Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 211924 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 224 PM EST SUN DEC 21 2014 .SYNOPSIS...
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HIGH PRESSURE TO THE NORTH WILL SET UP A COLD AIR DAMMING EVENT WITH PRECIPIATION CHANCES INCREASING TONIGHT AND INTO MONDAY AS A SURFACE LOW MOVES UP THE SOUTHEAST COAST.
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&& .NEAR TERM /THROUGH MONDAY NIGHT/...
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AS OF 220 PM SUNDAY... HIGH PRESSURE OVER THE MID ATLANTIC STATES IS SLOWLY SHIFTING EASTWARD THIS AFTERNOON AND INTO A FAVORABLE POSITION FOR A HYBRID COLD AIR DAMMING EVENT TO BEGIN. THIS IS KEEPING MOISTURE PENNED UP SOUTH OF THE AREA TODAY BUT A SOUTHERN STREAM SHORTWAVE WILL BEGIN TO CREATE SOME TROUGHING ALONG THE COAST OVERNIGHT TONIGHT INTO MONDAY WHICH WILL HELP TO SHARPEN UP THE WEDGE FRONT ACROSS CENTRAL NC AND SET THE STAGE FOR A WET COUPLE OF DAYS. FOR THE REST OF TODAY EXPECT LESS CLOUD COVER EAST OF HIGHWAY ONE WITH LINGERING MVFR CEILINGS IN THE WEST. THIS HAS BEEN TRYING TO BURN OFF OVER THE PAST SEVERAL HOURS BUT SOME PLACES ARE STILL UNDER GREY SKIES. THIS IS CREATING A LOT OF DIFFERENTIAL HEATING ACROSS THE CWA AND ANY LOCALES IN THE CLEARING HAVE TEMPERATURES RISING ABOVE FORECASTED HIGHS AND THOSE UNDER THE CLOUD COVER ARE STILL BELOW FORECASTED HIGHS. THE END RESULT WILL BE PLUS OR MINUS 50 DEGREES DEPENDING ON LOCATION. WINDS ARE MAINTAINING A NORTHEASTERLY COMPONENT AND WILL CONTINUE TO DO SO WITH SPEED AROUND 5 KTS. TONIGHT...MOISTURE WILL BEGIN TO INCREASE FROM THE SOUTH AIDED BY ISENTROPIC LIFT INCREASING OVER TOP OF THE WEDGE THAT WILL BEGIN TO BUILD IN THIS EVENING...AND THE RIGHT ENTRANCE REGION OF AN UPPER JET THAT IS PROGGED TO BEGIN TO MOVE OVER CENTRAL NC DURING THE LATE NIGHT HOURS. HIGH RESOLUTION MODELS HAVE PRECIPITATION BEGINNING IN THE SOUTHERN COUNTIES AFTER 00Z AND SPREADING NORTHWARD THROUGH THE CWA BY ABOUT 4Z OR SO. THE ONSET OF PRECIPIATION WILL ALSO MARK THE BEGINNING OF MVFR CEILINGS. LOW TEMPERATURES WILL RANGE FROM THE MID 30S NORTH TO LOW 40S SOUTH. MONDAY AND MONDAY NIGHT: RAIN IS EXPECTED TO PERSIST THROUGH THE DAY ON MONDAY AS THE SURFACE LOW MOVES NORTHWARD JUST OFF THE NC COAST. LOW CEILINGS AT IFR LEVELS ARE EXPECTED THROUGHOUT THE DAY. WHILE RAIN IS EXPECTED TO BE CONTINUOUS...THE QPF AMOUNTS WITH THIS SYSTEM ARE FAIRLY LOW. ONLY EXPECT A TOTAL OF A QUARTER TO A HALF OF AN INCH OF RAIN. WITH THE WEDGE LOCKED IN TO THE WEST AND THE COASTAL TROUGH TO THE EAST...THERE SHOULD BE A FAIRY DECENT GRADIENT FROM NORTHWEST TO SOUTHEAST IN THE HIGH TEMPERATURE SPREAD ON MONDAY. HIGHS IN THE NORTHWEST PIEDMONT WILL STRUGGLE TO GET TO 40 DEGREES WHEREAS HIGHS CLOSER TO 50 WILL BE COMMON IN THE SOUTHEAST. FOR THE MOST PART PRECIPIATION IS EXPECTED TO END AFTER 00Z TUESDAY BUT CONTINUED MOISTURE IN THE AREA WILL LEND ITSELF TO CONTINUING DRIZZLE THROUGH THE NIGHT ON MONDAY. THIS WET AND COOL PERIOD WILL ALSO LEND ITSELF TO PERIODS OF PATCHY FOG WITH THE MOST LIKELY TIMES BEFORE SUNRISE ON TUESDAY. LOWS IN THE MID 30S TO LOWER 40S.
