Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 200759 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 257 AM EST SAT DEC 20 2014 .SYNOPSIS...A FAST MOVING DISTURBANCE WILL TRACK EASTWARD ACROSS THE REGION TODAY. WEAK HIGH PRESSURE WILL EXTEND ACROSS CENTRAL NORTH CAROLINA SUNDAY. ANOTHER DISTURBANCE AND ASSOCIATED SURFACE LOW PRESSURE SYSTEM WILL AFFECT OUR AREA SUNDAY NIGHT INTO MONDAY. && .NEAR TERM /OVERNIGHT/... AS OF 1010 PM FRIDAY... A SHORTWAVE TROUGH PROGRESSING THROUGH THE CENTRAL AND LOWER MS RIVER VALLEY THIS EVENING WILL TRACK E/ENE ACROSS THE TN VALLEY TO THE SOUTHERN APPALACHIANS BY 12Z SAT...INDUCING WEAK CYCLOGENESIS ALONG A BAROCLINIC ZONE OFFSHORE THE SOUTHEAST COAST AS HIGH PRESSURE CONTINUES TO EXTEND SOUTH/SOUTHEASTWARD INTO THE CAROLINAS. PRECIP: THE BEST UPPER LEVEL FORCING...DPVA ASSOC/W THE APPROACHING SHORTWAVE...WILL LARGELY REMAIN WEST OF THE AREA THROUGH SUNRISE SAT...THOUGH WEAK DPVA ATTENDANT SMALL AMPLITUDE DISTURBANCES OVER THE DEEP SOUTH APPEAR LIKELY AS THEY TRACK ENE INTO THE CAROLINAS BETWEEN 06-12Z. THOUGH LOWER-LEVEL FORCING IS ABSENT OVER CENTRAL NC THIS EVENING...WEAK WARM ADVECTION WILL DEVELOP AFTER MIDNIGHT AS 10- 15 KT WESTERLY FLOW AT THE ~850 MB LEVEL BACKS TO THE SOUTHWEST IN RESPONSE TO THE APPROACHING SHORTWAVE. GIVEN THAT THE APPROACHING SHORTWAVE WILL REMAIN WEST OF THE APPALACHIANS THROUGH MOST OF THE NIGHT...WARM ADVECTION WILL BE WEAK (SHORT-LIVED AS WELL)...AND THAT THE 00Z GSO RAOB SHOWED A THOROUGHLY DRY AIRMASS IN PLACE ACROSS CENTRAL NC THIS EVENING...IT SEEMS UNLIKELY THAT SUFFICIENT FORCING AND/OR MOISTURE ADVECTION WILL OCCUR IN ORDER FOR MEASURABLE PRECIPITATION TO DEVELOP PRIOR TO SUNRISE. TEMPS: LOWS WILL RANGE FROM THE LOWER 30S IN THE NE COASTAL PLAIN TO THE MID/UPPER 30S IN THE FAR SW PIEDMONT AS THICKENING MID-LEVEL CLOUD COVER PROGRESSES INTO THE AREA FROM SW-NE. THE RELATIVE BEST CHANCE FOR MEASURABLE PRECIP (PRIOR TO 12Z) WILL BE IN THE WESTERN PIEDMONT. GIVEN THAT MEASURABLE PRECIP WILL LARGELY DEPEND UPON THE MAGNITUDE/DURATION OF LOW-LEVEL WARM ADVECTION...THE PRESENCE THEREOF (IN THIS CASE) WOULD IMPLY THERMAL PROFILES EXCLUSIVELY SUPPORTIVE OF LIQUID. -VINCENT && .