Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 282347 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 746 PM EDT SUN SEP 28 2014 .SYNOPSIS...HIGH PRESSURE WILL EXTEND ACROSS THE MIDDLE ATLANTIC STATES THROUGH TONIGHT. A WEAK AREA OF LOW PRESSURE WILL DEVELOP AND TRACK ACROSS THE GULF COAST MONDAY...THEN OFF THE SOUTHEAST COAST MONDAY NIGHT AND TUESDAY. && .NEAR TERM /THROUGH TONIGHT/... AS OF 315 PM SUNDAY... REMAINDER OF THE AFTERNOON INTO TONIGHT... A WEAK SFC RIDGE ORIENTATED SW-NE ACROSS THE REGION WILL MAINTAIN ITS INFLUENCE ACROSS CENTRAL NC THROUGH TONIGHT. ALOFT...WEAK UPPER RIDGE HAS WEAKENED AND DRIFTED EAST IN RESPONSE TO A PAIR OF VORTICES MOVING EAST...ONE ACROSS THE MID MS VALLEY INTO THE WESTERN LAKES...AND THE OTHER OVER THE NW-NORTH CENTRAL GULF COAST. THE LATER FEATURE WILL HAVE AN IMPACT ON OUR SENSIBLE WEATHER LATER TONIGHT AND MORE SO MONDAY AS LIFTS NEWD. MID-HIGH LEVEL MOISTURE WILL CONTINUE TO ADVECT INTO THE CAROLINAS...LEADING TO MORE EXTENSIVE HIGH AND MID LEVEL CLOUDS...ESPECIALLY WEST OF HIGHWAY 1. ISENTROPIC LIFT IN THE LOWEST 10K FT WEAK TO NON-EXISTENT THROUGH DAYBREAK SO APPEARS THAT ANY PRECIP THAT OCCURS OVERNIGHT SHOULD BE LIMITED TO SPRINKLES IF THAT. EXTENSIVE CLOUDINESS OVER THE WEST WILL RESULT IN MILDER MIN TEMPS COMPARED TO THE NORTHERN COASTAL PLAIN WHERE FAIR-PARTLY CLOUDY SKIES THIS EVENING MAY ALLOW TEMPS TO TUMBLE SHORTLY AFTER SUNSET..THEN STABILIZE AFTER MIDNIGHT AS CLOUDS THICKEN. MIN TEMPS UPPER 50S TO NEAR 60 NE TO THE LOW-MID 60S SOUTH-SW. && .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 /00Z MONDAY THROUGH FRIDAY/...
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AS OF 745 PM SUNDAY... 24 HOUR TAF PERIOD: VFR CONDITIONS SHOULD PREVAIL THROUGH MUCH OF THE TAF PERIOD AT ALL SITES ALTHOUGH THERE IS A POSSIBILITY OF SOME MVFR VISIBILITY RESTRICTIONS. A SHROUD OF HIGH CLOUDS THIS EVENING SHOULD HELP TO DETER THE FOG FORMATION OVERNIGHT. WILL NOT COVER IN THE TAFS AT THIS TIME. WINDS WILL BE LARGELY CALM OVERNIGHT. AS A LOW PRESSURE SYSTEM APPROACHES FROM THE SOUTHWEST...CHANCES FOR RAIN BEGIN TO INCREASE FROM WEST TO EAST. SOME SPRINKLES MAY EVOLVE AFTER 6Z OR SO BUT ANY LIGHT RAIN SHOULD HOLD OFF UNTIL CLOSER TO DAYBREAK. THE EXPECTATION FOR MONDAY IS THAT CLOUD BASES WILL REMAIN VERY HIGH AND RAIN WILL BE LIGHT TO POCKETS OF MODERATE INTENSITY AT BEST. IT WILL TAKE A LONG TIME FOR THE LOW LEVELS OF THE ATMOSPHERE TO MOISTEN UP AND CLOUD DECKS COULD VERY WELL STAY VFR THROUGH THE END OF THE TAF PERIOD. WINDS WILL BE LIGHT AND VARIABLE. LONG TERM: THE LOW LEVELS OF THE ATMOSPHERE WILL EVENTUALLY MOISTEN UP LATE MONDAY INTO TUESDAY AND COULD BRING A PERIOD OF SUB-VFR CONDITIONS TO THE AREA BUT SHOULD RETURN TO VFR LATE TUESDAY. A STRONG SYSTEM WILL AFFECT THE AREA FRIDAY NIGHT WITH THE POTENTIAL FOR SOME ADVERSE AVIATION CONDITIONS INTO SATURDAY.
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&& .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...MWS NEAR TERM...WSS SHORT TERM...WSS LONG TERM...DJF AVIATION...ELLIS

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