Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 211447 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 1045 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 1045 AM WEDNESDAY... NORTHWEST FLOW CONTINUES ALOFT...THOUGH TODAY WITH LESS IN THE WAY OF A DISCERNIBLE FEATURE TO TRIGGER CONVECTION. THE PIEDMONT TROUGH IS SET UP OVER THE EASTERN PIEDMONT/COASTAL PLAIN...AND AREAS TO THE WEST WILL SEE MORE OF A WESTERLY FLOW AND BETTER MIXING. DRY ADIABATIC MIXING RESULTS IN HIGHS IN THE MID 90 MOST AREAS AND DEWPOINTS IN THE LOWER 60S WEST TO NEAR 70 EAST. THE LOWER DEWPOINTS SHOULD LIMIT MLCAPE TO AROUND 1000 J/KG OR LESS AND MAKE IT HARD FOR ANY CONVECTION IN THE MOUNTAINS TO MOVE INTO THE PIEDMONT. HOWEVER...A COUPLE HRRR RUNS HAVE HINTED AT SOME STORMS CONGEALING INTO A SMALL LINE...LIKELY AIDED BY EVAPORATIVE COOLING AND COLD POOL ENHANCEMENT. HOWEVER...THE MOST RECENT HRRR RUN HAS BACKED OFF ON THIS. WILL BE WATCHING SOME WEAK DISTURBANCES OVER EASTERN KY/TN TO SEE IF ANYTHING TRIGGERS....BUT FOR NOW POPS WILL BE LESS THAN 25 PERCENT. HEAT INDICES WILL BE 100-103 ROUGHLY EAST OF US 1. OVERNIGHT LOWS IN THE LOWER 70S.
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&& .SHORT TERM /FRIDAY AND FRIDAY NIGHT/... 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. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... 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). && .AVIATION /12Z THURSDAY THROUGH MONDAY/... AS OF 715 AM THURSDAY... 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. 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/BLS SHORT TERM...CBL LONG TERM...KRD AVIATION...CBL/BLS

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