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... AS OF 300 PM FRIDAY... A SOUTHERN STREAM SHORTWAVE IS EXPECTED TO ARRIVE FROM OUR SOUTHWEST ON SATURDAY MORNING. THE LAST SEVERAL NUMERICAL MODEL RUNS HAVE ALL TRENDED THIS SYSTEM TO BE DRIER...ESPECIALLY IN OUR NORTHERN COUNTIES. BOTH THE GLOBAL AND THE HIGH RESOLUTION MODELS DO THIS AND THEREFORE HAVE TRENDED BACK ON POPS AND QPF FORECASTS FOR SATURDAY WITH MAINLY CHANCES WITH SOME BRIEF LIKELIES ACROSS THE EXTREME SOUTHERN TIER DURING THE LATE MORNING/EARLY AFTERNOON. THIS ALSO SEVERELY HANDICAPS ANY THREAT OF SNOW ACROSS THE TRIAD THAT WAS POTENTIALLY BEING SHOWN BY PRIOR MODEL RUNS. FIRST...THERE MAY NOT EVEN BE PRECIPIATION AT ALL IN THIS AREA. IF PRECIPIATION DOES IN FACT OCCUR HERE...THE BEST OMEGA IS IN THE 700 MB LEVEL AND QUICKLY DIMINISHES ABOVE THAT. THUS CURRENT MODELS...INCLUDING THE NAM WHICH WAS THE MOST BULLISH ON THE SITUATION...NEARLY SATURATES IN THE 800- 600 MB LEVEL BUT LESS SO ABOVE THAT INTO THE SNOW GROWTH ZONE. INCLUDE A WARM BOUNDARY LAYER INTO THE MIX AND CHANCES ARE HIGH THAT ANY FALLING PRECIP WILL BE LIQUID. THE CONCLUDING UPSHOT OF THE DAY WILL BE AN OVERCAST DAY WITH TEMPERATURES IN THE MID 40S WITH BETTER CHANCES OF SOME VERY LIGHT RAIN IN THE SOUTH. THE SYSTEM WILL MOVE OUT TO THE EAST OVERNIGHT AND LOW TEMPERATURES ARE EXPECTED TO DROP IN TO THE LOW TO MID 30S WITH THE COLDEST TEMPS IN THE NORTHWEST PIEDMONT. SUNDAY WILL FEATURE HIGH PRESSURE BUILDING IN FROM THE NORTH AND STARTING TO MOVE INTO POSITION TO EVENTUALLY FORM A CAD WEDGE BUT INITIALLY WILL HELP AID SOME PARTIAL CLEARING EARLY SUNDAY BEFORE INCREASING CLOUDS FROM THE SOUTH TAKE OVER BY AFTERNOON. IT SHOULD BE A WARMER DAY THAN SATURDAY WITH TEMPS IN THE UPPER 40S NW TO LOWER 50S SE. INCREASING MOISTURE FROM APPROACHING SOUTHERN LOW WILL BRING DEWPOINTS UP NEAR 40 DEGREES BY THE END OF THE AFTERNOON BUT THE SURFACE HIGH WILL KEEP ANY PRECIPIATION SOUTH OF THE AREA THROUGH THE AFTERNOON. && .LONG TERM /MONDAY THROUGH FRIDAY/...
