Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 211956 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 255 PM EST SUN DEC 21 2014 .SYNOPSIS...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. && .NEAR TERM /THROUGH MONDAY NIGHT/... 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. && .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... AS OF 300 PM SUNDAY... TUESDAY: MID-LEVEL DRY AIR AND THE ABSENCE OF DISCERNIBLE FORCING...ASIDE FROM WEAK SOUTHERLY UPGLIDE...DOWNSTREAM OF THE DEEPENING TROUGH WILL KEEP MEASURABLE RAIN CHANCES LOW ACROSS CENTRAL NC DURING MUCH OF THE DAY ON TUESDAY. DESPITE A LACK OF PRECIP...SHROUD OF LOW CLOUDS WILL HELP TO KEEP THE LINGERING COLD AIR WEDGE LARGELY IN PLACE ACROSS CENTRAL NC. MEASURABLE RAIN CHANCES WILL RETURN BY THE LATE AFTERNOON/EVENING WITH THE RESURGENCE OF WARM MOIST ADVECTION AND LOW-LEVEL CONVERGENCE ALONG THE NORTHWARD RETREATING WEDGE FRONT. TEMPERATURES TUESDAY DURING THE DAY WILL REMAIN THE 40S THROUGHOUT MUCH OF THE DAY...THE EXCEPTION WILL BE ACROSS THE FAR SE ZONES WHERE NEARBY WEDGE/WARM FRONT COULD ALLOW TEMPERATURES TO WARM INTO THE LOWER 50S LATE IN THE DAY. TUESDAY NIGHT THROUGH WEDNESDAY NIGHT: SOGGY...BREEZY...AND POSSIBLY STORMY CONDITIONS... AHEAD OF THE AMPLIFYING UPSTREAM LONGWAVE TROUGH AND ATTENDANT SFC COLD FRONT...DEEP GULF MOISTURE FEED WILL TRANSPORT ANOMALOUSLY HIGH PWATS OF 1.5-1.7" INTO THE REGION...WHICH WOULD RANK IN THE 99TH PERCENTILE(HIGHEST OBSERVED PWAT DURING THE MONTH OF DEC AT KGSO BASED ON THE RADIOSONDE DATABASE WHICH DATE BACKS TO 1948 IS 1.59"- 12/21/1991). STRENGTHENING RIGHT ENTRANCE JET REGION COUPLED WITH THIS STRONG MOISTURE FLUX CONVERGENCE WILL RESULT IN CATEGORICAL POPS AND A WIDESPREAD SOAKING RAIN OF 1-2"...HEAVY AT TIMES TUESDAY NIGHT AND INTO CHRISTMAS EVE MORNING. ONCE THE WARM FRONT LIFTS NORTHWARD INTO THE VIRGINIA...THERE WILL LIKELY BE A LULL IN PRECIP UNTIL THE ARRIVAL OF THE COLD FRONT AND ATTENDANT BAND OF SHOWERS AND POSSIBLY EMBEDDED THUNDER THROUGH THE AREA BETWEEN 00-06Z THURSDAY...WHICH IS A BIT SLOWER THAN YESTERDAYS TIMING. SEVERE POTENTIAL: EVALUATING SEVERE POTENTIAL IN A LOW CAPE-HIGH SHEAR ENVIRONMENT IS ALWAYS DIFFICULT...EVEN AT CLOSER TIME SCALES OF 6-12 HOURS...MUCH LESS AT THE CURRENT TIME SCALE OF 3 TO 4 DAYS. THE LULL IN PRECIP DURING MUCH OF THE DAYTIME HOURS...MAY ALLOW FOR SOME MODEST HEATING...ESPECIALLY FROM THE US 1 CORRIDOR EASTWARD...WHICH COULD LEAD TO BETTER DESTABILIZATION THAN MODEL CURRENTLY SHOW(100-200J/KG MUCAPE). WEAK LAPSE RATES ALOFT OF 5.0- 5.5 C/KM ALONG WITH THE MAIN DYNAMICS PASSING OVER THE GREAT LAKES...WILL LIMIT WIDESPREAD SEVERE POTENTIAL...BUT GIVEN IMPRESSIVE DEEP LAYER SHEAR CANNOT RULE OUT ISOLATED SEVERE STORM AT THIS TIME. TEMPERATURES VERY CHALLENGING WITH HIGH BUST POTENTIAL...DEPENDENT ON EVOLUTION/TIMING/LOCATION OF THE RETREATING WEDGE FRONT INTO THE CLIMATOLOGICALLY FAVORED AREA ACROSS THE FAR NW PIEDMONT TUESDAY NIGHT AND INTO THE DAY ON WEDNESDAY. EXPECT TEMPERATURES TO STEADILY WARM AFTER MIDNIGHT TUESDAY NIGHT...WITH THE EXCEPTION BEING ACROSS THE NW PIEDMONT...WHERE TEMPS COULD HOLD NEARLY STEADY. LOWS RANGING FROM LOWER 40S NW TO MID 50S SE. WARM SECTOR SHOULD OVERSPREAD MUCH OF THE AREA BY WEDNESDAY AFTERNOON...WARMING INTO THE 60S ACROSS THE PIEDMONT...AND POSSIBLY LOWER 70S ACROSS THE SANDHILLS/SOUTHERN COASTAL PLAIN. RAPID CLEARING AND COOL AIR ADVECTION WILL COMMENCE CHRISTMAS EVE EVENING/NIGHT WITH LOWS CHRISTMAS MORNING IN THE UPPER 30S NW TO LOWER/MID 40S SE. && .LONG TERM /THURSDAY THROUGH SUNDAY/... AS OF 255 PM SUNDAY... DEEPENING SURFACE LOW LIFTING NEWD INTO SE CANADA WILL RESULT IN BREEZY CONDITIONS ON CHRISTMAS DAY. OTHERWISE DRY WITH SEASONABLY MILD TEMPERATURES CONTINUING INTO FRIDAY AS HIGH PRESSURE BUILDS IN FROM THE NORTHERN GULF. MODEL SPREAD BEGINS TO INCREASE DRAMATICALLY LATE FRIDAY THROUGH THE WEEKEND...WITH THE EC MUCH DEEPER WITH THE NEXT MID/UPPER LEVEL TROUGH...RESULTING IN YET ANOTHER WET AND UNSETTLED PERIOD NEXT WEEKEND. MEANWHILE...THE LESS AMPLIFIED GFS INDICATES QUASI-ZONAL FLOW ACROSS SOUTHEAST US WITH DRY CONDITIONS THROUGH THE WEEKEND. WILL INDICATE SLIGHT CHANCE POPS UNTIL BETTER AGREEMENT IS REACHED. && .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...CBL AVIATION...ELLIS

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