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&& .SHORT TERM /MONDAY AND MONDAY NIGHT/... AS OF 325 AM SUNDAY... MONDAY...BEST LIFT ASSOCIATED WITH THE SOUTHERN STREAM S/W WILL AFFECT OUR REGION MONDAY MORNING THEN LIFT NEWD OUT OF OUR AREA MONDAY AFTERNOON. THUS...WILL ADVERTISE HIGHEST POPS IN THE MORNING WITH DECREASING POPS IN THE AFTERNOON. AGAIN MODEL CONSENSUS HAS DECREASED EXPECTED RAINFALL AMOUNTS COMPARED TO 24 HOURS AGO BUT STILL EXPECT AROUND A QUARTER OF AN INCH. THE WIDESPREAD RAIN EARLY IN THE DAY WILL AID TO LOCK IN THE CAD AIR MASS AND ASSOCIATED LOW CLOUDS. THIS WILL RESULT IN MAX TEMPS JUST 5-8 DEGREES WARMER THAN EXPECTED MIN TEMPS. MAX TEMPS NEAR 40 NW TO NEAR 50 FAR SE. MONDAY NIGHT...CAD AIR MASS EXPECTED TO PERSIST MAINTAINING EXTENSIVE CLOUDINESS WITH AREAS OF DRIZZLE OR SPOTTY LIGHT RAIN. TEMPS USUALLY DO NOT DISPLAY MUCH DIURNAL CHANGE IN THIS TYPE OF AIR MASS SO MIN TEMPS EXPECTED TO RANGE FROM THE MID 30S NW TO THE LOW- MID 40S SE. && .LONG TERM /TUESDAY THROUGH SATURDAY/... AS OF 215 AM SUNDAY... ...WARM... WET AND RATHER WINDY SYSTEM TO AFFECT OUR REGION TUESDAY NIGHT THROUGH CHRISTMAS EVE... THEN WINDY AND COOLER CHRISTMAS DAY... THERE IS HIGH CONFIDENCE OF A WARM... WET AND WINDY SYSTEM WILL AFFECT OUR REGION MID WEEK. MODELS AND ENSEMBLES AGREE IN GENERAL IN THAT A THE MAIN SURFACE STORM TRACK WILL BE FROM THE GULF OF MEXICO NORTHWARD THROUGH THE TENNESSEE AND OHIO VALLEY REGIONS TUE NIGHT INTO WEDNESDAY NIGHT. THE OPERATIONAL GFS IS SLOWER/A BIT WEAKER WITH THE MAIN SURFACE WAVE... DEPICTING A 997 MB SURFACE LOW OVER KY 18Z/WED... WHILE THE AVERAGE OF THE ENSEMBLES SUGGEST AROUND A 992 LOW OVER OR NEAR NW OHIO 12Z/WED. REGARDLESS... WITH THE STORM HEADING UP THE WEST SIDE OF THE APPALACHIANS... OUR REGION WILL HAVE TO DEAL WITH RESIDUAL COLD AIR DAMMING... A RETREATING WEDGE/WARM/COASTAL FRONT... AND THEN THE MAIN COLD FRONT. TIMING OF THESE WILL BE CRITICAL TO THE SENSIBLE WEATHER FORECASTS. THIS FAR OUT... THESE DETAILS WILL HAVE TO BE REFINED AS THE EVENT EVOLVES. AT THIS POINT WE WILL MAINTAIN CONTINUITY FROM OUR PREVIOUS FORECASTS AND BLEND IN THE LATEST ENSEMBLE MEANS TO GIVE IT OUR BEST SHOT AT EACH OF THESE