Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 240831 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 331 AM EST WED DEC 24 2014 .SYNOPSIS...A WARM FRONT WILL LIFT NORTHWARD THROUGH THE CAROLINAS AS A LOW PRESSURE SYSTEM IN THE DEEP SOUTH TRACKS INTO THE TENNESSEE VALLEY THIS AFTERNOON. AN ASSOCIATED COLD FRONT WILL SURGE EAST ACROSS THE AREA TONIGHT AS THE LOW PRESSURE SYSTEM TRACKS NORTHWARD THROUGH THE OHIO VALLEY INTO THE GREAT LAKES. && .NEAR TERM /TODAY AND TONIGHT/... AS OF 330 AM WEDNESDAY... PRECIP TODAY: WIDESPREAD RAIN WILL OVERSPREAD THE REGION THIS MORNING AS LOW-LEVEL WARM ADVECTION STRENGTHENS ATOP A SHALLOW ALBEIT PRONOUNCED COLD AIR DAMMING WEDGE IN PLACE IN THE LOWEST 1000- 1500 FT AGL. ELEVATED INSTABILITY WILL INCREASE IN MAGNITUDE AFTER 09Z AS A HIGHER THETA-E AIRMASS ADVECTS INLAND FROM THE ATLANTIC ATOP THE SHALLOWING CAD WEDGE UNDER RELATIVELY STEEP (6-7C/KM) MID- LEVEL LAPSE RATES. FCST SOUNDINGS SUGGEST MUCAPE ON THE ORDER OF 250- 750 J/KG. AS A RESULT...ELEVATED CONVECTION /ISOLD THUNDERSTORMS/ AND HEAVY RAINFALL ARE LIKELY BETWEEN 09-17Z WHEN FORCING FOR ASCENT PEAKS IN MAGNITUDE. PRECIPITATION WILL END FROM SSW-NNE BY EARLY AFTERNOON AS THE SFC-925 MB WARM FRONT LIFTS NORTHWARD INTO THE MID- ATLANTIC AND A RELATIVELY HOMOGENEOUS WARM-SECTOR SUPPLANTS THE SHALLOW CAD WEDGE PREVIOUSLY IN PLACE. PRECIP TONIGHT: PRECIPITATION MAY RE-DEVELOP IN THE FORM OF A NARROW CONVECTIVE LINE LATER THIS EVENING (ROUGHLY 00-06Z) AS THE SFC COLD FRONT SURGES EASTWARD THROUGH CENTRAL NC. CONFIDENCE IS LOWER THAN NORMAL WITH REGARD TO THE EVOLUTION OF PRECIPITATION ALONG THE COLD FRONT THIS EVENING...PARTICULARLY WITH REGARD TO PRE-FRONTAL THERMAL PROFILES /INSTABILITY/ DUE TO THE WIDE VARIETY OF MECHANISMS AND POSSIBLE INTERACTIONS DRIVING THE EVOLUTION THEREOF. BASED ON PREVIOUS EXPERIENCE WITH SIMILAR SETUPS AND THE LATEST MODEL GUIDANCE...EXPECT THE BEST POTENTIAL FOR ADDITIONAL PRECIPITATION ALONG AND EAST OF HWY 1 IN THE 01-07Z TIME FRAME. FOR EXAMPLE...THE HIGH-RES WRF-ARW SUGGESTS DRY CONDITIONS IN THE WESTERN PIEDMONT WITH A NARROW LINE OF CONVECTION DEVELOPING IN VICINITY OF THE TRIANGLE AROUND MIDNIGHT...EXITING THE COASTAL PLAIN BY 2-3 AM THU MORNING. TEMPERATURES: THE GRADUAL/ONGOING RISE IN TEMPERATURES EARLY THIS MORNING WILL GIVE WAY TO RAPIDLY RISING TEMPS (INTO THE LOWER/MID 60S) BETWEEN SUNRISE AND NOON AS THE WARM FRONT ADVANCES NORTHWARD AND THE SHALLOWING CAD WEDGE DISSIPATES ALTOGETHER. AS IS TYPICAL IN COLD AIR DAMMING REGIMES...COMPLETE WEDGE EROSION (AND HIGH TEMPS) REMAINS IN QUESTION ACROSS THE FAR NW PIEDMONT /TRIAD/. GIVEN PERSISTENT SOUTHERLY FLOW /WARM ADVECTION/ FROM EARLY AFTERNOON (WHEN PRECIP ENDS) TO THE COLD FRONTAL PASSAGE ~03Z...CAD EROSION /WARM SECTOR ESTABLISHMENT/ IN THE TRIAD APPEARS FEASIBLE. -VINCENT && .