Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 220748 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 235 AM EST MON DEC 22 2014 .SYNOPSIS...HIGH PRESSURE OVER THE NORTHEAST WILL WEDGE IN TO THE AREA THROUGH TUESDAY...AS A LOW PRESSURE SYSTEM MOVES ALONG THE COAST. ANOTHER STORM SYSTEM WILL APPROACH FROM THE SOUTHWEST TUESDAY NIGHT AND WEDNESDAY. && .NEAR TERM /THROUGH MONDAY NIGHT/... AS OF 1055 PM SUNDAY... TONIGHT: A PERTURBED SOUTHWESTERLY UPPER JET...WITH A SERIES OF WELL- DEFINED IMPULSES ON WV VAPOR IMAGERY FROM THE WESTERN GOM TO THE MID-ATLANTIC COAST AND WHICH INCLUDES A 250 MB 150 KT JET STREAK OBSERVED AT KWAL...WILL PROMOTE AN ACCELERATION OF THE UNDERLYING LOW LEVEL FLOW ACROSS THE CAROLINAS TONIGHT. AN ASSOCIATED 925-850 MB WARM FRONT...ANALYZED AT 00Z JUST INLAND OF THE GULF COAST TO THE SAVANNAH BASIN...WILL CONSEQUENTLY RETREAT NORTHWARD; ASSUME AN INCREASINGLY SW TO NE ORIENTATION; AND BISECT CENTRAL NC BY 12Z... PER A WELL AGREED UPON CONSENSUS OF NWP GUIDANCE. THE LIFT AND ASSOCIATED MOISTURE TRANSPORT - STRONGEST IN AN AXIS BOUNDED ROUGHLY BY I-95 AND US HWY 1 - WILL CAUSE RAIN TO INCREASE IN COVERAGE AND INTENSITY AS IT SPREADS/DEVELOPS NORTHWARD FROM SC. INDEED HOURLY RAINFALL AMOUNTS OVER SC HAVE INCREASED FROM A FEW HUNDREDTHS OR LESS FOR MUCH OF THE AFTERNOON AND EVENING...TO A TENTH TO .15 DURING THE PAST COUPLE OF HOURS. THE LATEST NMM AND RAP...AND 21Z SREF MEAN SUPPORT THIS IDEA OF INCREASING RAINFALL RATES AND AMOUNTS DEVELOPING NORTH INTO OUR AREA...WITH AN AXIS OF A QUARTER TO HALF INCH PROBABLE CENTERED SQUARELY OVER CENTRAL NC THROUGH 12Z. LOCALLY HIGHER AMOUNTS WILL BE POSSIBLE WERE EMBEDDED HEAVIER RAIN OCCURS OWING TO POCKETS OF WEAK ELEVATED INSTABILITY CHARACTERIZED BY MUCAPE VALUES OF UP TO A COUPLE OF HUNDRED J/KG. ASIDE FROM OVER THE FAR NE PIEDMONT AND NORTHERN COASTAL PLAIN... WHERE LOWS IN THE MID 30S HAVE ALREADY BEEN ATTAINED FROM A BRIEF PERIOD OF RELATIVE CLEAR AND RADIATIONAL COOLING EARLY THIS EVENING...TEMPERATURES WILL HOLD STEADY OR EVEN RISE A DEGREE OR TWO WITH THICKENING CLOUD COVER...BEFORE FALLING VIA EVAPORATIONAL COOLING AS THE RAIN OVERSPREADS THE AREA AND CAUSES TEMPERATURES TO TREND TO SURFACE WET BULB TEMPERATURES IN THE MIDDLE 30S TO LOWER 40S. -MWS && .SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/...
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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.
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&& .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 /00Z MONDAY THROUGH FRIDAY/... AS OF 710 PM SUNDAY... THERE IS HIGH CONFIDENCE THAT AVIATION CONDITIONS WILL DETERIORATE TONIGHT AS A LOW PRESSURE SYSTEM BEGINS TO DEVELOP OFF THE SOUTHEAST COAST. WHILE A FEW PATCHES OF LIGHT RAIN WILL BE POSSIBLE IN THE NEXT FEW HOURS... EXPECT THE LIGHT RAIN CURRENTLY OVER SC TO EXPAND AND SPREAD INTO NC AFTER 06Z...WITH CEILINGS EVENTUALLY LOWERING TO MVFR AND IFR...FIRST AT KFAY/KGSO/KINT BY 06-08Z AND THEN KRDU/KRWI BY 09Z. ONCE IFR CEILINGS DEVELOP...FORECAST SOUNDING SHOW VERY LITTLE IMPROVEMENT...IF ANY...DURING THE DAY ON MONDAY. THE RAIN WILL TRANSITION TO JUST DRIZZLE AS THE DAY PROGRESSES...BUT POOR AVIATION CONDITIONS WILL PERSIST THROUGH THE END OF THE TAF PERIOD. LONG TERM: POOR CONDITIONS WITH LOW CEILINGS/VSBYS AND PERIODS OF RAIN WILL CONTINUE THROUGH TUESDAY AND INTO WEDNESDAY. A COLD FRONT WILL CROSS THE AREA ON WEDNESDAY...BRINGING STRONG WINDS AND A CHANCE OF A FEW THUNDERSTORMS. CONDITIONS SHOULD RETURN TO VFR FOR CHRISTMAS DAY WITH SOME AFTERNOON GUSTY WINDS POSSIBLE. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...SEC NEAR TERM...MWS/ELLIS SHORT TERM...BADGETT LONG TERM...BADGETT AVIATION...BLS

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