FEATURES. ONE THING FOR SURE... CONFIDENCE IS 100 PERCENT IN ALL RAIN. TUESDAY AND TUESDAY NIGHT... LINGERING COLD AIR DAMMING IS EXPECTED TO BE IN PLACE OVER A GOOD PORTION OF THE PIEDMONT DAMMING REGION 12Z/TUESDAY. AN INITIAL WEAK SURFACE WAVE SHOULD BE TRACKING OFF THE DELMARVA COAST WITH A TRAILING COASTAL FRONT INTO SE GEORGIA. THIS COASTAL FRONT APPEARS THAT IT WILL HAVE A DIFFICULT TIME COMING INLAND INITIALLY GIVEN THAT THE MAIN STORM TRACK AND DYNAMICS WILL BE LIFTING NORTH (WEST OF THE MOUNTAINS) INSTEAD OF COMING EAST OR NORTHEAST ACROSS THE MOUNTAINS. THE PRESSURE GRADIENT WILL BE LACKING TUESDAY. HOWEVER... THE WAA PATTERN WILL INCREASE LATER TUESDAY INTO TUESDAY NIGHT AS THE SURFACE WAVE STRENGTHENS OVER THE TENNESSEE VALLEY AND LIFTS TOWARD OHIO BY 12Z/WED. WAA RAINS WILL BE AIDED BY WARM FRONTAL LIFT FROM THE SOUTHEAST LATE TUESDAY NIGHT INTO EARLY WEDNESDAY. SOME OF THE LATEST GUIDANCE SUGGESTS THE HEAVIEST RAINS MAY FALL OVER THE WESTERN PIEDMONT INTO THE MOUNTAINS ALONG AND NEAR THE RETREATING WARM/COASTAL FRONT. IT IS STILL DIFFICULT TO FORECAST EXACTLY WHERE THE WARM FRONT WILL BE LOCATED 12Z/WED... BUT WHEN CLIMATOLOGY IS APPLIED TO THE GIVEN STORM TRACK AND STRENGTH ALONG WITH THE LINGERING CAD (RETREATING SURFACE HIGH OF 1030 MB OFF NEW ENGLAND)... THE WARM FRONT MOST LIKELY WILL BE VERY NEAR THE SE PIEDMONT FROM CHARLOTTE TO RALEIGH EARLY IN THE DAY WED. THE FRONT SHOULD LIFT INTO VIRGINIA DURING THE AFTERNOON. THIS WILL LIKELY LEAD TO A LULL IN THE WARM FRONTAL RAINS AS THEY LIFT INTO VIRGINIA WEDNESDAY AFTERNOON. 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. SENSIBLE WEATHER TUESDAY THROUGH WEDNESDAY... COOL AND CLOUDY TUESDAY WITH SOME LIGHT DRIZZLE. THEN A CHANCE OF RAIN AGAIN IN TEH AFTERNOON IN THE SW. HIGHS IN THE MID 40S TO MID 50S (PROBABLY NOT UNTIL TUESDAY EVENING). PERIODS OF RAIN... SOME HEAVY TUESDAY NIGHT INTO WEDNESDAY MORNING. RAIN ENDING FROM THE SOUTH BY AFTERNOON. THEN SHOWERS AND A SLIGHT CHANCE OF THUNDERSTORMS AGAIN IN THE MID TO LATE AFTERNOON (NW)... LATE AFTERNOON AND EVENING ELSEWHERE. BECOMING WINDY AND WARMER FROM THE SOUTH TUESDAY NIGHT INTO WEDNESDAY (NW ZONES LATEST TO SEE WARMING). TEMPS