Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 022043 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 343 PM EST MON MAR 2 2015 .SYNOPSIS...
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HIGH PRESSURE WILL BUILD INTO THE REGION FROM THE NORTH TONIGHT AND WILL SHIFT OFFSHORE DURING THE DAY TUESDAY AS A LOW PRESSURE SYSTEM TRACKS NORTHEAST FROM THE CENTRAL PLAINS INTO THE GREAT LAKES.
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&& .NEAR TERM /TONIGHT THROUGH TUESDAY NIGHT/...
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AS OF 330 PM MONDAY... IN THE WAKE OF THE COLD FRONT PASSAGE EARLIER TODAY...A STRONG BUT TRANSIENT +1030MB SURFACE HIGH WILL BUILD EAST ACROSS THE AREA TONIGHT...AND THEN MOVE OFFSHORE DURING THE DAY ON TUESDAY. IN A BROAD REGION OF WAA WELL DOWNSTREAM OF AN AREA OF LOW PRESSURE MOVING EASTWARD FROM THE ROCKIES INTO THE UPPER MS VALLEY AND GREAT LAKES REGION...STRENGTHENING SOUTHERLY ISENTROPIC LIFT ATOP THE SURFACE WEDGE OF COLD HIGH PRESSURE WILL RESULT IN THE DEVELOPMENT OF IN-SITU DAMMING ACROSS THE AREA ON TUESDAY. LITTLE IF ANY UPPER LEVEL FORCING ANTICIPATED ACROSS THE AREA. IN FACT...500MB HEIGHTS ACTUALLY RISE THROUGHOUT THE DAY ON TUESDAY. AS SUCH...PRECIPITATION WILL BE VERY LIGHT ACROSS THE AREA...SO LIGHT THAT THE BIG 4 IN WEATHER MODELS(GFS,NAM,EC,CANADIAN)....GENERATE ONLY A FEW HUNDREDTHS ACROSS THE CWA THROUGH 00Z WEDNESDAY. PATCHY RAIN AND/OR DRIZZLE LOOKS TO DEVELOP ACROSS THE WESTERN PIEDMONT BETWEEN 06-12Z...IN A ZONE OF SELY UPSLOPE COMPONENT EAST OF THE MOUNTAINS...WITH PATCHY RAIN/DRIZZLE THEN POSSIBLE ACROSS THE REMAINDER OF THE FORECAST AREA INTO THE AFTERNOON AND INTO THE EVENING WITHIN THE BROAD WAA REGIME. CONCERNING P-TYPE....GIVEN TRANSIENT NATURE OF HIGH...COLD AIR IS VERY SHALLOW AND LESS LIKELY TO SUPPORT ANY SUBSTANTIAL FROZEN OF FREEZING PRECIP. PRECIP IS EXPECTED TO FALL AS MOSTLY A COLD/CHILLY RAIN. HOWEVER THE EXCEPTION MAY BE ACROSS THE NORTHERN PIEDMONT/NORTHERN COASTAL PLAIN...NEAR THE NC/VA BORDER WHERE WE WILL SEE DECENT RADIATIONAL COOLING ACROSS THE AREA THIS EVENING...WHICH COULD ALLOW LOWS TONIGHT TO FALL INTO THE UPPER 20S/NEAR 30. IF PRECIP CAN MAKE IT INTO THE NORTHERN PIEDMONT/NE COASTAL PLAIN TUESDAY MORNING BEFORE THE MARCH SUN WARMS TEMPERATURES BACK ABOVE FREEZING... WE COULD SEE A BRIEF PERIOD OF LIGHT FREEZING RAIN/DRIZZLE BEFORE CHANGING OVER TO RAIN. DO NOT EXPECT IMPACTS...THUS NO ADVISORY WILL BE ISSUED. HOWEVER EVENING AND MIDNIGHT SHIFTS WILL MONITOR TRENDS AND ADJUST AS NEEDED. LOWS TONIGHT RANGING FROM NEAR 30 NE TO UPPER 30S SOUTHWEST. EXPECT NEAR STEADY TEMPERATURES ON TUESDAY...IN THE LOWER/MID 30S NORTH TO UPPER 30S/NEAR 40 SOUTH. A WARM FRONT IS EXPECTED TO LIFT NORTHWARD TOWARD CENTRAL NC TUE NIGHT...WITH TEMPERATURES RISING OVERNIGHT ACROSS MUCH OF THE AREA...ALTHOUGH THEY COULD REMAIN NEAR STEADY IN THE N/NW PIEDMONT. LIGHT RAIN/DRIZZLE COULD TAPER AS THE WARM FRONT LIFTS WITH EXPANDING FOG CONDITIONS POSSIBLE.
