Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 191133 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 633 AM EST WED NOV 19 2014 .SYNOPSIS...CHILLY HIGH PRESSURE WILL HOLD OVER THE SOUTHEAST STATES TODAY AND TONIGHT. A DRY COLD FRONT WILL DROP INTO THE REGION LATE THURSDAY. ANOTHER HIGH PRESSURE AREA WILL THEN BUILD IN FROM THE NORTH FRIDAY THROUGH SATURDAY. A STORM SYSTEM WILL BRING GOOD RAIN CHANCES TO THE REGION ON SUNDAY. && .NEAR TERM /THROUGH TONIGHT/... AS OF 220 AM WEDNESDAY... STILL FORECASTING RECORD LOW TEMPERATURES TONIGHT AND FOR GOOD REASON AS GREAT RADIATIONAL COOLING CONDITIONS HAVE LED TO KRDU ALREADY TYING THE RECORD LOW OF 21 DEGREES SET OVER 110 YEARS AGO IN 1903 WITH PLENTY OF TIME LEFT FOR IT TO FALL FURTHER. KGSO AND KFAY COULD ALSO ACHIEVE RECORD LOWS BY SUNRISE. UNCLEAR AT THIS TIME WHETHER OR NOT KFAY CURRENT TEMP OF 28 DEGREES IS REPRESENTATIVE OR NOT AS ALL SITES AROUND THEM ARE AT LEAST 6 DEGREES COLDER AT THIS HOUR. WIND HAS NOT YET GONE CALM YET AT KFAY WHICH COULD BE THE REASON FOR THE DELAYED TEMPERATURE FALL. RURAL AREAS HAVE FALLEN INTO THE UPPER TEENS AND WILL PROBABLY REACH AT LEAST MIDDLE TEENS. THE HIGH PRESSURE RESPONSIBLE FOR THE GREAT RADIATIONAL COOLING WILL CONTINUE TO REMAIN OVERHEAD THROUGH THE DAY KEEPING THINGS DRY AND MOSTLY CLEAR. ONE CAVEAT TO THAT WILL BE THE PASSING OF AN UPPER LEVEL VORT MAX WHICH WILL HELP SOME MID TO HIGH LEVEL CLOUDS STREAM IN ACROSS THE NORTH. AS THE SURFACE HIGH MOVES EAST...NORTHWESTERLY WINDS WILL GRADUALLY BECOME SOUTHWESTERLY WITH SOME GUSTING POSSIBLE TO 15 KTS DURING THE AFTERNOON IN THE NORTHWEST PIEDMONT WHICH WILL BE WHERE THE TIGHTEST PRESSURE GRADIENT IN THE CWA WILL BE. ALL OTHER AREAS SHOULD REMAIN 5-10 KTS SUSTAINED. SOME SLIGHT MODERATION IN THICKNESS VALUES WILL BRING MAX TEMPS BACK UP INTO THE LOW TO MID 40S FOR HIGHS THIS AFTERNOON. LOW TEMPERATURES THURSDAY MORNING WILL BE BACK ABOVE RECORD TERRITORY BUT STILL WELL BELOW NORMAL. MID TO UPPER 20S EXPECTED. && .SHORT TERM /THURSDAY AND THURSDAY NIGHT/... AS OF 220 AM WEDNESDAY... CONTINUED RELAXATION OF THE UPPER TROUGH AND MODERATION OF THICKNESS VALUES BACK UP TO 1315 OR SO BY THURSDAY AFTERNOON WILL PUT HIGH TEMPS BACK INTO THE LOW TO MID 50S FOR THURSDAY. THIS WILL BE HALTED SLIGHTLY BY A WEAK DRY COLD FRONT ASSOCIATED WITH LOW PRESSURE OVER QUEBEC WHICH WILL BRING A REINFORCING SHOT OF COLD AIR TO THE CWA AND KEEP LOWS