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... AS OF 255 AM WEDNESDAY... THERE MAY BE A FEW SHOWERS IN THE PROCESS OF EXITING THE FAR EASTERN ZONES CHRISTMAS MORNING... OTHERWISE EXPECT A WEST TO EAST CLEARING TRENDING IN THE WAKE OF THE EXITING COLD FRONT. ADDITIONALLY...DEEPENING SURFACE LOW LIFTING NEWD INTO SE CANADA WILL RESULT IN BREEZY CONDITIONS ON CHRISTMAS DAY...WITH WEST- NORTHWESTERLY WINDS GUSTING INTO THE UPPER TEENS TO LOWER 20S...STRONGEST DURING THE FIRST HALF OF THE DAY. WEAK CAA BEHIND THE FRONT WILL STILL ALLOW FOR SEASONABLY MILD TEMPERATURES. HIGHS IN THE MID 50S NW TO LOWER 60S SE. LOWS IN THE LOWER TO MID 30S. && .LONG TERM /SATURDAY THROUGH TUESDAY/... AS OF 255 AM WEDNESDAY... SATURDAY NIGHT INTO MONDAY...A PATTERN CHANGE WILL BEGIN TO OCCUR AS THE UPPER RIDGE OVER THE SE STATES BREAKS DOWN AND A LARGE MID/UPPER TROUGH DEVELOPS INTO THE WEST-CENTRAL THEN CENTRAL STATES. THE LEAD COLD FRONT IS EXPECTED TO PUSH INTO NC FROM THE NORTH LATE SUNDAY OR SUNDAY NIGHT. ALL BETS ARE OFF ON HOW FAR SOUTH THIS INITIAL FRONT WILL BE ABLE TO SAG INTO NC OR SC. ABOUT HALF THE GFS ENSEMBLE MEMBERS SUPPORT A STRONG ENOUGH SURFACE HIGH OVER A FAVORED GREAT LAKES LOCATION TO PUSH THE FRONT INTO SC. THIS IS NOT SUPPORTED BY THE LATEST OPERATIONAL EC AND HALF THE RELATED ENSEMBLES. THE STRENGTH OF THE SURFACE WAVE SLATED TO DEVELOP OVER THE LOWER MISSISSIPPI VALLEY AND THE SUBSEQUENT TRACK (EITHER JUST TO OUR WEST AND NORTH... OR VERY NEAR OR OVER OUR REGION) IS ALSO CURRENTLY DEBATABLE. WPC HAS SPLIT THE MIDDLE TAKING THE AVERAGE APPROACH WHICH WOULD KEEP MOST OF OUR REGION IN THE WARM SECTOR INITIALLY (UNTIL THE INITIAL WAVE OF LOW PRESSURE PASSES). THIS WOULD ENSURE ALL RAIN AND MILDER TEMPERATURES THAN IF CAD WERE TO DEVELOP PER SOME OF THE GFS MEMBERS. FOR NOW... WE WILL TREND A BIT COOLER AND WETTER... AND TOWARD THE COOLER SOLUTIONS AND GIVE IT A FEW MORE RUNS BEFORE COMMITTING EITHER WAY. THIS WOULD LEAD TO A CHANCE OF RAIN LATE SUNDAY INTO MONDAY WITH LOWS IN THE MID 30S TO MID 40S AND HIGHS IN THE MID 40S TO LOWER 60S N TO SE. A TURN TO SHARPLY COLDER WEATHER IS EXPECTED BY MID NEXT WEEK WITH LOWS BACK INTO THE 20S AND HIGHS IN THE 40S. && .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/... AS OF 200 AM WEDNESDAY... 