Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 290518 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 120 AM EDT MON SEP 29 2014 .SYNOPSIS...A WEAK AREA OF LOW PRESSURE WILL DEVELOP OVER THE NORTHEAST GULF TODAY... CROSS NORTHERN FLORIDA TONIGHT... AND THEN TRACK NORTHEASTWARD OFF THE SOUTHEAST COAST TUESDAY. WEAK HIGH PRESSURE WILL BUILD OVER THE AREA WEDNESDAY. && .NEAR TERM /THROUGH TONIGHT/... AS OF 1000 PM SUNDAY... MID/HIGH LEVEL MOISTURE AND ASSOCIATED CLOUDINESS WILL CONTINUE TO STREAM INTO THE REGION FROM THE SOUTH/WEST OVERNIGHT AHEAD OF A APPROACHING MID LEVEL SHORTWAVE. THIS SHORTWAVE WILL INDUCE CYCLOGENESIS ALONG THE GULF COAST...WITH THIS LOW (AND BEST PRECIP CHANCES) PROGGED TO TRACK WELL SOUTH OF CENTRAL NC THROUGH MONDAY NIGHT. IN RESPONSE TO SOME UPPER LEVEL FORCING...AN AREA OF LIGHT RAIN HAS DEVELOPED AND PERSISTED ALONG THE INTERSTATE 85 CORRIDOR FROM ATLANTA TO CHARLOTTE...AND THE LATEST HRRR HAS A FAIRLY GOOD HANDLE ON THIS. THIS AREA OF PRECIP IS EXPECTED TO SLOWLY SPREAD INTO THE SOUTHEASTERN/WESTERN PORTIONS OF THE FORECAST AREA SHORTLY AFTER MIDNIGHT...HOWEVER MUCH OF THE FORECAST AREA WILL LIKELY REMAIN PRECIP FREE THROUGH DAYBREAK. REGARDLESS... ANY PRECIP AMOUNTS WILL BE LIGHT AS THE AREA IS REMOVED FROM THE BEST FORCING. WITH REGARDS TO TEMPS...EXTENSIVE CLOUDINESS OVER THE SOUTH/WEST WILL RESULT IN MILDER OVERNIGHT LOWS (LOW TO MID 60S) COMPARED TO THE NORTHERN COASTAL PLAIN WHERE LESS CLOUD COVER (AT LEAST EARLY ON IN THE NIGHT) MAY ALLOW TEMPS TO FALL INTO THE UPPER 50S TO NEAR 60 DEGREES BEFORE THE THICKENING CLOUD COVER MOVES EAST. && .SHORT TERM /MONDAY AND MONDAY NIGHT/... AS OF 315 PM SUNDAY... MONDAY...THE SURFACE LOW ASSOCIATED WITH THE GULF COAST/SE U.S. UPPER LEVEL SYSTEM IS PROJECTED TO TRACK ALONG THE GULF COAST MONDAY AND DRIFT OFF THE GA COAST MONDAY NIGHT. DUE TO THE FAR SOUTHERN TRACK OF THE SYSTEM...MOST OF THE LIFT TO GENERATE WIDESPREAD MODERATE TO HEAVY PRECIP WILL BE FARTHER SOUTH...WHILE PRECIP OVER CENTRAL NC WILL BE MAINLY GENERATED FROM LIFTING ALOFT...YIELDING TO LIGHTER PRECIP AMOUNTS. THUS WHAT WAS LOOKING TO BE A SIGNIFICANT RAIN EVENT FOR PORTIONS OF CENTRAL NC A FEW DAYS AGO IS NOW LOOKING MUCH WEAKER. EXPECT PATCHES OF PRECIP TO BREAK OUT IN THE MORNING...BECOMING LIKELY GENERALLY SOUTH OF HIGHWAY 64 BY MIDDAY. HAVE DECREASED