THURSDAY NIGHT IN THE UPPER 20S TO LOW 30S. SCATTERED TO BROKEN CLOUDS JUST BELOW 5 KFT COULD HINDER INSOLATION SOMEWHAT AND KEEP MAX TEMPS FROM REACHING THEIR FULL SUN POTENTIAL. OTHERWISE A MOSTLY SUNNY AND BREEZY DAY EXPECTED WITH SOUTHWESTERLY WIND GUSTS OF 15-20 MPH POSSIBLE. && .LONG TERM /FRIDAY THROUGH TUESDAY/... AS OF 210 AM WEDNESDAY... FOR FRI/FRI NIGHT: THE DIFFUSE SURFACE FRONT IS EXPECTED TO DROP SOUTHWARD INTO NC BY FRI MORNING... AS SURFACE HIGH PRESSURE CENTERED OVER THE OH VALLEY STARTS BUILDING SE INTO THE AREA. LIGHT NE LOW LEVEL FLOW AND WEAK COOL AIR ADVECTION WILL CURB WARMING FRI DESPITE FAIR SKIES. WE SHOULD SEE SOME HIGH CLOUDS ESPECIALLY EARLY IN THE DAY AS A STREAK OF WEAK VORTICITY SHEARS INTO THE AREA FROM THE WEST. FRI THICKNESSES WILL STILL BE 25-30 M BELOW SEASONAL NORMALS... AND USING 925 MB TEMPS TO ACCOUNT FOR THE SHALLOW MIXED LAYER YIELDS HIGHS IN THE MID 40S NORTH TO MID 50S SOUTH... THE GREATER-THE-USUAL DIFFERENTIAL THE RESULT OF THE DIFFUSE FRONTAL ZONE. THESE COOL HIGH TEMPS ARE SUPPORTED BY BIAS-CORRECTED STATISTICAL GUIDANCE AS WELL. THE CENTER OF THE SURFACE HIGH DRIFTS EASTWARD TO THE MIDATLANTIC SHORE FRI NIGHT... WHILE NOSING SOUTHWARD INTO CENTRAL NC. LIGHT WINDS AND LITTLE TO NO CLOUD COVER FRI NIGHT WILL FACILITATE GOOD RADIATIONAL COOLING... AND LATEST GUIDANCE HAS LIKEWISE TRENDED COOLER... SO HAVE BROUGHT LOWS DOWN FRI NIGHT A COUPLE OF DEGREES TO 25-30. FOR SAT/SAT NIGHT: THE SURFACE HIGH WILL CONTINUE SHIFTING EASTWARD OUT OVER THE ATLANTIC DURING THIS PERIOD... WITH A PORTION OF THE HIGH EXTENDING BACK OVER NC. WEAK INVERTED TROUGHING STARTS TO FORM OVER THE SOUTHEAST COAST... ASSOCIATED WITH THE NORTHWARD-TRACKING WARM FRONT. THE GFS/ECMWF BOTH HOLD THIS FRONT JUST SOUTH OF NC THROUGH 12Z SUN... WITH THE COOLER AIR MASS HOLDING OVER THE FORECAST AREA. BOTH MODELS ALSO DEPICT INCREASING OVERRUNNING FLOW TO OUR SOUTHWEST... AHEAD OF A SHORTWAVE TROUGH EXPECTED CROSS TX SAT THEN PIVOT ENE ACROSS THE LOWER MISS VALLEY SAT NIGHT. THE APPROACH OF THIS WAVE WILL ACTUALLY SERVE TO TEMPORARILY BUILD UP LOW AND MID LEVEL RIDGING OVER THE MIDATLANTIC REGION... LIKELY DELAYING THE ARRIVAL OF THE ONSET OF RAIN FROM THE SW UNTIL AFTER SAT NIGHT... ALTHOUGH THE ECMWF IS A BIT FASTER THAN THE GFS HOWEVER... AND IT DOES BRING SHOWERS INTO THE WRN/SW CWA PRIOR TO SUNRISE SUNDAY. THE GFS/ECMWF STRONGLY INDICATE A GOOD POTENTIAL FOR ORGANIZED