Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 020116 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 915 PM EDT WED APR 1 2015 .SYNOPSIS...HIGH PRESSURE REMAINS OVER THE REGION INTO THURSDAY. HIGH PRESSURE DRIFTS EAST THURSDAY AND THURSDAY NIGHT...WITH A WARM SOUTHWEST FLOW FRIDAY AHEAD OF A COLD FRONT THAT SWEEPS ACROSS THE REGION FRIDAY NIGHT AND EARLY SATURDAY. HIGH PRESSURE RETURNS BY SATURDAY AFTERNOON...CONTINUING AT LEAST THROUGH SUNDAY. && .NEAR TERM /THROUGH TONIGHT/... AS OF 915 PM WEDNESDAY... NE TO SW ORIENTED SURFACE RIDGE AXIS AND SHORTWAVE RIDGING ALOFT WILL PROMOTE GOOD RADIATIONAL COOLING OF ANTECEDENT DRY AIRMASS IN PLACE. AS SFC DEWPOINTS MODERATE IN THE 30S...EXPECT OVERNIGHT LOWS TO RANGE FROM MID 30S NE TO LOWER 40 SW...COOLEST UNDERNEATH THE CENTER OF SFC RIDGE AXIS. PATCHY TO SCATTERED FROST WILL BE POSSIBLE ACROSS THE NORTHERN AND CENTRAL COASTAL PLAIN COUNTIES ...WITH A FROST ADVISORY IN EFFECT TONIGHT FOR EDGECOMBE...WILSON...JOHNSTON...AND WAYNE WHERE THE FROST/FREEZE PROGRAM BEGAN THIS PAST SUNDAY ON MARCH 29TH(THE REMAINDER NORTHERN THIRD OF THE FORECAST AREA WILL START APRIL 4TH). && .SHORT TERM /THURSDAY AND THURSDAY NIGHT/... AS OF 315 PM WEDNESDAY... THURSDAY... A S/W IN THE SOUTHERN STREAM CURRENTLY OVER THE SOUTHERN PLAINS WILL MOVE EASTWARD TONIGHT...AND APPROACH CENTRAL NC THURSDAY. THIS FEATURE WILL WEAKEN WITH TIME BUT STILL BACK THE MID- UPPER LEVEL FLOW TO A SWLY DIRECTION...RESULTING IN MOISTURE ADVECTION ALOFT. IN THE LOWER LEVELS...DEPARTING SFC RIDGE WILL CAUSE NEAR SURFACE WINDS TO BECOME SLY...ADVECTING A WARMER AIR MASS. SHOULD SEE AFTERNOON TEMPS REBOUND BACK INTO THE 70-75 DEGREE RANGE. IF CLOUDS ARE MORE EXTENSIVE/ARRIVE SOONER THAN EXPECTED IN THE WEST...MAX TEMPS MAY END UP BEING 2-3 DEGREES COOLER THAN FORECAST (TRIAD VICINITY). THURSDAY NIGHT... LOW LEVEL WARM ADVECTION WILL INCREASE SUBSTANTIALLY AS LOW LEVEL JET DEVELOPS OVERHEAD. THIS FEED OF WARM MOIST AIR WILL RESULT IN THE DEVELOPMENT OF LOW CLOUDS OVERNIGHT. LATEST WRF MODELS DEPICT A WEAKENING BAND OF SHOWERS CROSSING THE MOUNTAINS AROUND 00Z FRIDAY...WITH ISOLATED SHOWERS CROSSING THE PIEDMONT OVERNIGHT. PER RH CROSS SECTIONS...MOISTURE DOES NOT LOOK DEEP ENOUGH TO GENERATE ANYTHING MORE THAN DRIZZLE OR AN ISOLATED SHOWER. INHERITED A SLIGHT CHANCE POP AS FAR EAST AS THE WESTERN EDGE OF THE TRIANGLE. WILL TRIM BACK POPS A TAD AND KEEP ISOLATED SHOWER THREAT CONFINED TO THE FAR WESTERN PIEDMONT. EXTENSIVE CLOUDS AND A PERSISTENT SLY SFC WIND WILL RESULT IN MILD OVERNIGHT TEMPS. MIN TEMPS 55-60. