Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 230835 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 435 AM EDT TUE SEP 23 2014 .SYNOPSIS...A STALLED UPPER LEVEL LOW AND ATTENDANT COASTAL LOW PRESSURE SYSTEM WILL LINGER OVER THE CAROLINAS THROUGH WEDNESDAY... THEN TRACK OFFSHORE THE MID-ATLANTIC COAST WEDNESDAY NIGHT. HIGH PRESSURE WILL EXTEND SOUTHWARD INTO THE REGION ON THURSDAY AND FRIDAY. && .NEAR TERM /TODAY AND TONIGHT/... AS OF 200 AM TUESDAY... OVERVIEW: A POTENT UPPER LEVEL LOW CENTERED OVER EAST-CENTRAL GA AT 06Z WILL TRACK INTO SC THIS MORNING...THEN STALL OUT OVER THE CAROLINAS THROUGH TONIGHT. SHORTWAVE ENERGY ROTATING AROUND THE UPPER LOW WILL AID IN CYCLOGENESIS IN VICINITY OF A COASTAL FRONT SITUATED ALONG OR JUST OFFSHORE THE SOUTHEAST COAST TONIGHT AS HIGH PRESSURE OVER THE MID-ATLANTIC EXTENDS SOUTHWARD THROUGH CENTRAL AND WESTERN PORTIONS OF THE CAROLINAS. PRECIPITATION: FORECAST UNCERTAINTY PERSISTS W/REGARD TO THE PRECISE EVOLUTION OF THE CUT-OFF LOW OVER THE REGION...ESPECIALLY W/REGARD TO THE TIMING/STRENGTH/LOCATION OF SHORTWAVE ENERGY ROTATING AROUND THE LOW AND THE INFLUENCE OF CONVECTIVE PRECIPITATION EXPECTED TO DEVELOP IN VICINITY OF THE COASTAL FRONT ALONG THE SOUTHEAST COAST TODAY/TONIGHT. THE LATEST 00Z GFS/NAM GUIDANCE INDICATE A POTENTIAL FOR ELEVATED CONVECTION UNDER THE COLD POOL ALOFT IN CENTRAL/WESTERN NC TODAY...IN ADDITION TO A POTENTIAL FOR ELEVATED CONVECTION ON THE COOL SIDE OF THE COASTAL FRONT IN THE SE COASTAL PLAIN...WITH THE BEST CHANCE LATE TONIGHT IN THE COASTAL PLAIN AS THE COASTAL FRONT SHARPENS AND EDGES CLOSER TO THE COAST IN ADVANCE OF A DEVELOPING WAVE OF LOW PRESSURE. UNTIL ADDITIONAL GUIDANCE AND OBSERVATIONAL DATA CAN BE ASSESSED...WILL INDICATE PRECIPITATION CHANCES AS MENTIONED ABOVE. TEMPS: CHALLENGING TEMPERATURE FORECAST. BROKEN TO OVERCAST MID- LEVEL CEILINGS OVER THE BULK OF CENTRAL NC WILL INHIBIT INSOLATION AND KEEP TEMPS COOLER THAN YESTERDAY...THOUGH EXACTLY HOW COOL WILL HIGHLY DEPEND ON THE TIMING/LOCATION OF PRECIPITATION THAT DEVELOPS. IF THE GFS SOLUTION VERIFIES...I.E. ELEVATED PRECIPITATION INLAND OVER THE WESTERN PIEDMONT...TEMPS WOULD HAVE DIFFICULTY EXCEEDING THE 50S TODAY. HOWEVER...IF THE NAM SOLUTION VERIFIES...I.E. NO INLAND PRECIPITATION...TEMPS IN THE TRIAD WOULD RISE INTO THE UPPER 60S. AT THIS TIME WILL INDICATE HIGHS IN THE 60S OVER ALL OF CENTRAL NC. EXPECT RELATIVELY LITTLE DIURNAL VARIATION IN TEMPS WITH LOWS TONIGHT IN THE 50S TO LOWER 60S. -VINCENT && .SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/... AS OF 253 AM TUESDAY... FORECAST UNCERTAINTY REMAINS ABOVE AVERAGE AS MODEL GUIDANCE CONTINUES TO HAVE DIFFICULTY IN CAPTURING THE PRECISE EVOLUTION OF A STALLED UPPER LEVEL LOW OVER THE SOUTHEAST CONUS...AND WITH PRECIPITATION ALONG THE SOUTHEAST COAST. THE LATEST GUIDANCE IS SIMILAR IN NATURE TO PREVIOUS GUIDANCE...SHOWING THE BEST POTENTIAL FOR RAIN ALONG/EAST OF HWY 1 DURING THE DAY WEDNESDAY AS A WAVE OF LOW PRESSURE ATTENDANT SHORTWAVE ENERGY ROTATING AROUND THE DEAMPLIFYING UPPER LEVEL LOW TRACKS NORTHWARD ALONG A RETROGRADING COASTAL FRONT. THE PRECISE TIMING/LOCATION OF SHORTWAVE ENERGY ROTATING AROUND THE UPPER LOW AND ULTIMATELY THE PRECISE TIMING/TRACK OF THE ATTENDANT WAVE OF LOW PRESSURE ALONG THE RETROGRADING (WESTWARD/INLAND MOVING) COASTAL FRONT IS DIFFICULT TO ASSESS...EVEN AT SHORT RANGE. QUALITATIVELY...EXPECT BROKEN TO OVERCAST CLOUD COVER EVERYWHERE AND AN INCREASING CHANCE OF RAIN