CONVECTION FROM ERN TX ACROSS THE CENTRAL/SRN GULF STATES SAT/SAT NIGHT... NEAR THE NORTHWARD-MOVING WARM FRONT AND WITHIN THE WARM SECTOR... AND THIS WILL BE WHERE THE GREATEST ACTION IS FOCUSED... AND MAY BRIEFLY ENHANCE SUBSIDENCE DOWNSTREAM OVER NC. WILL TRIM BACK AND DELAY POPS... BRINGING IN LOW CHANCES IN THE SW LATE SAT NIGHT. THICKNESSES CONTINUE TO CLIMB... ALTHOUGH THIS WON`T BE FULLY REALIZED WITH MOST WARMING TAKING PLACE ABOVE THE SHALLOW MIXED LAYER. HIGHS FROM 52-60... HIGHEST SE. EXPECT INCREASING CLOUDS SAT NIGHT AS LOW STRATUS STARTS TO OVERSPREADS THE AREA LATE WITH STRENGTHENING 850 MB SSE FLOW TO 30-40 KTS. LOWS 38-45. FOR SUN/SUN NIGHT: GREATEST FORECAST UNCERTAINTY REMAINS ON THIS DAY. WIDESPREAD RAIN AND SHOWERS ARE LOOKING LIKE A SLAM-DUNK... AS THE INITIAL MISS-VALLEY SHORTWAVE DAMPENS AND DRAWS NORTHWARD TOWARD THE GREAT LAKES... TAKING ITS ENERGY MAINLY WEST OF NC... WHILE STRONGER VORTICITY CENTERS DIG INTO THE MAIN TROUGH OVER THE SOUTH- CENTRAL STATES... NUDGING THE STRONGER SW CYCLONIC STEERING FLOW EASTWARD TOWARD NC. WILL GO WITH CATEGORICAL POPS EVERYWHERE... SPREADING SW TO NE... FUELED BY 40-50 KT 850 MB FLOW FROM THE SSE AND A SURGE OF 1.5"+ PRECIP WATER... WITH LARGE SCALE LIFT ENHANCED BY INTENSE UPPER DIVERGENCE ASSOCIATED WITH A 120 KT SRLY UPPER JET OVER THE OH VALLEY. COVERAGE AND QPF ARE LIKELY TO BE GREATEST ACROSS NW NC... NEAR THE BEST DYNAMICS... WHILE CONVECTION OVER SRN GA AND SRN/ERN SC COULD LIMIT QPF SOMEWHAT ACROSS OUR SRN AND ERN COUNTIES. BOTH THE GFS AND ECMWF TAKE THE WARM FRONT NORTHWARD THROUGH NC SUNDAY... HOWEVER BOTH ARE NOW HOLDING A POCKET OF THE COOLER/MORE STABLE AIR ALONG THE EAST SLOPES... THROUGH THE NC FOOTHILLS AND FAR NW PIEDMONT. EXACTLY HOW FAR NW THIS WARM FRONT WILL GET IS THE $64,000 QUESTION. MODELS CONTINUE TO IMPROVE THEIR ABILITY TO PICK UP ON RESIDUAL COOL POOLS LOCKED IN BY OVERRUNNING FLOW AND PHYSICALLY BLOCKED BY THE TERRAIN... BUT THE DETAILS REMAIN MURKY. WILL STICK WITH THE EARLIER TRENDS OF HOLDING WELL BELOW STATISTICAL GUIDANCE IN THE NW CWA WHILE ALLOWING WARM MOIST AIR TO OVERSPREAD THE REMAINDER OF THE FORECAST AREA. HIGHS IN THE 60S TO NEAR 70... EXCEPT FOR LOW-MID 50S IN THE FAR NW. THE BEST FORCING FOR ASCENT AND MOISTURE TRANSPORT BOTH SHIFT TO OUR NE BY SUN EVENING IN CONJUNCTION WITH A SHIFT OF STRONG 850 MB WINDS TO SWRLY AND WITH THE ARRIVAL OF THE MID LEVEL DRY PUNCH... SO EXPECT