Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 220949 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 449 AM EST MON DEC 22 2014 .SYNOPSIS...
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A COLD AIR DAMMING RIDGE WILL REMAIN LOCKED IN PLACE EAST OF THE APPALACHIANS THROUGH TUESDAY. A WARM FRONT WILL LIFT NORTHWARD THROUGH THE REGION LATE TUESDAY NIGHT AND WEDNESDAY AS A DEVELOPING LOW PRESSURE SYSTEM STRENGTHENS WEST OF THE MOUNTAINS.
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&& .NEAR TERM /TODAY THROUGH TUESDAY/... AS OF 345 AM MONDAY... BACKED LOW-LEVEL FLOW /WARM ADVECTION/ ASSOCIATED WITH APPROACHING SHORTWAVE TROUGHS /DPVA/ IN SW FLOW ALOFT HAS RESULTED IN WIDESPREAD RAIN OVER THE REGION AS OF 08Z THIS MORNING. ELEVATED CONVECTION (HEAVIER RAINFALL) WILL BE MOST LIKELY BETWEEN 09-15Z THIS MORNING ACROSS THE TRIANGLE AND NE COASTAL PLAIN WHERE PARCELS LAUNCHED ATOP THE PRONOUNCED COLD AIR DAMMING WEDGE WILL ENCOUNTER MARGINAL ELEVATED INSTABILITY AND MORE FAVORABLE MID-LEVEL MOISTURE. EXPECT THE HEAVIEST PRECIPITATION TO PROGRESS N/NE OF CENTRAL NC BY MID TO LATE MORNING AS SHORTWAVE ENERGY PROGRESSES NORTHEAST...H85 FLOW VEERS TO THE WEST...AND A DRIER MID-LEVEL AIRMASS ADVECTS ATOP THE COLD AIR DAMMING WEDGE LOCKED IN PLACE OVER THE REGION. LIGHT PRECIPITATION AND DRIZZLE ARE EXPECTED TO LINGER THROUGH 15Z ELSEWHERE IN ASSOC/W CONTINUED 925 MB WARM ADVECTION AND A SATURATED AIRMASS IN THE LOWEST 3-4 KFT...THOUGH AMOUNTS WILL RANGE FROM A TRACE TO A HUNDREDTHS OF AN INCH BY THAT TIME. ASIDE FROM PERIODIC DRIZZLE...EXPECT LITTLE CHANCE FOR MEASURABLE PRECIP THIS AFTERNOON THROUGH MIDNIGHT WITH FORCING LIMITED TO WEAK 925 MB WARM ADVECTION UNDER A DRY (AND TEMPORARILY SUBSIDENT) MID-LEVEL AIRMASS. EXPECT VERY LITTLE DIURNAL VARIATION IN TEMPERATURES GIVEN A STRONG COLD AIR DAMMING WEDGE IN PLACE...WITH HIGHS THIS AFTERNOON ONLY A FEW DEGREES WARMER THAN LOWS TONIGHT. ADDITIONAL SHORTWAVE ENERGY IN SW FLOW ALOFT IS PROGGED TO TRACK NORTHEAST ACROSS WESTERN PORTIONS OF THE STATE OVERNIGHT...AND THIS IS THE BASIS FOR AN INCREASED CHANCE FOR RAIN AFTER MIDNIGHT... PRIMARILY WEST OF HWY 1. PRECIP ON TUESDAY WILL DEPEND UPON THE TIMING/TRACK OF SHORTWAVE ENERGY IN SW FLOW ALOFT...AND THE SUBTLE INFLUENCE THESE FEATURES WILL IMPART UPON LOW LEVEL HEIGHT/WIND FIELDS. AS A RESULT...CONFIDENCE IS LOWER THAN NORMAL WITH REGARD TO THE TIMING/AREAL EXTENT OF PRECIPITATION ON TUE...LET ALONE PRECIP AMOUNTS. AT THIS TIME WILL INDICATE A 40-60% CHANCE OF RAIN THROUGHOUT THE DAY...HIGHEST