Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS62 KRAH 242041 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 335 PM EST WED DEC 24 2014 .SYNOPSIS...A WARM FRONT WILL LIFT SLOWLY NORTHWEST THROUGH THE INTERIOR CAROLINAS THROUGH THIS EVENING... AS A DEEPENING LOW PRESSURE SYSTEM TRACKS FROM THE OHIO VALLEY NORTHWARD INTO THE GREAT LAKES. A COLD FRONT WILL PUSH EAST ACROSS OUR AREA TONIGHT. HIGH PRESSURE WILL BUILD IN FROM THE SOUTHWEST FOR CHRISTMAS DAY THROUGH SATURDAY. && .NEAR TERM /THROUGH TONIGHT/... AS OF 305 PM WEDNESDAY... MOST OF THE HEAVIER PRECIP WE SAW THIS MORNING HAS SHIFTED TO THE EAST WITH THE WARM CONVEYOR BELT/LOW-LEVEL JET. MEANWHILE...THE WEDGE AND COASTAL WARM FRONTS...WHICH MADE A STRONG PUSH INLAND EARLY THIS MORNING HAVE MOVED VERY LITTLE IN THE PAST FEW HOURS. THE WEDGE FRONT STRETCHES FROM MONROE TO ASHEBORO TO ROXBORO...WHILE THE COASTAL FRONT IS CLOSER TO LAURINBURG-SMITHFIELD-TARBORO. BOTH SHOULD BEGIN TO RETREAT INLAND MORE AGGRESSIVELY THIS AFTERNOON AS THE PRECIP COMES TO AN END AND STRONGER PRESSURE FALLS BEGIN AHEAD OF THE APPROACHING UPPER TROUGH AND SYNOPTIC COLD FRONT. THE SEVERE THREAT IS DECREASING OVER THE COASTAL PLAIN AS THE FORCING DEPARTS THE AREA....SO THE BIGGER QUESTION NOW WILL BE WHETHER OR NOT THERE IS RENEWED DEVELOPMENT ALONG THE COLD FRONT. MOISTURE RETURN AND WARMING WITH THE RETREATING WARM FRONT(S) MAY ALLOW FOR SOME WEAK DESTABILIZATION AHEAD OF THE FRONT. THE NAM SHOWS MORE INSTABILITY THAN THE GFS...UP TO 400 J/KG MLCAPE IN THE EAST ON THE NAM THIS EVENING. GIVEN THE MEAGER LAPSE RATES AND LACK OF ADDITIONAL WARMING TODAY...THE NAM MAY BE OVERDONE. THERE ARE ALREADY SOME SIGNS OF SHOWERS NEAR THE COLD FRONT OVER NORTHERN GEORGIA/ALABAMA...THOUGH THE CHARACTER APPEARS MORE JET DRIVEN THAN VIA LOW-LEVEL CONVERGENCE. HOWEVER...WITH TIME...SHOWERS MAY DEVELOP AND EXPAND ALONG THE FRONT AS IT ENCOUNTERS THE SLIGHTLY MORE UNSTABLE AIRMASS OVER CENTRAL/EASTERN NC...WHICH THE CAMS WEAKLY HINT AT. IF ANY DEEPER SHOWERS/STORMS WERE TO DEVELOP...STRONG UNIDIRECTIONAL DEEP LAYER SHEAR WOULD SUPPORT A WIND THREAT...BUT THIS DOESNT SEEM LIKELY AT THE MOMENT. THE COLD FRONT CROSS WILL THE AREA BETWEEN ROUGHLY 03Z AND 09Z...WITH SIGNIFICANT DRYING IN THE LOW-LEVELS AND AN END TO ANY PRECIP. THERE IS STILL PLENTY OF MID/HIGH LEVEL MOISTURE STREAMING SOUTHWEST TO NORTHEAST JUST AHEAD OF THE UPPER TROUGH...SO SOME OF THIS CLOUD COVER MAY LINGER INTO THURSDAY MORNING AND LIMIT SOME OF THE COOLING BEHIND THE FRONT. LOWS SHOULD RANGE FROM THE MID 40S WEST TO MID 50S EAST. && .SHORT TERM /FRIDAY AND FRIDAY NIGHT/... AS OF 305 PM WEDNESDAY... AS THE COLD FRONT EXITS THE AREA...HIGH PRESSURE WILL BUILD IN FROM THE GULF COAST REGION. GIVEN THE SOURCE OF THE AIRMASS AND WESTERLY FLOW...HIGHS SHOULD BE SLIGHTLY ABOVE NORMAL IN THE MID TO UPPER 50S. WINDS WITHIN THE MIXED LAYER CAP OUT AT AROUND 25-30MPH MIDDAY...SO THERE SHOULD BE SOME GUSTS INTO THE LOWER 20S EARLIER IN THE DAY. OTHERWISE...QUIET WEATHER WILL CONTINUE ON THROUGH THURSDAY NIGHT AS HIGH PRESSURE BUILDS OVERHEAD AND LOWS DIP INTO THE LOW TO MID 30S. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... AS OF 335 PM WEDNESDAY... FOR FRI/FRI NIGHT: CALM AND MOSTLY CLEAR AS SURFACE HIGH PRESSURE DRIFTS OVERHEAD... AND MID LEVEL RIDGING BUILDS ALOFT OVER AND JUST OFF THE SOUTHEAST STATES. THE MID LEVEL AND SURFACE RIDGES WILL SHIFT EAST LATE FRI INTO FRI NIGHT. AS A RESULT OF STRENGTHENING UPPER LEVEL WINDS FROM THE SW INTO THE MIDATLANTIC REGION... HIGH THIN CLOUDS WILL SPREAD IN FRI EVENING/NIGHT. IN ADDITION... INCREASING RETURN FLOW ON THE WEST SIDE OF THE EXITING LOW LEVEL RIDGE WILL BRING A CHANCE OF FOG AND/OR STRATUS LATE FRI NIGHT AS SW WINDS INCREASE IN THE 925-850 MB LAYER. LOW LEVEL THICKNESSES START OUT CLOSE TO NORMAL... ALTHOUGH MUCH OF THIS WARMTH WILL BE CONTAINED BELOW THE SUBSIDENCE INVERSION JUST OFF THE SURFACE. REGARDLESS... GIVEN THE MILD SOURCE REGION OF THE AIR MASS... EXPECT HIGHS ABOUT A CATEGORY ABOVE NORMAL... AND LOWS NEAR TO JUST BELOW NORMAL WITH MINIMAL CLOUD COVER AND LIGHT WINDS. FOR SAT-SUN: AS THE SURFACE HIGH SHIFTS FURTHER OFFSHORE SAT... THE FRONTAL ZONE TO OUR SOUTH IS EXPECTED TO START MOVING NORTHWARD... PUSHING INTO THE NC PIEDMONT BY SUN. THE GFS/ECMWF BEGIN TO SPREAD PRECIP INTO NC FROM THE SW LATE SAT NIGHT BUT ESPECIALLY SUN... A FUNCTION OF THE STRENGTHENING SW FLOW IN THE 850-500 MB LAYER FROM THE NW GULF RIDING UP AND ALONG THE SURFACE FRONTAL ZONE. WITH GOOD MODEL AGREEMENT... WILL SPREAD IN GOOD CHANCE POPS FROM THE SW STARTING EARLY SUN MORNING... AND CONTINUING THROUGH SUN AND SUN NIGHT... AS WEAK MID LEVEL VORTICITY AND A SURFACE LOW TRACK UP ALONG THE FRONT ACROSS WRN AND NRN NC. HIGHS IN THE UPPER 50S TO LOWER 60S BOTH DAYS... LIKELY A LITTLE COOLER SUN AS THE RAIN ARRIVES. LOWS IN THE 40S SAT NIGHT AND MID 40S TO AROUND 50 SUN NIGHT. FOR MON-WED: EXPECT A DROP IN TEMPS AND AT LEAST A COUPLE OF ROUNDS OF LIGHT RAIN DURING THIS PERIOD. THE GFS/ECMWF TAKE THE FRONT BACK SOUTHWARD IN A BACKDOOR FASHION MON... AND THE FRONT SHOULD SETTLE JUST SOUTH OF THE CWA MON NIGHT... AS A PORTION OF EXPANSIVE HIGH PRESSURE CENTERED OVER THE NRN HIGH PLAINS EXTENDS INTO NC FROM THE NORTH. WE MAINTAIN A FAIRLY FLAT SW MID LEVEL FLOW FROM TX TO THE CAROLINAS THROUGH MID WEEK... AS POSITIVELY TILTED LONGWAVE TROUGHING DIGS FROM THE UPPER MIDWEST TOWARD THE DESERT SOUTHWEST. IT APPEARS LIKELY THAT WE`LL KEEP AN OVERRUNNING SW