Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 210723 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 320 AM EDT THU AUG 21 2014 .SYNOPSIS...A SERIES OF UPPER LEVEL DISTURBANCES IN NORTHWEST FLOW ALOFT WILL CROSS THE REGION THROUGH LATE WEEK. A BACK DOOR COLD FRONT IS FORECAST TO SLIP INTO THE AREA OVER THE WEEKEND. && .NEAR TERM /THROUGH TONIGHT/...
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AS OF 320 AM WEDNESDAY... UPPER RIDGE OVER THE CNTRL U.S. WILL UNDERGO GRADUAL AMPLIFICATION ...WHILE THE GREAT LAKES UPPER UPPER LOW WILL WEAKEN INTO AN OPEN WAVE TROUGH AS IT MOVES OVER THE NORTHEAST US. IN RESPONSE...HEIGHTS ALOFT INCREASE OVER THE CAROLINAS WITH ASSOCIATED WARMING ALLOWING H8 TEMPS TO RISE TO AROUND 21C...A 3C DEGREE INCREASE FROM WEDNESDAY. COUPLED WITH COMPRESSIONAL/DOWNSLOPE WARMING EAST OF THE MTNS AND SEASONABLY DEEP ADIABATIC MIXING...HIGHS THIS AFTERNOON SHOULD BE WELL INTO THE 93 TO 98 DEGREE RANGE. THIS DEEP MIXING SHOULD ALSO HELP SFC DEWPOINTS TO MIX OUT INTO THE 60S THIS AFTERNOON...WHICH SHOULD KEEP HEAT INDICES IN THE 100-103F RANGE FROM THE CENTRAL PIEDMONT EASTWARD. WHILE THIS IS BELOW ADVISORY CRITERIA...RECENT EXTENDED PERIOD OF BELOW NORMAL TEMPERATURES DURING THE FIRST 2-3 WEEKS OF AUGUST MAY MAKE THE GENERAL POPULACE A LITTLE MORE SENSITIVE TO THE ABOVE HEAT INDICES...AND THUS WILL ADD A HEADLINE IN THE HWO. WILL HAVE TO MONITOR UPSTREAM TRENDS...BUT THERE APPEARS TO BE A VOID OF ANY APPRECIABLE FORCING VIA SHORTWAVE DISTURBANCES IN THE NW FLOW ALOFT. WILL RETAIN ISOLATED TO SLIGHT CHANCE POPS WITH FORCING LIMITED TO THE RESIDUAL/THERMAL TROUGH IN PLACE. OVERNIGHT LOWS IN THE LOWER 70S.
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&& .SHORT TERM /FRIDAY AND FRIDAY NIGHT/...
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AS OF 320 AM THURSDAY... UPPER RIDGE OVER THE CENTRAL US CONTINUES TO AMPLIFY AS THE UPPER TROUGH MOVES OFF THE MID-ATLANTIC COAST. WHILE THERE CONTINUES TO BE CONSIDERABLE RUN-TO-RUN VARIABILITY WITH HOW NWP GUIDANCE HANDLE INDIVIDUAL SHORTWAVES EMBEDDED IN THE MEAN TROUGH...THE OVERRIDING THEME OVER THE LAST SEVERAL DAYS HAS BEEN RATHER CONSISTENT IN SHOWING AN INCREASE/UPTICK IN RAIN CHANCES/POPS LATE FRIDAY AND INTO FRIDAY NIGHT IN RESPONSE TO THE BROADER SYNOPTIC SCALE ASCENT MOVING DOWN THE MID-ATLANTIC COAST AND ATTENDANT BACK-DOOR FRONTAL INTO THE AREA. WILL MAINTAIN CURRENT POP CONFIGURATION WITH HIGH CHANCE POPS ACROSS THE NORTH INVOF OF THE BETTER FORCING AND LOW CHANCE POPS SOUTH. A TOUCH COOLER ON FRIDAY AS HEIGHTS LOWER ALOFT COMBINED WITH AN INCREASE IN CLOUD COVER AND RAIN CHANCES. HIGHS IN THE LOWER 90S NORTH TO MID 90S SOUTH. LOWS FRIDAY NIGHT IN THE UPPER 60S TO LOWER 70S.
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&& .LONG TERM /SATURDAY THROUGH WEDNESDAY/...