IN THE WESTERN PIEDMONT. EXPECT TEMPERATURES TO LARGELY REMAIN STEADY DURING THE DAY TUE...THOUGH PERHAPS BEGINNING TO RISE IN THE FAR SE COASTAL PLAIN (I.E. SAMPSON COUNTY) BY SUNSET. -VINCENT && .SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/... AS OF 235 AM MONDAY... ...WARM... WET... AND RATHER WINDY SYSTEM TO AFFECT OUR REGION TUESDAY NIGHT THROUGH CHRISTMAS EVE... THEN WINDY AND COOLER CHRISTMAS DAY... MODELS AND ENSEMBLES DEPICT WITH HIGH CONFIDENCE THAT A WARM... WET AND WINDY SYSTEM WILL AFFECT OUR REGION MID WEEK. THE MAIN SURFACE STORM TRACK WILL BE FROM THE GULF OF MEXICO NORTHWARD THROUGH THE TENNESSEE AND OHIO VALLEY REGIONS TUESDAY NIGHT INTO WEDNESDAY. SINCE THE STORM WILL BE HEADING UP TO THE WEST OF THE APPALACHIANS OUR REGION WILL HAVE TO DEAL WITH RESIDUAL COLD AIR DAMMING WHICH APPEARS TO BE EVEN MORE LOCKED IN IN THE LATEST MODEL RUNS INTO TUESDAY NIGHT (AND EVEN WEDNESDAY MORNING IN THE NW PIEDMONT). THE MAIN COLD FRONT IS SLATED TO FOLLOW THE WARM FRONTAL PASSAGE WEDNESDAY AFTERNOON AND NIGHT WITH SOME LINGERING TIMING DIFFERENCES IN THE OPERATIONAL MODELS. TIMING OF THESE WILL BE CRITICAL TO THE SENSIBLE WEATHER FORECASTS. WE WILL MAINTAIN CONTINUITY FROM OUR PREVIOUS FORECASTS AND BLEND WITH THE LATEST ENSEMBLE MEANS FROM THE GFS/EC TO GIVE IT OUR BEST SHOT AT THE TIMING/STRENGTH OF THESE FEATURES. TUESDAY NIGHT... RAIN EXPECTED TO BECOME WIDESPREAD FROM THE SOUTH AND WEST AS THE WARM/WEDGE FRONT GRADUALLY LIFTS NORTH INTO THE REGION. LINGERING COLD AIR DAMMING IS EXPECTED TO BE IN PLACE OVER A GOOD PORTION OF THE PIEDMONT DAMMING REGION THROUGH 06Z/WEDNESDAY... THEN GRADUALLY GIVE WAY TO THE WARM FRONT BETWEEN 06Z-12Z WEDNESDAY AS THE MAIN STORM LIFTS UP THROUGH THE TENNESSEE VALLEY. RAINFALL MAY BECOME HEAVY AIDED BY STRONG WAA LIFT UP AND OVER THE WARM FRONT. LOWS WILL LIKELY BE EARLY IN THE NIGHT WITH RISING TEMPERATURES IN ALL BUT THE FAR NW CORNER OVERNIGHT. TEMPS SHOULD BEGIN THE EVENING IN THE LOWER 40S NW TO 50S SE... THEN RISE INTO THE 60S SOUTH AND EAST BY 12Z/WED. WEDNESDAY... THE WARM FRONT SHOULD LIFT INTO VIRGINIA. THIS WILL LIKELY LEAD TO A LULL IN THE WARM FRONTAL RAINS AS THEY LIFT INTO VIRGINIA WEDNESDAY AFTERNOON. HIGHS SHOULD RISE INTO THE 60S WEST AND LOWER 70S EAST. WEDNESDAY PM... THE MAIN COLD FRONT SHOULD ARRIVE BETWEEN 00Z/06Z THURSDAY (WEDNESDAY NIGHT)... ACCOMPANIED BY ADDITIONAL SHOWERS AND POSSIBLY A FEW THUNDERSTORMS (IF THE LOW LEVELS CAN DESTABILIZE ENOUGH... WHICH IS IN DOUBT - GIVEN THE TIME OF YEAR. HOWEVER... SURFACE DEW