CLOUDINESS MAY START TO SPILL INTO NORTHWESTERN AREAS LATER THIS EVENING. EVENTUALLY...AS LOW PRESSURE BOWLS INTO THE GREAT LAKES REGION FROM THE CENTRAL PLAINS...THE SURFACE HIGH WILL MOVE FROM THE NORTHEAST...DOWN THE MID ATLANTIC COAST AND SET UP AN IN-SITU DAMMING SITUATION. THIS WILL CAUSE LOW CLOUDS TO OVERSPREAD THE AREA...PARTICULARLY IN THE TRIAD AND THIS WILL PERSIST THROUGH THE NIGHT. THERE IS A CHANCE FOR SOME DRIZZLE OR LIGHT RAIN WITH THE INCREASED DAMMING ACTIVITY BUT THIS SHOULD BE LIMITED. LOWS IN THE LOWER 40S NORTHEAST WHERE IT WILL TAKE LONGER FOR CLOUDS TO BUILD IN AND MORE RADIATION IS ALLOWED TO OCCUR. MID 40S TO NEAR 50 DEGREES ELSEWHERE. && .SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/... AS OF 315 PM TUESDAY... IN SITU CAD WEDGE WILL BE IN PLACE FOR MUCH OF THE DAY ON WEDNESDAY AND THIS WILL SET UP A DIFFERENTIAL HEATING GRADIENT WITH HIGHS ONLY TOPPING OUT IN THE UPPER 50S TO LOWER 60S IN THE TRIAD BUT POSSIBLY REACHING THE LOWER 70S IN THE SOUTHEAST. THIS DIFFERENCE IN TEMPERATURE COULD COME IN TO PLAY LATER IN THE DAY IN REGARDS TO DEVELOPING INSTABILITY AS HIGH PRESSURE OFF THE COAST WILL GRADUALLY SLIDE OUT TO SEA...THE WEDGE FRONT WILL BREAK DOWN AND IN ITS PLACE SOUTHERLY RETURN FLOW WITH A LOT OF LOW LEVEL MOISTURE TRANSPORT OFF OF THE SOUTHWEST ATLANTIC. AS FAR AS PRECIPITATION IS CONCERNED...ONLY LIGHT RAIN AND DRIZZLE ARE EXPECTED EARLY IN THE WEST UNDER THE CAD REGIME...BUT LATER IN THE EVENING AS THE HIGH SLIDES OUT TO SEA...MORE CONVECTIVE SHOWERS AND THUNDERSTORMS WILL BE POSSIBLE WEDNESDAY EVENING INTO WEDNESDAY NIGHT. CAPE IS TALL AND SKINNY AND MOISTURE IS VERY LIMITED TO THE LOW LEVELS BUT ANY CAPPING THAT IS IN PLACE INITIALLY AROUND THE 700 MB LEVEL WILL EVENTUALLY ERODE OVERNIGHT...SETTING UP MORE FAVORABLE CONDITIONS FOR CONVECTION ON WEDNESDAY NIGHT AND INTO THE DAY ON THURSDAY. WIND SHEAR WILL BE VERY FAVORABLE FOR CONVECTION AS 40 KTS OR SO OF BULK SHEAR IS EXPECTED. RAIN CHANCES WILL INCREASE SIGNIFICANTLY AFTER 6Z THURSDAY. A NON-DIURNAL TEMPERATURE TREND IS EXPECTED AS THE CAD BREAKS DOWN AND A SURFACE WARM FRONT WORKS NORTHWARD THROUGH THE AREA. THEREFORE NEAR STEADY TO SLIGHTLY INCREASING TEMPERATURES AFTER 00Z THURSDAY WILL MORE RAPIDLY INCREASE EARLY THURSDAY MORNING. LOWS LISTED IN THE LOW TO UPPER 50S BUT AGAIN THIS WILL OCCUR EARLIER WEDNESDAY NIGHT AS OPPOSED TO THURSDAY MORNING. && .LONG TERM /THURSDAY THROUGH MONDAY/... AS OF 330 AM TUESDAY... LOOKING AT TEMPS WAY UP IN THE 70S TO LOWER 80S ON THURSDAY WITH DEEP SOUTHWEST WARM AIR ADVECTION AHEAD OF AN APPROACHING COLD FRONT. INSTABILITY WILL BE QUITE HIGH...WITH MID LEVEL LAPSE RATES >6C AND FORECAST CAPES OF ~1K JOULES. SHOWER COVERAGE SHOULD BE DECENT...BUT NO GOOD TRIGGERING MECHANISM ALONG WITH UNIDIRECTIONAL FLOW AND WEAK UPPER DIFFLUENCE MAKE THUNDER A LITTLE LESS LIKELY...WILL HAVE HIGH CHANCE POPS