PRECIP TO WIND DOWN RAPIDLY TO MORE PATCHY OR SCATTERED SHOWERS FROM MID EVENING THROUGH SUN NIGHT. IT SHOULD BE QUITE WARM... AND EXPECT WHAT IS LEFT OF THE RESIDUAL COOL POOL IN THE FAR NW CWA TO BE OVERWHELMED BY THE STRONG WARM AIR ADVECTION... CAUSING TOP-DOWN WEDGE EROSION. LOWS FROM THE LOW 50S NW (WHERE TEMPS SHOULD HOLD STEADY FROM SUNDAY TEMPS OR RISE A BIT OVERNIGHT) WITH UPPER 50S TO MID 60S ELSEWHERE. FOR MON/TUE: SHORTWAVE ENERGY RIDES UP ON THE SE SIDE OF THE MEAN TROUGH UP ALONG THE APPALACHIANS MON... AS A WEAKENING AND DIFFUSE COLD FRONT PUSHES SLOWLY EASTWARD INTO WRN NC. THE ECMWF IS A BIT FASTER THAN THE GFS... BRINGING A BAND OF MORE NUMEROUS FRONTAL SHOWERS MON... WHEREAS THE GFS IS LESS ROBUST AND HOLDS IT OFF UNTIL MON EVENING. CONSIDERING THE NET FRONTOLYSIS TAKING PLACE AS THE MID LEVEL FLOW BECOMES NEARLY PARALLEL TO THE SURFACE FRONTAL ZONE... A LATER FRONTAL APPROACH APPEAR MOST REASONABLE. EXPECT WARM HIGHS MON (ABOVE NORMAL FOR A CHANGE!) FROM THE UPPER 60S TO MID 70S... WITH SCATTERED SHOWERS. A MODEST COOLDOWN IS EXPECTED TUE AS THIS INITIAL FRONT HEADS TO OUR EAST... BUT WITH THE SECONDARY STRONGER COLD FRONT STILL TO OUR WEST THROUGH TUE... MOVING JUST TO THE OH VALLEY... WILL KEEP TEMPS CLOSE TO SEASONAL NORMALS. ONLY A SMALL RAIN CHANCE IN THE EAST TUE IN THE ABSENCE OF DECENT MOISTURE OR ANY SIGNIFICANT LIFT. -GIH && .AVIATION /12Z WEDNESDAY THROUGH SUNDAY/... AS OF 630 AM WEDNESDAY... 24 HOUR TAF PERIOD: HIGH CONFIDENCE OF VFR CONDITIONS THROUGH THE TAF PERIOD. CALM WINDS AND CLEAR SKIES TO START THE DAY WILL EVENTUALLY GIVE WAY TO SOUTHWESTERLY WINDS AT 5-10 KTS POSSIBLY GUSTING TO 15 KTS IN THE NORTHWEST PIEDMONT. SOME MID TO HIGH LEVEL CLOUDS ARE POSSIBLE ACROSS THE NORTH LATER THIS AFTERNOON WITH LESS COVERAGE IN THE SOUTH. NO PRECIPITATION IS EXPECTED. LONG TERM: THE NEXT THREAT TO AVIATION CONDITIONS WILL BE WITH A SYSTEM ON SUNDAY INTO MONDAY. && .CLIMATE... THE FOLLOWING ARE RECORD TEMPERATURES THAT WILL BE CHALLENGED THROUGH THE FORECAST PERIOD: RECORD LOW: GSO RDU FAY WED 11/19 - 20 IN 1951 21 IN 1903 21 IN 1959 THU 11/20 - 12 IN 1951 19 IN 1951 20 IN 1951 RECORD LOW MAX: GSO RDU FAY WED 11/19 - 34 IN 1951 36 IN 1951 41 IN 2000 && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...HARTFIELD NEAR TERM...ELLIS SHORT TERM...ELLIS LONG TERM...HARTFIELD AVIATION...ELLIS CLIMATE...MWS

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