POINTS WEDNESDAY AFTERNOON IN THE WARM SECTOR SHOULD REACH 60 OR EVEN 65 SE. BREEZY TO WINDY SW FLOW AT 10-25 MPH CAN BE EXPECTED WITH TEMPS INTO THE 65-72 RANGE. THIS WOULD STILL ONLY YIELD MUCAPES OF 100 TO 200 J/KG. IN ADDITION... THE STRONGEST LOW LEVEL JET IS EXPECTED TO PUSH NORTHWARD INTO VA/MD BY EARLY WEDNESDAY AFTERNOON ALONG THE RETREATING WARM FRONT. WITH THE MAIN DYNAMICS PASSING OVER THE GREAT LAKES... THESE FACTORS WILL GREATLY LIMIT ANY SEVERE POTENTIAL WITH THIS STORM FOR CENTRAL NC. STORM TOTAL QPF OF 1 TO 1.5 INCHES IS EXPECTED WITH THIS EVENT ENDING WEDNESDAY EVENING/NIGHT AS THE COLD FRONT PUSHES EAST OF THE REGION. THIS WILL INTRODUCE A MUCH DRIER... COOLER AND WINDY CHRISTMAS DAY. && .LONG TERM /THURSDAY THROUGH SUNDAY/... AS OF 225 AM MONDAY... THE MAIN STORM AND COLD FRONT WILL SWEEP WELL OFFSHORE EARLY THURSDAY. BREEZY TO WINDY CONDITIONS ON CHRISTMAS DAY WILL GRADUALLY SUBSIDE AS A MILD PACIFIC ORIGIN HIGH WILL BUILD IN LATE IN THE DAY. DRY AND SEASONABLY MILD CONDITIONS ARE EXPECTED AFTER THE WESTERLY WINDS AT 15-25 MPH DIMINISH LATER THURSDAY AND FRIDAY. LOWS IN THE 30S AND HIGHS IN THE 50S ARE EXPECTED. MODEL SPREAD REMAINS LARGE LATE FRIDAY THROUGH THE WEEKEND. THE GFS/EC ENSEMBLE MEANS WERE BLENDED TO TRY TO CAPTURE A GENERAL FORECAST GIVEN THE SPREAD IN THE MODELS. THIS YIELDS A COLD FRONTAL PASSAGE SATURDAY WITH A WEAK WAVE POTENTIAL TO FOLLOW. THIS WOULD GIVE AN INCREASE IN A CHANCE OF RAIN SUNDAY. P-TYPE IS NOT EXPECTED TO BE A CONCERN AT THIS POINT... BUT AN EVEN COLDER AIR MASS IS EXPECTED TO BE DRIVEN SE INTO OUR LATITUDE EARLY TO MID NEXT WEEK (LIKELY AFTER THE SAID WAVE OF LOW PRESSURE SLIDES WELL OFFSHORE). LOWS IN THE 30S AND HIGHS IN THE 40S SUNDAY WILL BE REPLACED BY LOWS THE 20S AND HIGHS IN THE 40S MONDAY WITH DRIER CONDITIONS. && .AVIATION /06Z MONDAY THROUGH FRIDAY/... AS OF 200 AM MONDAY... 24-HR TAF PERIOD: CONDITIONS WILL DETERIORATE TO IFR/LIFR THIS MORNING AS RAIN OVERSPREADS THE REGION. THOUGH RAIN WILL LARGELY END BY NOON...IFR/LIFR CEILINGS AND OCCASIONAL DRIZZLE WILL PERSIST THE REMAINDER OF THE TAF PERIOD IN ASSOCIATION WITH A PRONOUNCED COLD AIR DAMMING WEDGE LOCKED FIRMLY IN PLACE. LOOKING AHEAD: ADVERSE AVIATION CONDITIONS WILL PERSIST THROUGH THE REMAINDER OF THE WEEK AS A POWERFUL STORM SYSTEM AFFECTS THE EASTERN CONUS MID/LATE WEEK. -VINCENT && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...VINCENT NEAR TERM...VINCENT SHORT TERM...BADGETT LONG TERM...BADGETT AVIATION...VINCENT

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