AND SLIGHT CHANCES FOR THUNDER DURING THE FAVORED MAX HEATING INTO EARLY EVENING TIME FRAME. WILL MAINTAIN CHANCES OF ANAFRONTAL SHOWERS THROUGH THE NIGHT WHICH WILL ACCOMPANY THE SURGE OF COLDER AIR BEHIND THE SURFACE FRONT WHICH MOVES THROUGH AROUND MIDNIGHT. COLD AIR ADVECTION AND AT LEAST SOME CLEARING WILL BE UNDERWAY IN THE WEST BY SUNRISE WITH MINS IN THE MID 40S NORTHWEST TO LOWER 50S SOUTHEAST. INITIAL SURGE OF COLD AIR ADVECTION FRIDAY WILL BE AUGMENTED BY AN ADDITIONAL STRONG SHORT WAVE IN THE MID LEVEL FLOW WHICH WILL MOVE ACROSS THE AREA EARLY FRIDAY NIGHT. THE SHORT WAVE LOOKS QUITE VIGOROUS AND EXPECT SHOWERS OUT OF THE STRATOCUMULUS ACCOMPANYING THE WAVE...MAINLY THROUGH AROUND MIDNIGHT. THE AMPLIFIED LONG WAVE TROF OVER THE EASTERN CONUS WILL PIVOT ACROSS THE AREA AS THE SHORT WAVE LIFTS OUT LATER FRIDAY NIGHT. LOW LEVEL THICKNESS VALUES WILL CORRESPONDINGLY CRASH AND WITH MOSTLY CLEAR SKIES BY SATURDAY MORNING...MINS WILL BE MID TO UPPER 30S TO KICK OFF THE WEEKEND. COOL AIRMASS WILL BE IN PLACE FOR THE REMAINDER OF THE WEEKEND WITH SATURDAY AS OUR COOLEST DAY...WITH HIGHS IN THE NORTHWEST IN THE UPPER 40S...WITH MOSTLY LOWER 50S ELSEWHERE. SURFACE HIGH PRESSURE OVERHEAD WILL PRODUCE NEAR IDEAL RADIATIONAL CONDITIONS SATURDAY NIGHT WITH CLEAR SKIES AND CALM WINDS...AND MORNING LOWS SUNDAY MORNING WILL EDGE A DEGREE OR TWO BELOW FREEZING OVER ALL BUT THE SOUTHEAST. STRONG SUN AND BUILDING HEIGHTS ALOFT WILL ALLOW RECOVERY TO COMMENCE SUNDAY...WITH HIGHS IN THE UPPER 50S TO LOWER 60S...WARMING TO MOSTLY MID 60S ON MONDAY. && .AVIATION /18Z TUESDAY THROUGH SUNDAY/... AS OF 200 PM TUESDAY... 24 HOUR TAF PERIOD: VFR CONDITIONS INITIALLY WILL PERSIST FOR THE AFTERNOON AND INTO THE EVENING BUT LATE EVENING EXPECT CEILINGS TO START COMING DOWN STEADILY AND ALL SITES WILL REALIZE AT LEAST IFR CONDITIONS OVERNIGHT TONIGHT WITH THE TRIAD SITES POSSIBLY GETTING DOWN TO LIFR. RELATIVE HUMIDITY CROSS SECTIONS SHOW THAT ONCE CEILINGS ARE DOWN THEY WILL PROBABLY STAY DOWN THROUGH THE TAF PERIOD...EXCEPT IN THE SOUTH AND EAST WHERE THEY MAY IMPROVE A LITTLE BUT NOT TO VFR LEVELS. THE TRIAD SITES WILL CERTAINLY BE THE MOST PESSIMISTIC AS COLD AIR DAMMING SCENARIO SETS IN. WINDS WILL BE PREDOMINANTLY EASTERLY BUT FAIRLY LIGHT AT AROUND 5 KTS. A SLIGHT CHANCE OF SOME DRIZZLE ACROSS THE NORTH WILL BE POSSIBLE TONIGHT. LONG TERM: CONDITIONS MAY IMPROVE BRIEFLY WEDNESDAY EVENING BUT THEN MORE FOG/LOW STRATUS IS EXPECTED THURSDAY MORNING WITH INCREASED RAIN CHANCES. THURSDAY AFTERNOON/EVENING WILL FEATURE CHANCES FOR CONVECTION IN THE WARM SECTOR AHEAD OF A COLD FRONT WHICH WILL MOVE THROUGH ON FRIDAY. CONDITIONS SHOULD RETURN TO VFR LEVELS FOR THE WEEKEND. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...ELLIS NEAR TERM...ELLIS SHORT TERM...ELLIS LONG TERM...MLM AVIATION...ELLIS

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