EXPECTED RAINFALL AMOUNTS BASED ON LATEST GFS/HPC GUIDANCE. THIS YIELDS STORM TOTALS RANGING FROM LESS THAN A QUARTER OF AN INCH NORTH OF HIGHWAY 64...AND A LITTLE MORE THAN A HALF INCH ACROSS THE SOUTH. SINCE PRECIP EXPECT TO BE LIGHT/SPOTTY...IT IS LOOKING LESS LIKELY THAT A HYBRID/IN-SITU CAD WILL SET-UP. THUS...TEMPS HAVE BEEN ADJUSTED UPWARD A FEW DEGREES ACROSS THE NORTHERN PIEDMONT BUT STILL ONE TO TWO CATEGORIES BELOW MOS. IF PRECIP FAILS TO MATERIALIZE...MAX TEMPS IN THE TRIAD AND TRIANGLE AREAS MAY END UP BEING 3-4 DEGREES WARMER. CURRENTLY...WILL HAVE MAX TEMPS WITHIN A DEGREE OR TWO OF 70 EXCEPT OVER TEH FAR NORTHERN COASTAL PLAIN WHERE LOW-MID 70S MAY OCCUR. MONDAY NIGHT...PRECIP STILL EXPECTED TO GRADUALLY DIMINISH FROM THE WEST-NW AS THE UPPER LEVEL SYSTEM CROSSES AND EXITS THE REGION. RAINFALL COVERAGE SHOULD DIMINISH OVER THE SE COUNTIES WELL AFTER MIDNIGHT. MIN TEMPS IN THE UPPER 50S TO LOWER 60S. && .LONG TERM /TUESDAY THROUGH SUNDAY/... AS OF 155 PM SUNDAY... FOR THE PERIOD TUESDAY THROUGH WEDNESDAY...AS THE GUIDANCE TREND HAS CONTINUED AND APPEARED TO ACCELERATE OVER THE LAST COUPLE OF MODEL RUNS OR SO...ALTHOUGH AN UPPER TROUGH REMAINS IN PLACE TUESDAY MORNING...SURFACE LOW PRESSURE IS SUPPRESSED WELL SOUTH AND THEN HEADS FROM NEAR THE SOUTH CAROLINA COAST OUT TO SEA. THIS OCCURS AS A MID-LEVEL LOW MOVES FROM THE LOWER GREAT LAKES INTO THE MID- ATLANTIC...AND AN EXTENSION OF THE MID-LEVEL TROUGH SHARPENS SLIGHTLY AND MOVES OFFSHORE. THE NAM IS SLIGHTLY SLOWER THAN THE GFS...AND WITH BETTER LOW-LEVEL MOISTURE FROM ABOUT KIXA TO KFAY AND EAST...WOULD HANG ON TO LOWER CLOUDS THERE TUESDAY INTO THE AFTERNOON WITH A SMALL CHANCE OF RAIN IN THE MORNING. OTHERWISE... THE NAM AND THE GFS ARE BASICALLY SUBSIDENT FOR THIS PERIOD...WITH RELATIVELY LOW K INDICES AND CONVERGENCE ALOFT...AND VIRTUALLY NO QPF. OVERNIGHT TUESDAY INTO EARLY WEDNESDAY...A WEAK MID-LEVEL SHORTWAVE IS FORECAST TO MOVE THROUGH CENTRAL NORTH CAROLINA ALONG WITH AN INCREASE IN POTENTIAL VORTICITY ON THE 1.5PVU SURFACE...BUT BOTH THE NAM AND GFS ONLY SUGGEST A PERIOD OF SOME HIGH CLOUDS WITH THESE FEATURES LATE TUESDAY NIGHT AND ESPECIALLY WEDNESDAY MORNING INTO THE EARLY AFTERNOON. ASIDE FROM A SMALL CHANCE OF RAIN MAINLY TUESDAY MORNING ALONG AND EAST OF INTERSTATE 95 IN DEFERENCE TO THE NAM...WILL HAVE A DRY