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... AS OF 250 PM WEDNESDAY... IN THE MID-LEVELS FRIDAY...BOTH THE NAM AND THE GFS PROVIDE FOR A SHORTWAVE THAT MOVES THROUGH CENTRAL NORTH CAROLINA...STRONGER ON THE GFS AND WEAKENING AS IT MOVES THROUGH ON THE NAM. ON BOTH MODELS THE MEAN RELATIVE HUMIDITY ACTUALLY DECREASES DURING THE DAY...WITH UPPER CONVERGENCE ACTUALLY FORECAST ON THE GFS BY FRIDAY AFTERNOON AS SURFACE RIDGING BUILDS WEST BRIEFLY OVER THE EASTERN GULF. BUFR SOUNDINGS FROM BOTH THE NAM AND THE GFS SUGGEST LOW CLOUDS FRIDAY MORNING...FOLLOWED BY A FAIRLY CAPPED AIR MASS WITH JUST ENOUGH COOLING BETWEEN 850MB AND 700MB ON THE GFS BUFR SOUNDING TOWARD KRWI FRIDAY AFTERNOON THAT AN ISOLATED SHOWER OR THUNDERSTORM COULD OCCUR...AS MLCAPE IN THE LOWEST 2KM WILL BE TO 200J/KG. WILL NOT REMOVE ANY OF THE SLIGHT CHANCES FROM THE PREVIOUS FORECAST AS THE NAM BUFR SOUNDING EARLY FRIDAY MORNING NOTES SOME MID-LEVEL MOISTURE IN THE -10C TO -15C LAYER WITH THE APPROACHING SHORTWAVE TOWARD THE TRIAD...AND DESPITE A VERY DRY SUB-CLOUD LAYER RENEWED MID-LEVEL MOISTURE THERE OCCURS TOWARD 00Z SATURDAY. 925MB WINDS INCREASE TO 25 TO 35KT FRIDAY AFTERNOON...AND BOTH THE NAM AND GFS BUFR SOUNDINGS SUGGEST A FEW GUSTS FROM 35 TO 40MPH ARE POSSIBLE IN THE SOUTHWEST FLOW FRIDAY AFTERNOON. WITH DEW POINTS AT LEAST IN THE 50S...MINIMUM RELATIVE HUMIDITIES WILL BE TO NEAR 40 PERCENT. FRIDAY NIGHT INTO SATURDAY...THE GFS IS FASTER WITH THE TIMING OF THE COLD FRONT MOVING THROUGH CENTRAL NORTH CAROLINA...BUT BOTH THE GFS AND THE NAM SHOW AN INCREASE IN MOISTURE WITH THE GFS FORECASTING GOOD UPPER DIFFLUENCE FRIDAY NIGHT. THE RIGHT ENTRANCE REGION OF THE 300MB JET LAGS THE FRONT...BUT THE RIGHT ENTRANCE REGION OF THE 500MB JET DOES NOT LAG IT VERY MUCH...SUCH AS THERE SHOULD BE SUFFICIENT LIFT FOR AT LEAST SCATTERED SHOWERS. INSTABILITY DIMINISHES TOWARD CENTRAL NORTH CAROLINA WITH THE APPROACH OF THE FRONT...AS THE GFS REDUCES MLCAPE IN THE LOWEST 2KM TO NOT REGISTERING AND LIFTED INDICES ON BOTH THE NAM AND GFS ARE WARMER THAN 0C. ALSO...THE GFS 850MB THETA-E FORECAST SHOWS THE THETA-E RIDGE GETTING