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AS OF 255 AM SATURDAY... MONDAY THROUGH WEDNESDAY: A SOUTHERN STREAM S/W DISTURBANCE WILL LIFT NORTHEASTWARD OUT FROM THE GULF COAST STATES ON SUNDAY NIGHT INTO MONDAY MORNING... SPREADING WIDESPREAD RAIN ACROSS ALL OF CENTRAL NC AS ISENTROPIC LIFT RAMPS UP. WITH A 1030 MB SURFACE HIGH STILL EXPECTED TO BE EXTENDING SOUTHWARD INTO OUR AREA (AS IT EVER SO SLOWLY SHIFTS EASTWARD) EXPECT WE WILL SEE A PRONOUNCED DAMMING EVENT DEVELOP.... WITH TEMPS FALLING INTO THE MID TO UPPER 30S MONDAY MORNING ACROSS THE NORTHERN AND NORTHWEST PIEDMONT... WITH TEMPS IN THE 40S ELSEWHERE. HOWEVER... BOTH THE GFS AND ECMWF CONTINUE TO DEPICT AN ALL RAIN EVENT ACROSS THE AREA... WITH A PRONOUNCED WARM NOES AT AROUND 4-5KFT COMBINED WITH SURFACE WETBULB TEMPS IN THE MID 30S AT WORST WHEN THE PRECIP SPREADS INTO THE AREA. THE MORE SUBSTANTIAL PRECIP WILL COME TO AN END BY EARLY TO MID AFTERNOON AS THE BEST MOIST ISENTROPIC UPGLIDE BEGINS TO WANE ALONG WITH DRIER AIR ALOFT FILTERING INTO THE AREA. STILL WE SHOULD SEE SOME LINGERING AREAS OF LIGHT RAIN AND DRIZZLE REMAINING. WITH A GOOD AREAWIDE QUARTER TO A HALF INCH OF RAIN EXPECTED WE SHOULD BE ABLE TO LOCK IN THE DAMMING AIRMASS. THUS.. HAVE LOWERED HIGH TEMPS... ESPECIALLY ACROSS THE EASTERN/SOUTHEASTERN PORTION OF CENTRAL NC. EXPECT HIGH TEMPS TO RANGE FROM THE UPPER 30S N/NW TO THE MID TO UPPER 40S E/SE. TEMPS MONDAY NIGHT/TUESDAY MORNING ARE EXPECTED TO REMAIN NEAR STEADY OR EVEN SLOWLY BEGIN TO RISE A LITTLE. THUS... WILL GO WITH LOWS RANGING FROM THE UPPER 30S TO MID 40S. A NORTHERN STREAM DISTURBANCE WILL HAVE FORMED A DEEP TROUGH BY TUESDAY MORNING WITH STACKED LOW PRESSURE OVER THE UPPER MIDWEST. BOTH THE GFS AND ECMWF ARE IN GOOD AGREEMENT IN SHOWING THE DEEP ASSOCIATED TROUGH AXIS SHIFTING EASTWARD ON TUESDAY INTO WEDNESDAY WHILE TAKING ON MORE OF A NEGATIVE TILT... WITH THE ASSOCIATED SURFACE FRONT (AND A POSSIBLE TRIPLE POINT LOW) MOVING ACROSS CENTRAL NC ON WEDNESDAY MORNING INTO THE EARLY AFTERNOON (AS IT STANDS NOW... STILL SEVERAL DAYS OUT THOUGH). QUESTIONS REMAIN AS TO WHERE A POSSIBLE TRIPLE POINT LOW MAY FORM THOUGH... AS FINER DETAILS LIKE THIS ARE HARD TO NAIL DOWN THIS FAR OUT IN THE FORECAST. HOWEVER... WITH THE POTENTIAL FOR A RETREATING CAD BOUNDARY AND STRENGTHENING LOW LEVEL WIND FIELD... WE WILL NEED TO KEEP AN EYE ON HOW THIS SYSTEM COMES TOGETHER. THIS WOULD BE A HSLC TYPE OF SYSTEM. GIVEN THE TIME OF YEAR IT IS QUITE HARD TO GET THE NEEDED INSTABILITY FOR POSSIBLE SEVERE STORMS THOUGH. AS THE EFFECTIVE FRONT APPROACHES AND MOVES THROUGH THE AREA ON WEDNESDAY MORNING INTO THE AFTERNOON WE SHOULD SEE A BAND OF RAIN/SHOWERS ALONG AND IN ADVANCE OF IT (WITH POSSIBLY A FEW THUNDERSTORMS)... WITH THINGS DRYING OUT QUICKLY BEHIND THE EFFECTIVE FRONT ON WEDNESDAY AFTERNOON. HIGHS ON TUESDAY WILL BE TRICKY AND DEPEND ON HOW MUCH THE CAD BOUNDARY RETREATS. FOR NOW WILL GO WITH HIGHS IN THE UPPER 40S NW TO AROUND 60S SE. TEMPS BY WEDNESDAY MORNING WILL NOT FALL MUCH... WITH LOWS WEDNESDAY MORNING IN THE UPPER 40S NW TO MID 50S SE/E. TEMPS ARE EXPECTED TO WARM WEDNESDAY AHEAD OF THE FRONT INTO THE UPPER 50S NW TO THE UPPER 60S E. WEDNESDAY NIGHT THROUGH THURSDAY: WE SHOULD SEE RAPID CLEARING ON WEDNESDAY NIGHT AND CONTINUING FOR THE REST OF THE WEEK... WITH A RETURN TO QUITE WEATHER. LOWS THURSDAY MORNING ARE EXPECTED TO BE IN THE 30S... WITH HIGHS THURSDAY AND FRIDAY AFTERNOONS IN THE 50S. WE COULD BE A BIT BREEZE ON THURSDAY AS MODELS ARE SHOWING THE POTENTIAL FOR SUSTAINED WINDS OUT OF THE WSW IN THE 14 TO 20 MPH RANGE... WITH MAYBE SOME GUSTS OF UP TO 25 MPH.
