000 FXUS62 KRAH 071401 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 1000 AM EDT SUN SEP 7 2008 .SYNOPSIS...A WEAK SURFACE TROUGH WILL LINGER OVER THE SANDHILLS AND COASTAL PLAIN TODAY...POSSIBLY TRIGGERING ISOLATED THUNDERSTORMS THIS AFTERNOON. WEAK HIGH PRESSURE WILL RESIDE OVER THE AREA MONDAY. .NEAR TERM /THROUGH TONIGHT/... AS OF 10 AM EDT SUNDAY... WEAK SURFACE HIGH PRESSURE IS EDGING INTO CENTRAL NORTH CAROLINA TODAY. THIS WEAK LOW LEVEL FLOW IS SLOWLY ADVECTING DRIER AIR IN FROM THE NORTH AND NORTHWEST. WE HAVE MUCH DRIER AIR ALOFT WITH A STRONG CAP OVER THE CWFA. THIS CAP IS WEAKER IN THE SOUTHEAST IN THE VICINITY OF A SURFACE TROF AND MOST ABUNDANT LOW LEVEL MOISURE...BUT THE CAP WILL BE STRENGTHENING TODAY. AS SUCH...A SLIGHT CHANCE OF AFTERNOON CONVECTION LOOKS POSSIBLE IN THE SOUTHERN COASTAL PLAIN. THE THIN LAYER OF MID LEVEL MOISTURE WILL BE MIXING OUT AND ONLY A SCATTERED CU FIELD AS WE APPROACH MAX HEATING WILL ALLOW FOR MOSTLY SUNNY. HIGHS ON TRACK TO REACH 88-92 ACROSS THE AREA. TONIGHT...EXPECT MOSTLY CLEAR TO PARTLY CLOUDY SKIES. RESIDUAL GROUND MOISTURE FROM RECENT HEAVY RAIN MAY LEAD TO FORMATION OF FOG WHICH MAY BE DENSE IN SPOTS. MIN TEMPS MAINLY IN THE 65-70 DEGREE RANGE. .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... AS OF 330AM SUNDAY... ON MONDAY...850-700MB RIDGE AXIS ACROSS FORECAST AREA MONDAY MORNING SHIFTS EAST MONDAY AFTERNOON EVENING. AS RIDGE MOVES EAST IN THE AFTERNOON...RETURN FLOW COMMENCES WITH SOME WEAK CONFLUENCE NOTED IN THE FAR SOUTH WHICH COINCIDES WITH A SHEAR AXIS ALOFT THAT MIGRATES NORTH FROM SC. AIR MASS EXPECTED TO BE MODERATELY UNSTABLE WITH LIFTED INDICES AROUND MINUS 4 AND PRECIP WATER VALUES AROUND 1.5-1.7 INCHES. THIS TYPE OF AIRMASS SHOULD SUPPORT ISOLATED CONVECTION ANYWHERE IN THE FORECAST AREA BUT EXPECT BETTER CHANCE FOR ISOLATED CONVECTION OVER THE SOUTHERN AND WESTERN COUNTIES. THICKNESSES REMAIN ABOUT 10M WARMER THAN NORMAL...SUPPORTING MAX TEMPS ONCE AGAIN WELL INTO THE 80S TO AROUND 90. MOIST AND MARGINALLY UNSTABLE AIR MASS WILL LINGER OVER REGION TUE. APPROACH OF A BETTER DEFINED S/W CROSSING THE LOWER OH VALLEY WILL ENHANCE LOW LEVEL SOUTHERLY FLOW OVER OUR REGION. APPROACH OF THIS MID LEVEL FEATURE WILL LIKELY INCREASE THREAT FOR CONVECTION...ESPECIALLY LATE IN THE DAY OVER THE NW AND OVERNIGHT TUESDAY NIGHT OVER MOST OF THE REGION. BETTER UPPER DIVERGENCE OCCURS AFTER 00Z WED ACROSS THE NORTH WHILE 850MB CONFLUENCE INCREASES TUESDAY NIGHT INTO WED WITH APPROACH OF 850MB TROUGH. THIS SUPPORTS PREVIOUS FORECAST OF PRECIP CHANCES TUESDAY NIGHT. INCREASE