SQUEEZED ALONG AND AHEAD OF THE FRONT. GUIDANCE POPS ARE CURRENTLY CHANCE AND THE MEX MOS POPS HAVE TRENDED DOWNWARD...SO WILL KEEP HIGH CHANCES IN THE FORECAST AT THIS TIME FOR OVERNIGHT FRIDAY...PUSHING EAST QUICKLY SATURDAY MORNING AS THE AIR MASS DRIES AHEAD OF THE UPPER TROUGH. HEIGHT AND THICKNESS FALLS SHOULD RESULT IN LESS THAN 10F OF WARMING SATURDAY FROM LOWS FRIDAY NIGHT...FOR HIGHS FROM NEAR 60 IN THE TRIAD TO THE UPPER 60S TOWARD KFAY AND KCTZ. THICKNESS PACKING AND A TIGHT GRADIENT SHOULD RESULT IN BREEZY CONDITIONS...WITH BUFR SOUNDINGS SUGGESTIVE OF A FEW GUSTS AROUND OR JUST ABOVE 30MPH. MINIMUM RELATIVE HUMIDITIES COULD FALL BELOW 30 PERCENT...AND DEPENDING ON HOW MUCH RAIN OCCURS...SOME INCREASE IN FIRE DANGER COULD BE PRESENT THEN. SATURDAY NIGHT THROUGH WEDNESDAY...HIGH PRESSURE SHOULD BUILD OVERHEAD SATURDAY NIGHT...WITH THE SURFACE RIDGE AXIS MOVING QUICKLY EAST SUNDAY. THE COOLEST MORNING IN THIS PERIOD CERTAINLY LOOKS TO BE SUNDAY...WITH 1000-850MB THICKNESSES SUPPORTIVE OF 30S AND SOME MOS GUIDANCE TEMPERATURES JUST ABOVE FREEZING. WILL NOTE IN A COUPLE OF WEATHER GRIDS SOME PATCHY FROST EARLY SUNDAY MORNING IN COOL AIR UNDER THE HIGH...WITH A LIGHT WIND AND A LIKELY CLEAR SKY...ALTHOUGH SOME OF THE UPPER-LEVEL MOISTURE FIELDS HAVE AN INCREASE IN MOISTURE AT THAT LEVEL NOT TOO FAR AWAY AROUND 12Z SUNDAY. FOR THE REST OF THE LONG-TERM PERIOD...THE LONG-TERM GUIDANCE SEEMS CONSISTENT MOST DAYS WITH RESPECT TO A BACKING FLOW ALOFT...AND A BACKING FLOW AT THE SURFACE AS WELL WHICH SHOULD GRADUALLY BUILD MOISTURE FROM THE SOUTH AND SOUTHWEST. 1000-850MB THICKNESSES SUPPORT TEMPERATURES...BOTH HIGHS AND LOWS...INCREASING SUNDAY THROUGH WEDNESDAY...AND THE GENERAL PATTERN SUPPORTS THIS AS WELL. QPF IS PRESENT ON THE GFS AND ECMWF AS EARLY AS MONDAY...CONTINUING THROUGH THE REST OF THE LONG-TERM PERIOD. THE FLOW ALOFT BECOMES BROADLY DIFFLUENT...AND THERE ARE FORECAST MID-LEVEL SHORTWAVES MOVING THROUGH CENTRAL NORTH CAROLINA EACH DAY ON THE LONG-TERM GUIDANCE...WITH THE GFS STRONGER MONDAY AND WEDNESDAY IN THAT REGARD. THERE IS SOME DIFFERENCE CERTAINLY IN THE PROGRESS SOUTH OF THE NEXT COLD FRONT AT THE VERY END OF THIS LONG- TERM PERIOD...OTHERWISE...THERE APPEARS TO BE A LACK OF A DEFINING SURFACE FEATURE OVER CENTRAL NORTH CAROLINA FOR DEEP CONVECTION. IT MAY BE THAT DEEP CONVECTION