FORECAST TUESDAY THROUGH WEDNESDAY. IF THE GFS IS CORRECT...THE SKY FORECAST TUESDAY WILL BE MORE OPTIMISTIC THAN THIS FORECAST WILL SHOW ESPECIALLY EAST OF U.S. 1...WITH AN AVERAGE PARTLY SUNNY DAY EXPECTED WEDNESDAY. THE MAV AND MET MOS GUIDANCE ARE VERY CLOSE FOR HIGHS TUESDAY AND ARE IN BASIC AGREEMENT WITH EXPECTATIONS FROM 1000-850MB THICKNESSES. THESE VALUES WOULD REPRESENT A SIGNIFICANT INCREASE FROM THE PREVIOUS FORECAST. FOR THIS FORECAST WILL BE SOMEWHAT CONSERVATIVE ALTHOUGH CERTAINLY TREND HIGHER...NOT QUITE AS HIGH AS THE MOS GUIDANCE SHOWS...ESSENTIALLY A BLEND OF ALL OF THE GUIDANCE PACKAGES AVAILABLE BOTH COOL AND WARM FOR HIGHS IN THE MID TO UPPER 70S. OVERNIGHT LOWS 56 TO 61 TUESDAY NIGHT...THEN HIGHS 75 TO 80 WEDNESDAY...COOLEST NORTHEAST WHERE THE CONSENSUS OF GFS AND NAM UPPER-LEVEL MOISTURE FIELDS SUGGESTS ANY HIGH CLOUDS SHOULD ARRIVE DURING THE MORNING AND EXTEND INTO THE AFTERNOON KEEPING SOLAR INSOLATION LOWER COMPARED TO THE REST OF CENTRAL NORTH CAROLINA. FOR THE PERIOD WEDNESDAY NIGHT THROUGH SUNDAY...MID-LEVEL LOW PRESSURE MOVES OFF OF THE MID-ATLANTIC COAST WITH INCREASING HEIGHTS ALOFT BRIEFLY FOR THURSDAY. DURING THIS TIME...BOTH THE GFS AND THE ECMWF PROVIDE FOR WEAK QPF IN CENTRAL NORTH CAROLINA...AND WHILE COARSE SOUNDINGS FROM BOTH MODELS SUGGEST LIMITED INSTABILITY AND SOME AVAILABLE LOW-LEVEL MOISTURE...LIFT SHOULD BE WEAK UNDER BROAD HIGH PRESSURE. THE ECMWF DOES FORECAST A WEAK 700MB WAVE MOVING THROUGH...SO IF ALL PARAMETERS COME TOGETHER AN ISOLATED SHOWER OR TWO COULD OCCUR...BUT WILL MAINTAIN A DRY FORECAST FOR NOW FOR WEDNESDAY NIGHT INTO THURSDAY. FOR THE END OF THE WEEK...THE ECMWF IS LESS AMPLIFIED WITH LOW PRESSURE TO FOLLOW THE RIDGE OVER THE GREAT LAKES...WHICH RESULTS IN THE SURFACE FRONT MOVING FASTER TOWARD CENTRAL NORTH CAROLINA BY VERY LATE FRIDAY AFTERNOON COMPARED TO THE GFS. THE OVERALL PATTERN IS SIMILAR...THOUGH...PUSHING THE FRONT THROUGH CENTRAL NORTH CAROLINA OVERNIGHT FRIDAY INTO EARLY SATURDAY...THEN COOL HIGH PRESSURE BUILDING IN BEHIND IT. WHILE COARSE MODEL SOUNDINGS ARE NOT VERY UNSTABLE...THE STRENGTH OF THE MID-LEVEL WAVE FORECAST BY BOTH MODELS...IN COMBINATION WITH THE STRENGTH OF THE FRONT AND THE JET AXIS ALOFT MOVING TOWARD CENTRAL NORTH CAROLINA...SUGGEST THE POTENTIAL FOR THUNDER. A SMALL CHANCE OF A SHOWER OR THUNDERSTORM