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&& .SHORT TERM /WEDNESDAY THROUGH THURSDAY/... AS OF 300 PM MONDAY... THE FORECAST PROBLEM FOR THIS PART OF THE FORECAST CONTINUES TO BE THE UNCERTAINTY IN TEMPERATURES DUE TO THE POTENTIALLY LINGERING WEDGE AND THE TIMING AND EXTENT TO WHICH THE WARM FRONT RETREATS NORTHWARD. GIVEN THAT THE MODELS HAVE A TENDENCY TO ERODE THE WEDGE TOO QUICKLY...ESPECIALLY IF THERE IS PRECIPITATION FALLING INTO IT...CURRENTLY FORECAST THE WEDGE STICKING AROUND INTO WEDNESDAY AFTERNOON IN THE FAR NW PIEDMONT...WITH A LARGE SPREAD IN TEMPS FROM NW TO SE ACROSS THE AREA. CONFIDENCE REMAINS SOMEWHAT LOW WITH RESPECT TO TEMPS...AS ANY CHANGES TO THE TIMING AND POSITION OF THE WEDGE/WARM FRONT AS THEY ERODE/RETREAT NORTHWARD WILL HIGHLY IMPACT TEMPERATURES. THEY WILL HOWEVER INCREASE GRADUALLY THROUGH AROUND MIDNIGHT THURSDAY BEFORE THE COLD FRONT BEGINS MOVING INTO THE NW. KEEPING IN MIND THE POTENTIAL MARGIN FOR ERRORS...FORECAST HIGH TEMPS IN THE MID 60S NW TO MID 70S SE ON WEDNESDAY. A NORMAL DIURNAL TEMPERATURE CURVE SHOULD RETURN WEDNESDAY NIGHT...ALTHOUGH THE TEMPERATURE GRADIENT WILL BE QUITE LARGE AND WILL DEPEND ON THE TIMING AND POSITION OF THE COLD FRONT...EXPECT LOWS IN THE UPPER 30S NORTH TO LOW 50S SOUTH WEDNESDAY NIGHT AND HIGHS IN THE LOW 40S NORTH TO MID 50S SOUTH ON THURSDAY AND DECREASING BEHIND THE FRONT. PRECIPITATION: THERE WILL BE A SLIGHT CHANCE OF PRECIP...MAINLY ACROSS THE WESTERN PORTIONS OF THE AREA WEDNESDAY...EVEN THOUGH THE MAIN PRE-FRONTAL CONVECTIVE RAINFALL REMAINS LARGELY ALONG OR WEST OF THE APPALACHIANS UNTIL WEDNESDAY AFT/EVE. SOUTHWESTERLY WINDS WILL BE QUITE STRONG ON WEDNESDAY AFT/EVE AS THE GRADIENT TIGHTENS AHEAD OF THE FRONT. LATE WEDNESDAY AFTERNOON IS STARTING TO SHAPE UP AS A HIGH SHEAR/LOW CAPE EVENT. FORECAST SOUNDINGS INDICATE 200-300 JOULES OF CAPE AND 0-3 KM SHEAR VALUES AROUND 35 KTS...MAINLY ALONG AND EAST OF I-95 AT THIS TIME. WITH SURFACE TEMPS EXPECTED IN THE MID 70S AND DEWPOINTS AROUND 60 DEGREES...THUNDERSTORMS WILL BE POSSIBLE WEDNESDAY AFTERNOON...THUS WILL INTRODUCE A SLIGHT CHANCE ACROSS THE EAST WITH THIS AFTERNOON`S FORECAST. THE LATEST 12Z ECMWF AND GFS MODEL RUNS ARE IN BETTER AGREEMENT WITH THE TIMING OF THE FROPA AND THE ASSOCIATED RAINFALL AS IT MOVES THROUGH THE AREA. THE LATEST RUNS SUGGEST THAT RAIN WILL BE LIKELY WEDNESDAY NIGHT... PROGRESSING NW TO SE THROUGH CENTRAL NC THROUGH MIDNIGHT FRIDAY. THIS REMAINS CASE OF THE COLD AIR CHASING THE PRECIP...BUT FOR NOW STILL EXPECT ALL PRECIP TO FALL AS RAIN...HOWEVER THERE IS A SMALL CHANCE THAT A FEW SNOWFLAKES COULD MIX IN ON THE TAIL END OF THE EVENT. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... AS OF 300 PM MONDAY... FRIDAY THROUGH SATURDAY: HIGH PRESSURE WILL BUILD IN BEHIND THE FRONT THURSDAY NIGHT...REMAINING OVER THE REGION INTO THE WEEKEND. EXPECT A DRY FORECAST FRIDAY THROUGH SATURDAY...WITH HIGHS IN THE UPPER 30S TO LOW 40S FRIDAY...INCREASING THROUGH THE WEEKEND AND INTO THE UPPER 50S TO LOW 60S BY MONDAY. LOWS WILL SEE A SIMILAR TREND...INCREASING FROM MAINLY LOW 20S LOW 20S THU AND FRI NIGHTS TO THE LOW TO MID 30S BY SAT AND SUN NIGHTS. THERE IS SOME MODEL DISAGREEMENT TOWARD THE END OF THE PERIOD WITH REGARD TO PRECIP CHANCES...AS THE ECMWF BRINGS PRECIP IN FROM THE SOUTHWEST SUNDAY NIGHT AND THE GFS IS COMPLETELY DRY. WILL FORECAST A SLIGHT CHANCE FOR RAIN SUN NIGHT/MONDAY...ALTHOUGH CONFIDENCE IS LOW AT THIS TIME. && .AVIATION /18Z MONDAY THROUGH SATURDAY/... AS OF 115 PM MONDAY... 24-HR TAF PERIOD: A STRONG BUT TRANSIENT +1030MB SURFACE HIGH WILL BUILD EAST ACROSS THE AREA THIS AFTERNOON AND TONIGHT IN THE WAKE OF THE COLD FRONT PASSAGE EARLIER TODAY. DRY AIR ADVECTION ALONG AND BEHIND THE FRONT HAS RESULTED IN VFR CONDITIONS ACROSS THE AREA. WILL SEE NWLY WIND GUSTS INTO THE UPPER TEENS IMMEDIATELY BEHIND THE FRONT...BECOMING LIGHT THIS EVENING FROM THE EAST-NORTHEAST. AVIATION CONDITIONS WILL QUICKLY DETERIORATE TONIGHT...ESPECIALLY ACROSS THE WESTERN PIEDMONT(KINT AND KGSO)WITH MVFR/IFR CEILINGS RETURNING BETWEEN MIDNIGHT AND SUNRISE TUE MORNING AS THE SFC HIGH MOVES QUICKLY OFFSHORE...ALLOWING LOW-LEVEL SOUTHERLY RETURN FLOW TO DEVELOP WITH PATCHY LIGHT RAIN/DZ. ITS POSSIBLE THAT AREAS ALONG AND NEAR THE NC/VA BORDER MAY SEE A BRIEF PERIOD OF FREEZING RAIN/DRIZZLE TUESDAY MORNING...BEFORE CHANGING OVER TO A COLD RAIN THEREAFTER AS TEMPERATURES WARM INTO THE LOWER/MID 30S. CONFIDENCE IS MUCH LOWER AT KRDU...KRWI...KFAY...WHERE THERE IS A LARGE SPREAD IN THE MODEL GUIDANCE. SOME MODEL GUIDANCE SUGGESTS SOME THAT THE EAST-NORTHEASTERLY FLOW COULD SPREAD STRATUS INTO THE AREA BETWEEN 00-06Z. OTHER MODELS INDICATE THAT CEILINGS WILL REMAIN IN THE LOW END VFR RANGE OVERNIGHT(4-5KT)....EVENTUALLY BECOMING SUB-VFR NEAR THE END OF THE TAF PERIOD IN ASSOCIATION WITH COLD AIR DAMMING AS THE WARM MOIST ADVECTION SPREADS EASTWARD AS THE HIGH SHIFTS OFFSHORE. LOOKING AHEAD: ADVERSE AVIATION CONDITIONS (IFR TO MVFR /LIFR CEILINGS AND RAIN) ASSOC/W A PRONOUNCED COLD AIR DAMMING WEDGE WILL PREVAIL TUESDAY AFTERNOON ... WITH SOME IMPROVEMENT IN CEILINGS POSSIBLE AT SOUTHERN TERMINALS LATE TUE NIGHT AS A WARM FRONT LIFTS NORTHWARD THROUGH THE CAROLINAS. ADVERSE AVIATION CONDITIONS ARE LIKELY TO PREVAIL THE REMAINDER OF THE WEEK. -VINCENT && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...VINCENT NEAR TERM...CBL/VINCENT SHORT TERM...KC LONG TERM...KC AVIATION...CBL/VINCENT

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