24-HR TAF PERIOD: LIFR CONDITIONS ASSOCIATED WITH A PRONOUNCED COLD AIR DAMMING WEDGE WILL PERSIST OVER CENTRAL NORTH CAROLINA THIS MORNING AS WIDESPREAD PRECIPITATION OVERSPREADS THE REGION FROM THE SOUTH/SW. GRADUAL IMPROVEMENT TO IFR AND PERHAPS LOW-END MVFR IS EXPECTED FROM SOUTH/SE TO NORTH/NW LATE THIS MORNING INTO THIS AFTERNOON AS A WARM FRONT LIFTS NORTHWARD THROUGH CENTRAL NC... EARLIEST AT THE FAY TERMINAL AND LATEST AT THE INT/GSO TERMINALS. SOUTHERLY LOW LEVEL WIND SHEAR ALREADY PRESENT OVER THE REGION WILL STRENGTHEN AND LOWER IN ALTITUDE (FROM ~1500 FT AGL TO 500 FT AGL) BETWEEN 09-15Z AS A LOW PRESSURE SYSTEM DEEPENS WEST OF THE MOUNTAINS AND THE COLD AIR DAMMING WEDGE GRADUALLY SHALLOWS/ERODES IN ASSOC/W THE WARM FRONT PROGRESSING NORTHWARD THROUGH THE AREA. LOW LEVEL WIND SHEAR WILL ABATE BY EARLY AFTERNOON AS THE CAD WEDGE ERODES/DISSIPATES. IFR OR LOW-END MVFR CONDITIONS...RAIN...AND A SOUTHERLY BREEZE WILL PREVAIL THIS AFTERNOON AND EVENING...IN ADVANCE OF A COLD FRONT APPROACHING FROM THE WEST. VFR CONDITIONS WILL RETURN FROM WEST-EAST BETWEEN MIDNIGHT AND SUNRISE THURSDAY AS BREEZY WEST/NW WINDS ADVECT A DRIER AIRMASS INTO THE REGION IN THE WAKE OF THE COLD FRONT. LOOKING AHEAD: VFR CONDITIONS WILL PREVAIL THURSDAY INTO THE WEEKEND IN ASSOCIATION WITH HIGH PRESSURE OVER THE REGION. -VINCENT && .HYDROLOGIC DISCUSSION /TONIGHT THROUGH THURSDAY/... AS OF 210 PM TUESDAY... THERE HAVE BEEN THREE FAIRLY SIGNIFICANT RAINFALL EVENTS OVER CENTRAL NORTH CAROLINA DURING THE PAST TWO WEEKS...WITH HEAVIER RAINFALL AMOUNTS (>1 INCH TOTAL) GENERALLY FROM THE TRIANGLE AND FAYETTEVILLE AREAS EAST TO THE COAST. AS A RESULT...RELATIVE SOIL MOISTURE IS UNIFORMLY HIGH THROUGH A 200 CM DEEP COLUMN...WHICH WILL PROMOTE FASTER RUNOFF AS WELL AS A HIGHER PERCENTAGE OF RAINFALL-TO- RUNOFF FROM THE UPCOMING EVENT TONIGHT THROUGH CHRISTMAS MORNING. CURRENT QUANTITATIVE PRECIPITATION FORECASTS RANGE FROM 1.25 INCHES TO NEARLY 2 INCHES...AND HAVE BEEN TRENDING DOWNWARD WITH SUCCESSIVE MODEL RUNS. AT THIS TIME...OUR PREFERRED RAINFALL FORECAST IS FOR WIDESPREAD AMOUNTS OF LESS THAN 1.5 INCHES...WHICH WILL CAUSE MAINSTEM RIVERS TO RISE SEVERAL FEET FROM CHRISTMAS DAY INTO THE WEEKEND...BUT RIVER FORECAST POINTS WOULD CREST BELOW MINOR FLOOD STAGE. WIDESPREAD RAIN NEARER THE HIGH END OF THIS RANGE (1.75 TO 2 INCHES) WOULD LIKELY PRODUCE MINOR FLOODING ON EASTERN RIVERS... PARTICULARLY THE HAW...NEUSE...AND TAR RIVERS. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...VINCENT NEAR TERM...VINCENT SHORT TERM...BADGETT LONG TERM...BADGETT AVIATION...VINCENT HYDROLOGY...BADGETT

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