Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 211746 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 145 PM 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 WILL MOVE SOUTH OF THE AREA ON SATURDAY. && .NEAR TERM /THROUGH TONIGHT/... 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. && .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 THURSDAY/... AS OF 145 PM THURSDAY... THE LONG TERM PERIOD REMAINS CHARACTERIZED BY A BUILDING UPPER RIDGE ACROSS THE MISSISSIPPI RIVER VALLEY WITH A DEEPENING UPPER TROUGH OFF THE EAST COAST...RESULTING IN A NORTHWEST UPPER FLOW REGIME ACROSS CENTRAL NORTH CAROLINA. AT THE SURFACE...A BACKDOOR COLD FRONT WILL MOVE SOUTH THROUGH THE AREA ON SATURDAY. DEEP MOISTURE WILL REMAIN ENTRENCHED OVER THE REGION THROUGH THE FIRST HALF OF THE WEEKEND. AS SUCH...THE BEST CHANCE OF PRECIPITATION WILL BE ON SATURDAY GIVEN THE SURFACE BOUNDARY AND POTENTIAL ADDITIONAL SUPPORT FROM DISTURBANCES ALOFT WITHIN THE NORTHWEST FLOW. THE UPPER TROF AXIS SHIFTS FURTHER OFFSHORE...ALLOWING DRIER AIR TO SURGE SOUTH AT THE MID LEVELS...WITH DEEPER MOISTURE SUPPRESSED SOUTHWEST OF THE AREA SUNDAY THROUGH THE MIDDLE OF NEXT WEEK. THE UPPER RIDGE WILL SHIFT EAST TO FURTHER AID IN DAMPENING CONVECTION AS WELL...SO PRECIP CHANCES WILL BE MINIMAL FROM MONDAY THROUGH THURSDAY. 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 FALLING INTO THE UPPER 70S TO LOW/MID 80S SUNDAY THROUGH TUESDAY. TEMPS WILL BEGIN TO MODERATE WEDNESDAY INTO THURSDAY AS THE UPPER RIDGE SHIFTS EAST. OVERNIGHT LOWS THIS WEEKEND WILL BE IN THE UPPER 60S TO LOWER 70S...WITH MID TO UPPER 60S MONDAY MORNING AND FOR THE REMAINDER OF THE WEEK. && .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...MLM AVIATION...CBL/BLS

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