Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 011432 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 1032 AM EDT WED OCT 01 2014 .SYNOPSIS...WEAK HIGH PRESSURE WILL EXTEND SOUTHWARD INTO THE REGION THROUGH THURSDAY. A COLD FRONT WILL APPROACH THE MOUNTAINS FROM THE WEST ON FRIDAY...THEN SWEEP EAST ACROSS THE CAROLINAS FRIDAY NIGHT. && .NEAR TERM /THROUGH TONIGHT/... AS OF 1030 AM WEDNESDAY... AN UPPER LEVEL LOW CENTERED ALONG THE MID-ATLANTIC COAST TODAY WILL SHIFT OFFSHORE TONIGHT AS A SHORTWAVE RIDGE BUILDS EAST TOWARD THE SOUTHERN APPALACHIANS. SMALL AMPLITUDE WAVES DIGGING SE THROUGH VA ON THE WESTERN PERIPHERY OF THE EXITING UPPER LEVEL LOW COULD PROVIDE GLANCING BOUTS OF DPVA THROUGH THIS AFT/EVE...THOUGH ONE WOULD EXPECT SYNOPTIC SUBSIDENCE TO OVERSPREAD THE REGION FROM THE WEST OVERNIGHT AS THE SHORTWAVE RIDGE PROGRESSES EAST TO THE SPINE OF THE APPALACHIANS. THE LATEST NAM CONTINUES TO DEVELOP LIGHT PRECIP OVER THE NORTHERN PIEDMONT TONIGHT...WHILE THE LATEST GFS GUIDANCE IS DRY. IT IS DIFFICULT TO ASCERTAIN WHY THE NAM CONTINUES TO DEVELOP PRECIPITATION TONIGHT...ESP WITH WEAK LOW-LEVEL FLOW... MARGINAL/SHALLOW INSTABILITY (EQUILIBRIUM LEVEL ~10 KFT)...AND INCREASING SYNOPTIC SUBSIDENCE FROM THE WEST. A MORE RIGOROUS ANALYSIS OF THE 12Z NAM IS ONGOING AND WILL BE COMPLETED BY EARLY AFTERNOON. AT THIS TIME...WILL CONTINUE TO INDICATE A DRY FCST THROUGH TONIGHT WITH HIGHS IN THE UPPER 70S TO LOWER 80S AND LOWS THU MORNING IN THE LOWER 60S. -VINCENT && .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... AS OF 250 AM WEDNESDAY... FOR THU/THU NIGHT: THE MID LEVEL CLIPPER LOW CONTINUES MOVING OFF THE NORTHEAST COAST THU/THU NIGHT... WHILE DEEP AND AMPLIFYING MID LEVEL TROUGHING SHIFTS EAST OVER THE PLAINS.... AND THIS WILL BRING A MODEST MID LEVEL RIDGE OVER NC. THE SURFACE HIGH CENTERED OVER THE CANADIAN MARITIMES WILL CONTINUE TO EXTEND WEAKLY TO THE SW/SOUTH INTO NC... ALTHOUGH ITS SOUTHERN END WILL START TO WEAKEN AND SHIFT A BIT TO THE NE IN RESPONSE TO THE ENCROACHING WARM SECTOR AND SLOWLY INCREASING LOW LEVEL WINDS FROM THE SW. EXPECT FAIR TO PARTLY CLOUDY SKIES AS LOW LEVEL MOISTURE TRANSPORT STRENGTHENS (ESPECIALLY OVER THE WESTERN HALF OF NC). THE MODELS DEVELOP PATCHES OF VERY LIGHT PRECIP OVER CENTRAL/ERN NC EARLY THU THROUGH THU AFTERNOON... WITH ADDITIONAL LIGHT PRECIP MAINLY OVER THE VA PIEDMONT THU NIGHT. WITH THE MID LEVELS STILL DRY WITH SUBSIDENCE WITHIN THE RIDGE ALOFT... ANY MOISTURE AND FORCING FOR ASCENT WOULD BE ROOTED VERY LOW. AND AT THIS TIME... WE DON`T QUITE SEE THE LIFT AND MOISTURE NECESSARY FOR ANYTHING BETTER THAN SPRINKLES. THUS... WILL LEAVE POPS UNDER 15% AND MENTION NOTHING GREATER THAN SPRINKLES. THICKNESSES INCH UP FURTHER... SUGGESTING HIGHS NEAR 80 TO 84 (COOLER READINGS NORTHEAST). LOWS MAINLY IN THE LOW 60S... AND WE SHOULD SEE AREAS OF CLOUDS AND LIGHT FOG THU NIGHT AHEAD OF THE INCOMING STORM SYSTEM. -GIH && .LONG TERM /FRIDAY THROUGH TUESDAY/... AS OF 250 AM WEDNESDAY... FRIDAY AND FRIDAY NIGHT: A DEEPENING UPPER LEVEL LOW OVER THE UPPER MID-WEST WILL MOVE EASTWARD FRIDAY AND FRIDAY NIGHT...WHILE THE TROUGH