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AS OF 300 AM THURSDAY... THE LONG TERM PERIOD WILL BE CHARACTERIZED BY A BUILDING UPPER RIDGE ACROSS THE MISSISSIPPI RIVER VALLEY WITH AN UPPER TROUGH/CLOSED LOW OFF THE NORTHEAST COAST...LEAVING CENTRAL NC UNDER A NORTHWESTERLY UPPER FLOW REGIME. THIS UPPER RIDGE IS PROGGED TO SHIFT EAST TOWARDS THE REGION BY THE MIDDLE OF NEXT WEEK. AS THE SURFACE...A BACKDOOR COLD FRONT WILL BE SLIPPING FURTHER TO OUR SOUTH AND WEST THROUGH THE DAY ON SATURDAY. DEEP MOISTURE WILL REMAIN ENTRENCHED OVER THE REGION THROUGH AT LEAST THE FIRST HALF OF THE WEEKEND AND GIVEN THIS SURFACE BOUNDARY AND ANY DISTURBANCES ALOFT WITHIN THE NORTHWESTERLY FLOW...PRECIP CHANCES WILL BE THE HIGHEST ON SATURDAY. THE DEEP MOISTURE BEGINS TO GET SHUNTED TO OUR SOUTHWEST ON SUNDAY...BUT ESPECIALLY INTO EARLY NEXT WEEK. THIS WILL RESULT IN DECREASING PRECIP CHANCES AND IN FACT HAVE REMOVED MENTION OF PRECIP FROM THE FORECAST BY THE EARLY TO MIDDLE PART OF NEXT WEEK...ESPECIALLY GIVEN THAT THE UPPER RIDGE WILL BUILD TOWARDS THE AREA. LOW LEVEL THICKNESS VALUES WILL GRADUALLY FALL THROUGH EARLY NEXT WEEK AS THE UPPER TROUGH DEEPENS DOWN THE WESTERN ATLANTIC. IN ADDITION...NORTHEASTERLY SURFACE FLOW WILL PERSIST AS HIGH PRESSURE RIDGES INTO THE AREA FROM THE NORTHEAST. ALL OF THIS WILL RESULT IN BELOW NORMAL TEMPS...WITH MID 80S TO NEAR 90 DEGREES ON SATURDAY AND UPPER 70S TO LOW/MID 80S EXPECTED FOR SUNDAY AND EARLY NEXT WEEK. TEMPS WILL BEGIN TO MODERATE TUESDAY AND ESPECIALLY INTO WEDNESDAY AS THE UPPER RIDGE SHIFTS EAST. OVERNIGHT LOWS WILL INITIALLY BE IN THE UPPER 60S TO LOWER 70S...WITH SLIGHTLY COOLER TEMPS FOR THE REMAINDER OF THE PERIOD (MOSTLY MID/UPPER 60S WITH SOME LOWER 60S IN THE COOLER LOCATIONS).
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&& .AVIATION /06Z THURSDAY THROUGH MONDAY/... AS OF 110 AM THURSDAY... SHORTWAVE VORT DISTURBANCE RESPONSIBLE FOR ONGOING AREA OF STORMS SURGING SOUTHWARD FROM SOUTHERN VA/NE NC IS IN THE PROCESS OF MOVING EAST AND OUT OF THE AREA. IF THESE STORMS HOLD TOGETHER...KRDU AND KRWI STAND THE BEST CHANCE OF SEEING SOME BRIEF RESTRICTIONS BETWEEN 06 TO 08Z. OTHERWISE...THE REMAINDER OF THE OVERNIGHT/EARLY MORNING HOURS ARE EXPECTED TO BE DRY WITH THE CHANCE FOR ALL TAF SITES TO SEE SOME VISIBILITY RESTRICTIONS FROM FOG DURING THE PRE-DAWN HOURS. FOG PRONE KRWI AND KRDU WHO SAW SIGNIFICANT/HEAVY RAINFALL THIS PAST EVENING COULD ONCE AGAIN SEE LIFR TO IFR RESTRICTIONS. ELSEWHERE MVFR VISBYS WILL BE FAVORED....UNLESS MORE PRECIP AFFECTS A GIVEN SITE. ANY SUB-VFR CONDITIONS WILL AGAIN LIFT TO VFR BY MID TO LATE MORNING AT THE LATEST... WITH THE PROSPECTS OF VFR CONDITIONS BY 13-15Z AT ALL TAF SITES FOR THURSDAY MORNING. ISOLATED TO WIDELY SCATTERED SHOWERS AND STORMS WILL BE POSSIBLE AGAIN ON THURSDAY ACROSS ALL OF CENTRAL NC. HOWEVER... THE PROBABILITY AT A GIVEN SITE IS TOO LOW TO INCLUDE IN THE TAFS AT THIS TIME. OUTLOOK... EARLY MORNING STRATUS/FOG...ALONG WITH AFTERNOON SHOWERS AND STORMS WILL BE POSSIBLE EACH DAY THIS WEEK. A BACKDOOR COLD FRONT WILL MOVE INTO THE AREA OVER THE WEEKEND...WHICH MAY BRING ANOTHER PERIOD UNSETTLED WEATHER FOR PORTIONS OF THE AREA. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...PWB NEAR TERM...CBL SHORT TERM...CBL LONG TERM...KRD AVIATION...CBL/BLS

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