FROM THE TRIANGLE EASTWARD TO THE COAST WITH TEMPS STRUGGLING TO EXCEED THE 60S. PRECIPITATION CHANCES SHOULD DECREASE FROM SW-NE WED NIGHT AS THE LINGERING UPPER LEVEL LOW BECOMES PROGRESSIVE IN RESPONSE TO STRENGTHENING SOUTHWESTERLY FLOW ALOFT IN ADVANCE OF SHORTWAVE ENERGY TRACKING EASTWARD FROM THE CENTRAL PLAINS INTO THE WESTERN OH VALLEY...THOUGH THIS FEATURE ITSELF IS EMBEDDED IN WEAK STEERING FLOW AND EXPECTED TO CUT-OFF OVER THE CENTRAL MS RIVER VALLEY WED NIGHT/THU...INTRODUCING MORE UNCERTAINTY THAN WOULD OTHERWISE BE THE CASE. ONCE AGAIN...EXPECT LITTLE DIURNAL VARIATION IN TEMPS WITH LOWS IN THE 50S/60S. WIND: THE MSLP/HEIGHT GRADIENT WILL TIGHTEN OVER CENTRAL NC WEDNESDAY...BETWEEN STRONG HIGH PRESSURE TO THE NORTH AND A DEVELOPING LOW PRESSURE SYSTEM ALONG THE CAROLINA COAST...AND FCST SOUNDINGS SUGGEST LOW-LEVEL NORTHEAST FLOW AS STRONG AS 30-40 KT. SHALLOW MIXING ASSOCIATED WITH LOW-LEVEL COLD ADVECTION WILL BE ENHANCED BY PRECIPITATION /EVAP COOLING/ ON WED...ESP IN THE SE COASTAL PLAIN WHERE A TIGHTER MSLP GRADIENT WILL BE JUXTAPOSED WITH HEAVIER PRECIPITATION. WITH THE ABOVE IN MIND...AREAS SOUTH AND EAST OF THE TRIANGLE COULD SEE A PERIOD OF BREEZY NORTHEAST WINDS GUSTING AS HIGH AS 30-40 MPH DURING THE DAY WED. KEEP IN MIND THAT THIS WOULD BE A WORST-CASE SCENARIO AND THAT WIND OF THIS MAGNITUDE WOULD FALL SHORT OF WIND ADVISORY CRITERIA...THOUGH PERHAPS CAPABLE OF A FEW DOWNED TREES IN THE PRESENCE OF HEAVY PRECIPITATION. -VINCENT && .LONG TERM /THURSDAY THROUGH MONDAY/... AS OF 330 AM TUESDAY... SOME DRYING MAY BEGIN SOONER THAN PREVIOUSLY EXPECTED AS THE MID/UPPER LOW AND ASSOCIATED SURFACE TROUGH SHOULD BE QUICKER TO EXIT. AT LEAST SOME RESIDUAL CLOUDINESS IS EXPECTED THURSDAY AS THE SURFACE WAVE MOVES SLOWLY UP THE MID- ATLANTIC COAST... WITH CLEARING IN THE LEE OF THE MOUNTAINS SPREADING SE DURING THE DAY. THE NEXT CHANCE OF RAIN SHOULD COME EARLY NEXT WEEK. HOWEVER... MODELS CONTINUE TO SHOW PLENTY OF DISAGREEMENT. ALL IN ALL... TEMPERATURES SHOULD TURN MILDER LATE WEEK AS THE CLOUDS DEPART. HOWEVER... THE PROLONGED NE FLOW COURTESY OF HIGH PRESSURE TO OUR NE WILL KEEP READINGS IN CHECK. && .AVIATION /06Z TUESDAY THROUGH SATURDAY/... AS OF 200 AM TUESDAY... 24-HR TAF PERIOD: EXPECT VFR CONDITIONS TO PREVAIL THROUGH THE TAF PERIOD WITH CEILINGS GENERALLY NO LOWER THAN 5-8 KFT AND A NORTHEAST BREEZE AT 5-10 KT...EXCEPT 10-15 KT AT THE FAY TERMINAL LATER TODAY INTO TONIGHT AS THE MSLP GRADIENT TIGHTENS ALONG THE SOUTHEAST COAST. ANY CHANCE FOR SUB-VFR CONDITIONS SHOULD BE CONFINED TO THE FAY/RWI TERMINALS AT THE END OF THE TAF PERIOD WHEN PRECIPITATION AND MVFR CEILINGS MAY SPREAD INLAND IN ADVANCE OF A WAVE OF LOW PRESSURE TRACKING NE ALONG THE FRONTAL ZONE STALLED IN VICINITY OF THE SE COAST. LOOKING AHEAD: SUB-VFR CONDITIONS ASSOC/W RAIN WILL BE POSSIBLE AT THE RDU/FAY/RWI TERMINALS ON WEDNESDAY AS THE AFOREMENTIONED WAVE OF LOW PRESSURE TRACKS NORTHWARD ALONG THE MID-ATLANTIC COAST...THOUGH UNCERTAINTY PERSISTS WITH REGARD TO HOW FAR WEST PRECIPITATION WILL DEVELOP AND THE RELATIVE BEST CHANCE FOR SUB-VFR CONDITIONS WILL BE AT THE FAY/RWI TERMINALS. OTHERWISE...EXPECT VFR CONDITIONS TO PREVAIL THROUGH THE REMAINDER OF THE WEEK AS HIGH PRESSURE EXTENDS INTO THE CAROLINAS FROM THE NORTH. -VINCENT && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...VINCENT NEAR TERM...VINCENT SHORT TERM...VINCENT LONG TERM...PWB AVIATION...VINCENT

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