FLOW AT 850 MB UP AND OVER THE SURFACE FRONTAL ZONE... SO WE SHOULD KEEP A COOL AND FAIRLY CLOUDY AND STABLE AIR MASS OVER CENTRAL NC. IT`S DIFFICULT TO TRY TO TIME INDIVIDUAL WEAK PERTURBATIONS IN THIS SORT OF PATTERN THIS FAR OUT IN TIME... SO WILL NEED TO KEEP IN A CHANCE OF RAIN THROUGH THE PERIOD... ALTHOUGH WE SHOULD SEE THE BEST CHANCES ON MON (WITH A MORE PROMINENT WAVE PASSAGE)... AND PERHAPS EARLY WED. EXPECT EARLY-DAY HIGHS MON IN THE MID 50S TO LOW 60S... THEN HIGHS SHOULD DROP TO THE 40S FOR TUE/WED. -GIH && .AVIATION /18Z WEDNESDAY THROUGH SUNDAY/... AS OF 1210 PM WEDNESDAY... PRIMARY AVIATION CONCERNS THIS PERIOD: IFR/LIFR CONDITIONS THROUGH THIS EVENING... AND LOW LEVEL WIND SHEAR POTENTIAL THROUGH THIS AFTERNOON. PERIODS OF POOR AVIATION CONDITIONS WILL DOMINATE THROUGH THIS EVENING. A WARM FRONT ORIENTED ROUGHLY NE TO SW THROUGH CENTRAL NC WILL PUSH SLOWLY WNW TODAY THROUGH THIS EVENING... BEFORE A COLD FRONT SWEEPS IN FROM THE WEST FROM LATE EVENING THROUGH THE OVERNIGHT HOURS. THE WARM FRONT HAS ALREADY PUSHED WEST OF FAY/RWI... WHERE SURFACE WINDS ARE MAINLY FROM THE SSW... AND THE FRONT SHOULD MOVE THROUGH RDU THIS AFTERNOON. AT THESE LOCATIONS (RDU/FAY/RWI)... VSBYS/CIGS WILL WAVER BETWEEN IFR/LIFR AND MVFR THROUGH MIDNIGHT... WITH HIGH UNCERTAINTY AS TO WHICH CATEGORY WILL DOMINATE. AT INT/GSO... THERE IS A GOOD CHANCE THE WARM FRONT WILL NOT REACH THESE SITES... SO EXPECT THESE IFR/LIFR CONDITIONS TO DOMINATE NEARLY CONTINUOUSLY THROUGH MID-LATE EVENING. STRONG WINDS FROM THE SSW AT 30-50 KTS IN THE 800-1600 FT LAYER WILL BRING A RISK OF LOW LEVEL WIND SHEAR THROUGH THIS AFTERNOON... WITH THE HIGHEST LLWS POTENTIAL AT RDU WHERE THE VECTOR WIND DIFFERENCE BETWEEN THE SURFACE AND AROUND 1000 FT AGL WILL BE GREATEST. COLD FRONT PASSAGE THIS EVENING INTO THE OVERNIGHT HOURS WILL MEAN A RAPID W-TO-E TREND OF CIGS FROM MAINLY IFR/LIFR TO VFR... MOST LIKELY AT INT/GSO BETWEEN 02Z AND 04Z AND AT RDU/FAY/RWI BETWEEN 04Z AND 07Z... WITH A SHIFT OF WINDS TO WSW THEN WNW. VFR CONDITIONS WILL THEN DOMINATE FROM LATE TONIGHT THROUGH THE END OF THE TAF VALID PERIOD... AS HIGH PRESSURE BUILDS IN FROM THE SW. LOOKING BEYOND 18Z THU... VFR CONDITIONS ARE EXPECTED TO HOLD FROM CHRISTMAS AFTERNOON INTO SUNDAY... ALTHOUGH SOME GROUND FOG IS POSSIBLE EARLY SAT MORNING AT ALL CENTRAL NC TAF SITES. A STORM SYSTEM WILL APPROACH FROM THE WEST AND SW ON SUN... BRINGING INCREASING CHANCES FOR SUB-VFR CONDITIONS AND RAIN FOR LATE SUN THROUGH MON. -GIH && .HYDROLOGIC DISCUSSION /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...HARTFIELD NEAR TERM...BLS SHORT TERM...BLS LONG TERM...HARTFIELD AVIATION...HARTFIELD HYDROLOGY...BADGETT

USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.