DIGS SOUTH INTO THE OH/TN RIVER VALLEY. A POTENT COLD FRONT WILL ACCOMPANY THE SURFACE TROUGH APPROACHING THE REGION FRIDAY AND FRIDAY NIGHT AS THE LOW CONTINUES ITS NORTHWARD TREK INTO CANADA. THE MODELS ARE STILL IN GOOD AGREEMENT WITH BOTH THE TIMING OF THE FRONT AND THE PRECEDING CONVECTION. THERE HAS BEEN LITTLE CHANGE IN THE MODELS SINCE THE LAST FORECAST UPDATE...THUS HAVE KEPT RAINFALL CHANCES AND AMOUNTS NEARLY THE SAME. EXPECT CHANCES TO INCREASE FROM NW TO EAST LATE FRIDAY MORNING THROUGH FRIDAY EVENING...DECREASING AGAIN THROUGH EARLY SATURDAY MORNING AS THE COLD FRONT MOVES INTO THE AREA. ALTHOUGH THERE IS DESCENT SHEAR AND LOW LEVEL LAPSE RATES...THE WEAK INSTABILITY AND MID-LEVEL LAPSE RATES...COMBINED WITH THE LATE DIURNAL TIMING...SHOULD MINIMIZE THE SEVERE THREAT. EXPECT HIGHS GENERALLY IN THE MID 70S TO LOW 80S AND LOWS MAINLY IN THE MID 50S NW TO MID 60S SE...ALTHOUGH BOTH WILL BE DEPENDENT ON THE CONVECTION AND TIMING OF THE FRONT. SATURDAY THROUGH TUESDAY: THE COLD FRONT WILL MOVE THROUGH THE REGION BY SATURDAY EVENING...WITH COOLER AND DRIER AIR MOVING IN BEHIND IT AS HIGH PRESSURE BUILDS IN. ONCE THE PRE-FRONTAL CONVECTION MOVES OUT OF THE AREA...THE REST OF THE WEEKEND SHOULD REMAIN DRY. THE UPPER LEVEL TROUGH WILL LINGER OVER THE ATLANTIC COAST...WITH POSSIBLE DISTURBANCES YIELDING A SLIGHT CHANCE FOR SOME RAIN MONDAY AND TUESDAY. ASIDE FROM THAT...THE REMAINDER OF THE FORECAST SHOULD ALSO BE MOSTLY DRY. HOWEVER...THERE IS QUITE A BIT MORE UNCERTAINTY AND DISAGREEMENT BETWEEN THE MODELS IN THIS PART OF THE FORECAST...THUS CONFIDENCE IS LOW AT THIS TIME. HIGHS SATURDAY WILL AGAIN BE DEPENDENT ON THE FRONT...BUT FOR NOW EXPECT MID 60S NW TO MID 70S SE WHILE LOWS SATURDAY NIGHT WILL BE QUITE A BIT COOLER THAN PREVIOUS NIGHTS...MID 40S NW TO LOW 50S SE. HIGHS ON SUNDAY SHOULD BE THE LOWEST OF THE EXTENDED PERIOD...MID 60S TO LOW 70S. HIGHS MONDAY AND TUESDAY WILL BE GENERALLY IN THE LOW TO MID 70S. MEANWHILE...LOWS SHOULD INCREASE FROM THE UPPER 40S TO LOW 50S SUNDAY NIGHT INTO THE LOW TO MID 50S MONDAY AND TUESDAY NIGHTS. && .AVIATION /18Z WEDNESDAY THROUGH MONDAY/... AS OF 1030 AM WEDNESDAY... 24-HR TAF PERIOD: IFR/LIFR CEILINGS ASSOCIATED WITH THE LIFTING OF WIDESPREAD DENSE FOG WILL GRADUALLY MIX OUT TO MVFR CEILINGS BY ~16Z BEFORE SCATTERING OUT ENTIRELY...WITH VFR CONDITIONS PREVAILING THIS AFTERNOON/EVENING. BASED ON PERSISTENCE...FOG/LOW CEILINGS ARE EXPECTED TO DEVELOP AGAIN LATE TONIGHT...08-12Z THURSDAY...WITH CONDITIONS IMPROVING BY LATE THU MORNING. LOOKING AHEAD: ASIDE FROM A CONTINUED POTENTIAL FOR MORNING FOG/ STRATUS ON FRIDAY...VFR CONDITIONS WILL OTHERWISE PREVAIL. WIDESPREAD ADVERSE AVIATION CONDITIONS ARE EXPECTED FRIDAY NIGHT AS A STRONG COLD FRONT CROSSES THE CAROLINAS FROM THE WEST... ACCOMPANIED BY WIDESPREAD SHOWERS AND ISOLATED THUNDERSTORMS. VFR CONDITIONS WILL PREVAIL IN THE WAKE OF THE FRONT THIS WEEKEND AS HIGH PRESSURE BUILDS INTO THE REGION FROM THE WEST. -VINCENT && $$ SYNOPSIS...VINCENT NEAR TERM...VINCENT SHORT TERM...HARTFIELD LONG TERM...KC AVIATION...VINCENT

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