RISING LATE WITH READINGS MID 50S TO MID 60S BY 12Z/WED NW TO SE. HIGHS WEDNESDAY IN THE MID 60S TO LOWER 70S. SHOWERS TAPER OFF QUICKLY FROM THE WEST WEDNESDAY NIGHT. CLOUDY WITH LOWS IN THE 40S TO LOWER 50S. THURSDAY THROUGH SATURDAY... THE PRESSURE GRADIENT WILL REMAIN TIGHT THURSDAY WITH A GUSTY W-NW WIND AT 15-25 MPH. HIGHS GENERALLY IN THE 50S WITH PARTLY TO MOSTLY SUNNY SKIES. FRIDAY SHOULD BE DRY WITH ANOTHER COLD FRONT EXPECTED TO AFFECT THE REGION BY LATE FRIDAY NIGHT AND SATURDAY WITH A CHANCE OF RAIN SHOWERS. LOWS 35-40. HIGHS 55-62. && .AVIATION /18Z SUNDAY THROUGH FRIDAY/... AS OF 130 PM SUNDAY... FORECAST IS EASIER TO MANAGE TODAY AS THE BEST CONDITIONS WILL BE THIS AFTERNOON AND THEN FOLLOWED BY A HIGH CONFIDENCE FORECAST OF CONDITIONS DETERIORATING AFTER DARK AND INTO THE OVERNIGHT HOURS DOWN TO FIRST MVFR AND THEN IFR LEVELS WHERE THEY WILL REMAIN FOR THE REMAINDER OF THE TAF PERIOD. ADVERSE CONDITIONS ARE ASSOCIATED WITH A LOW PRESSURE SYSTEM DEVELOPING OFF OF THE SOUTHEAST COAST THAT WILL BRING AN INFLUX OF MOISTURE FROM THE SOUTH. THIS WILL BE IN THE FORM OF RAIN AS TEMPERATURES WILL REMAIN ABOVE FREEZING THROUGHOUT THE EVENT. WHILE THERE MAY BE POCKETS OF SOME MVFR VISIBILITIES...IFR CONDITIONS WILL PRESENT IN THE FORM OF LOW STRATUS. PRECIPITATION WILL START JUST AFTER 00Z IN THE SOUTH AND PUSH NORTHWARD UNTIL ALL SITES ARE UNDER THE PRECIP SHIELD JUST AFTER 4Z GIVE OR TAKE. THE ONSET OF PRECIPITATION SHOULD ALSO MARK THE ONSET OF MVFR CONDITIONS AND THEN LATER ON DOWN TO IFR NEAR DAYBREAK MONDAY. WINDS WILL BE 5-10 KTS OUT OF AN EAST NORTHEASTERLY DIRECTION FOR MUCH OF THE TAF PERIOD. CONDITIONS ARE NOT EXPECTED TO RECOVER BEFORE 18Z MONDAY. LONG TERM: LOW CEILINGS ARE EXPECTED TO REMAIN WELL INTO MIDWEEK AS CONTINUOUS UNSETTLED WEATHER AFFECTS THE AREA THROUGH WEDNESDAY NIGHT. THIS WILL BE CHARACTERIZED BY PERIODS OF RAIN...FOG AND POSSIBLY A THUNDERSTORM. CONDITIONS SHOULD RETURN TO VFR FOR CHRISTMAS DAY WITH SOME AFTERNOON GUSTY WINDS POSSIBLE. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...ELLIS NEAR TERM...ELLIS SHORT TERM...CBL LONG TERM...WSS AVIATION...ELLIS

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