TOWARD THE YADKIN RIVER LATE FRIDAY AFTERNOON...FOLLOWED BY A SOLID CHANCE OF SHOWERS AND THUNDERSTORMS FRIDAY NIGHT...POSSIBLY A SHOWER LINGERING INTO EARLY SATURDAY EAST DEPENDING ON THE FRONTAL TIMING. AN ALTERNATIVE COULD BE FASTER TIMING OF BOTH THE BEGINNING AND END OF PRECIPITATION IF THE GFS TRENDS CONTINUE. DRY AND COOL SATURDAY AFTERNOON INTO SUNDAY...WITH THE POTENTIAL FOR SOME OVERNIGHT LOWS SATURDAY NIGHT TO APPROACH... OR EVEN FALL BELOW...50 DEGREES ESPECIALLY WEST AND NORTH OF THE TRIANGLE WHERE 1000-850MB THICKNESSES...GRANTED OUT TO THE END OF THE SIXTH DAY...WOULD SUGGEST AT LEAST A FEW 40S. && .AVIATION /06Z MONDAY THROUGH FRIDAY/... AS OF 120 AM MONDAY... VFR CONDITIONS WILL DOMINATE FOR THE NEXT 24 HOURS AT CENTRAL NC TAF SITES... WITH A FEW BRIEF EXCEPTIONS. A THICK DECK OF MID CLOUDS WILL CONTINUE TO OVERSPREAD THE REGION THIS MORNING... WITH CIGS EXPECTED TO LOWER BELOW 5 000 FT AGL BY MID MORNING (GSO/INT) OR THE NOON HOUR (RDU/RWI/FAY) ASSOCIATED WITH APPROACH AND PASSAGE OF A WEAK LOW-MID LEVEL TROUGH. THESE LOWERING CIGS WILL COINCIDE WITH AREAS OF LIGHT RAIN THAT WILL EXPAND OVER THE AREA FROM SW TO NE... SHIFTING EASTWARD OVER CENTRAL NC THROUGH TODAY WHILE DECREASING IN COVERAGE TO BECOME VERY LIGHT/PATCHY. BRIEF MVFR VSBYS ARE POSSIBLE IN THIS LIGHT RAIN... MAINLY NEAR GSO/INT... BUT OVERALL VFR VSBYS SHOULD STILL PREVAIL TODAY INTO TONIGHT. WINDS WILL BE LIGHT... MAINLY CALM THROUGH DAYBREAK THEN LIGHT/VARIABLE UNDER 6 KTS TODAY THROUGH TONIGHT. LOOKING BEYOND 06Z EARLY TUE MORNING... ONCE THE VEIL OF MID/HIGH CLOUDS EXITS TO THE EAST THIS EVENING LEAVING MOSTLY CLEAR SKIES... WITH WINDS STAYING VERY LIGHT... CONDITIONS ARE RIPE FOR POSSIBLE SHALLOW LIFR STRATUS/FOG BETWEEN 07Z AND 12Z TUE MORNING... HOWEVER UNCERTAINTY IS HIGH BASED ON DIFFERING COMPUTER MODEL SOLUTIONS. IF IT OCCURS... VFR CONDITIONS SHOULD RETURN BY MID MORNING TUE. MVFR FOG IS POSSIBLE JUST BEFORE AND AROUND SUNRISE WED MORNING UNDER MOSTLY CLEAR SKIES WITH LIGHT WINDS. A STRONG STORM SYSTEM WILL MOVE IN FROM THE WEST FRI... BRINGING A CHANCE OF SUB-VFR CONDITIONS AND RISING SHOWER CHANCES STARTING FRI. -GIH && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...HARTFIELD NEAR TERM...KRD SHORT TERM...WSS LONG TERM...DJF AVIATION...HARTFIELD

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