IN CLOUDINESS AND A BIT MORE CONVECTIVE COVERAGE SUGGEST MAX TEMPS TUESDAY SHOULD BE A FEW DEGREES COOLER. MAX TEMPS MID/UPPER 80S. MIN TEMPS TUESDAY NIGHT IN THE 60S TO AROUND 70. .LONG TERM /WEDNESDAY THROUGH SATURDAY/... AS 330 AM SUNDAY... BOTH THE GFS AND EC HAVE ACTUALLY SHOWN GOOD RUN-TO-RUN CONTINUITY IN REGARDS TO A BACK-DOOR COLD FRONTAL PASSAGE ON WEDNESDAY...WHICH THEN QUICKLY ATTEMPTS TO MORPH INTO A SHORT-LIVED HYBRID CAD WEDNESDAY NIGHT/THURSDAY AS A WEAK PARENT HIGH 1030 MBCENTERED OVER NY/PA EXTENDS SOUTH DOWN THE EASTERN SLOPES OF THE APPALACHIANS. FRONT STALLS OUT ALONG THE COAST AS THE EXPANSIVE SUBTROPICAL RIDGE EXTENDS OVER THE SOUTHEAST CONUS. AS IKE TRACKS WEST ACROSS CUBA...SOUTH OF THE THE EXPANSIVE RIDGE...A TROPICAL PLUME OF MOISTURE SURGES NORTH TOWARDS THE CAROLINA COAST WEDNESDAY NIGHT AND INTO THURSDAY. MODELS INDICATE OVERRUNNING PRECIP BREAKS OUT ACROSS CENTRAL NC...IN THE COOL/STABLE STABLE SECTOR ON THURSDAY AS LOW-LEVEL SELY ONSHORE FLOW EXPANDS NORTHWEST OVER THE AREA. THE GFS IS MORE ROBUST WITH PRECIP AND LIFT AS THE GFS INDICATES BETTER UPPER LEVEL SUPPORT WITH ENTRANCE REGION OF UPPER JET HUGGING THE COAST. THE LATEST GFS AND EC SUGGEST HIGH TEMPERATURES ON THURSDAY...SOME 15 TO 20 DEGREES BELOW NORMAL...WITH NORTHERN/NW AREAS REMAINING IN THE 60S. WITH THE UPPER RIDGE STILL OVER THE SOUTHEAST...OVERALL LIFT SHOULD BE WEAK...SUGGESTING QPF/PRECIP WILL BE VERY LIGHT OR POSSIBLY EVEN DRIZZLE. IT SHOULD BE NOTED THAT CENTRAL NC IS ENTERING IN ONE OF TWO CLIMATOLOGICALLY FAVORED TIMES OF YEAR FOR CAD EVENTS...SO IT APPEARS MOTHER NATURE IS RIGHT ON CUE. LOWERED THURSDAYS HIGH ONE CATEGORY...BUT FURTHER MORE SIGNIFICANT CHANGES WILL BE NEEDED IF CURRENT DEPICTION HOLDS TRUE. INSTABILITY RETURNS ON FRIDAY AS THE DAMMING HIGH MOVES EAST AND OFFSHORE...WITH THE ENCROACHMENT OF A COLD FRONT ON SATURDAY. .AVIATION /07Z SUNDAY THROUGH THURSDAY/... AS OF 730 AM SUNDAY... PATCHY FOG WILL CLEAR AFTER 13-14Z...WITH VFR CONDITIONS AND LIGHT AND VARIABLE WINDS. HIGH PRESSURE WILL TAKE CONTROL OF THE AREA WEATHER LATE SUNDAY INTO MONDAY. DENSE FOG WILL POSE RISK AGAIN TONIGHT...WITH CALM WINDS AND CLEAR SKIES...ESPECIALLY IN THE EAST WHERE HIGHER DEWPOINTS AREA EXPECTED TO RESIDE. A BACK-DOOR COLD FRONT WILL APPROACH THE AREA LATE TUESDAY/EARLY WEDNESDAY...MOVING SOUTH OF THE AREA BY WEDNESDAY EVENING. THE FRONTAL PASSAGE WILL LEAD TO A CHANCE FOR SCATTERED RAIN SHOWERS WITH MVFR TO IFR CEILINGS. .RAH WATCHES/WARNINGS/ADVISORIES... NONE. SYNOPSIS...WSS NEAR TERM...MLM SHORT TERM...WSS LONG TERM...CBL AVIATION...CBL