OCCURS MORE SO BECAUSE OF GREATER INSTABILITY OVER HIGHER TERRAIN THEN DRIFTING SOUTHEAST...OR SIMILARLY FROM A SYNOPTIC BOUNDARY TO OUR NORTHWEST AND NORTH. OVERALL...SLIGHT CHANCE TO CHANCE POPS FOR CENTRAL NORTH CAROLINA MONDAY THROUGH WEDNESDAY...FOLLOWING AN EXPECTED PATTERN OF HIGHER CHANCES DIURNALLY THROUGH THE AFTERNOON AND EVENING WITH MOST OF THE HIGHER POPS ALONG AND WEST OF U.S. 1. FOR THIS FORECAST WILL HAVE MAXES IN THE 60S SUNDAY...LOWER TO MID 70S MONDAY...MID TO UPPER 70S TUESDAY...AND WITH MANY AREAS AROUND 80 WEDNESDAY. OVERNIGHT LOWS WILL GRADUALLY WARM AS WELL...WITH THE FORECAST FOR NOW VERY CLOSE TO RECORD HIGH MINIMUMS NEAR THE TRIAD TUESDAY NIGHT. && .AVIATION /00Z THURSDAY THROUGH MONDAY/... AS OF 815 PM WEDNESDAY... DRY AIR SURFACE RIDGE WILL EXTEND OVER THE AREA THROUGH 12Z THURSDAY...PROMOTING VFR CONDITIONS OVERNIGHT ALONG WITH LIGHT AND VARIABLE WINDS. AS SURFACE HIGH PUSHES OFFSHORE...SOUTHERLY WINDS WILL DEVELOP ACROSS THE AREA ON THURSDAY WITH MOISTURE BEGINNING TO INCREASE WEST TO EAST...ESPECIALLY DURING THE LATE AFTERNOON/AND EVENING...WITH LOW END VFR/HIGH MVFR CEILINGS DEVELOPING AT KINT AND KGSO BETWEEN 21 TO 00Z. A STRENGTHENING 35-40KT SWLY LOW-LEVEL JET WILL OVERSPREAD THE AREA THURSDAY NIGHT...LEADING TO THE DEVELOPMENT OF IFR TO MVFR STRATUS ACROSS THE AREA BETWEEN 06 TO 12Z ALONG WITH AN ISOLATED/SLIGHT CHANCE OF A SHOWER OR TWO...LOWEST IN THE WEST WHERE SREF PROB INDICATE A 80-90 PERCENT CHANCE OF IFR CONDITIONS. IN ADDITION...IF SFC WINDS DECOUPLE...THERE COULD BE A PERIOD OF LOW LEVEL WIND SHEAR (DUE TO SPEED SHEAR) AS WINDS AT 1500FT SHOULD BE SW AROUND 40KTS. AREAS OF MVFR/IFR FRIDAY MORNING SHOULD GIVE WAY TO VFR CONDITIONS BY EARLY AFTERNOON. IT WILL BE BREEZY FRIDAY AFTERNOON AS A FRONTAL SYSTEM APPROACHES FROM THE WEST. WIND GUSTS ON THE ORDER OF 25-30KTS POSSIBLE. A PERIOD OF SUB VFR CONDITIONS APPEAR LIKELY FRIDAY NIGHT INTO EARLY SATURDAY AS THE FRONT CROSSES THE REGION...ACCOMPANIED BY SCATTERED- NUMEROUS SHOWERS. A RETURN TO VFR CONDITIONS EXPECTED SATURDAY AFTERNOON...PERSISTING INTO SUNDAY AND MONDAY. && .RAH WATCHES/WARNINGS/ADVISORIES... FROST ADVISORY FROM 4 AM TO 8 AM EDT THURSDAY FOR NCZ028-042-043-078. && $$ SYNOPSIS...DJF NEAR TERM...CBL SHORT TERM...WSS LONG TERM...DJF AVIATION...CBL/WSS

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