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&& .AVIATION /06Z SATURDAY THROUGH WEDNESDAY/... AS OF 105 AM SATURDAY... AN UPPER LEVEL DISTURBANCE ADVANCING EAST ACROSS THE DEEP SOUTH WILL PASS SOUTH OF CENTRAL NC LATER THIS MORNING THROUGH EARLY AFTERNOON. THIS WEATHER SYSTEM WILL INCREASE CLOUDINESS ALONG WITH PATCHES OF LIGHT RAIN OVER OUR REGION BY DAYBREAK. EXPECT CEILINGS TO LOWER TO THE 4000-6000FT LAYER WITH SCATTERED PATCHES OF STRATOCU WITH CEILINGS 1500-2500FT POSSIBLE BY LATE MORNING THROUGH THE AFTERNOON...MAINLY SOUTH OF HIGHWAY 64. THIS THREAT FOR LOWER CEILINGS WILL AFFECT THE KFAY TERMINAL. SURFACE WINDS WILL BECOME NELY WITH SUSTAINED WINDS AOB 10KTS. WEAK HIGH PRESSURE WILL BUILD INTO CENTRAL NC FROM NORTH TONIGHT AND SUNDAY...MAINTAINING MOSTLY VFR CONDITIONS. A STRONGER UPPER LEVEL DISTURBANCE AND ASSOCIATED SURFACE LOW PRESSURE SYSTEM WILL BRING A HIGH PROBABILITY OF ADVERSE AVIATION CONDITIONS TO CENTRAL NC SUNDAY NIGHT INTO MONDAY. WIDESPREAD MVFR/IFR CEILINGS AND AREAS OF RAIN ARE EXPECTED. THESE CONDITIONS WILL SPREAD NORTH INTO SOUTHERN SECTIONS OF CENTRAL NC SHORTLY AFTER SUNSET SUNDAY THEN CONTINUE NORTHWARD SUNDAY NIGHT. A DECENT TO HIGH THREAT FOR MVFR CEILINGS WILL LINGER MONDAY NIGHT INTO TUESDAY AS THE LOW LEVEL AIR MASS REMAINS MOIST. A STRONG COLD FRONT WILL APPROACH TUESDAY NIGHT AND CROSS THE REGION WEDNESDAY. GUSTY SLY WINDS ARE EXPECTED AHEAD OF THE FRONT TUESDAY NIGHT ALONG WITH HEAVY SHOWERS AND POSSIBLY A THUNDERSTORM OR TWO. THE FRONT WILL CROSS THE AREA WEDNESDAY WITH BLUSTERY WESTERLY WINDS EXPECTED IN ITS WAKE. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...WSS NEAR TERM...VINCENT SHORT TERM...ELLIS LONG TERM...BSD AVIATION...WSS

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