Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 211838 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 235 PM EDT THU AUG 21 2014 .SYNOPSIS...
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A SERIES OF UPPER LEVEL DISTURBANCES WILL DIVE SOUTHEAST INTO OUR REGION FROM THE OHIO VALLEY AND MIDWEST. A COLD FRONT LOCATED ACROSS THE MID ATLANTIC ON FRIDAY WILL MOVE SOUTH THROUGH THE AREA OVER THE WEEKEND.
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&& .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/...
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AS OF 235 PM THURSDAY... FRIDAY WILL BE ANOTHER DAY WITH NORTHWESTERLY FLOW ALOFT...SURFACE TROUGHING IN THE EAST...AND THE POTENTIAL FOR A DISTURBANCE OR TWO TO CROSS THE AREA. THE MAIN DISTURBANCES IN QUESTION ARE LIKELY ASSOCIATED WITH CONVECTION OVER THE UPPER MIDWEST...AND ARE PROGGED TO MOVE SOUTHEAST ACROSS THE AREA LATE FRIDAY AFTERNOON. TIMING OF SUCH A FEATURE IS STILL TOUGH THIS FAR OUT...SO CONFIDENCE IN ITS ADDITIONAL SUPPORT FOR AFTERNOON CONVECTION IS LOW. DEEP MIXING IS EXPECTED AGAIN DURING THE AFTERNOON...WHICH WILL TEMPER INSTABILITY A LITTLE IN THE WEST WHERE DEWPOINTS SHOULD DROP BACK INTO THE MID 60S. THERMAL PROFILES ARE RELATIVELY SIMILAR TO TODAY...SO MLCAPE SHOULD AGAIN RANGE FROM LESS THAN 1000 J/KG IN THE WEST TO OVER 1500 J/KG IN THE EAST. A BELT OF STRONGER WESTERLIES OVER THE CENTRAL APPALACHIANS WILL LIKELY ENHANCE CONVECTION OVER VA...AND SOME OF THIS ACTIVITY MAY DRIFT SOUTH INTO THE NORTHERN PORTIONS OF THE CWA BY FRIDAY EVENING...SO WILL HAVE THE HIGHEST CHANCE POPS ACROSS THE NORTH...WHILE AREAS IN SOUTHERN PIEDMONT MAY STAY DRY. H85 TEMPS ARE FORECAST TO BE ABOVE 20C AGAIN FRIDAY AND WITH DEEP MIXING RESULTS IN MID TO POSSIBLY UPPER 90S. DEWPOINTS ARE FORECAST TO MIX OUT A LITTLE MORE IN THE EAST THAN TODAY...THOUGH ONLY SLIGHTLY...SO HEAT INDEX VALUES SHOULD AGAIN HOLD AROUND 100F IN THE SOUTHEAST. DEPENDING ON HOW MUCH CONVECTION THERE IS TO THE NORTH FRIDAY EVENING...THERE IS THE POTENTIAL FOR A WEAK EFFECTIVE FRONT INTO THE NORTHERN COASTAL PLAIN FRIDAY NIGHT...NECESSITATING POPS THROUGH THE OVERNIGHT HOURS. LOWS IN THE UPPER 60S TO LOWER 70S.
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&& .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 /18Z THURSDAY THROUGH TUESDAY/... AS OF 200 PM THURSDAY... VFR CONDITIONS ACROSS CENTRAL NC THIS AFTERNOON WITH A GENERALLY LIGHT WESTERLY WIND. A COUPLE WEAK DISTURBANCES WITHIN THE NORTHWESTERLY FLOW ALOFT WILL CROSS THE APPALACHIANS THIS EVENING...BUT THERE IS RELATIVELY LOW CONFIDENCE IN WHETHER OR NOT ADDITIONAL SHOWERS AND STORMS WILL BE ABLE TO MOVE EAST INTO THE PIEDMONT THIS AFTERNOON. TO THE EAST...WHERE INSTABILITY IS GREATEST...SOME WEAK CONVERGENCE MAY SUPPORT STORMS OVER THE COASTAL PLAIN...MOSTLY FROM KFAY TO KRWI AND EAST. HOWEVER...CONFIDENCE IS TOO LOW FOR MENTION IN THE CURRENT TAF. MOST OF ANY CONVECTION WILL DIE DOWN AFTER SUNSET...THOUGH MODELS SHOW THE POTENTIAL FOR SOME ADDITIONAL STORMS MOVING THROUGH SOUTHERN VA TO TRACK INTO THE NORTHERN COASTAL PLAIN OVERNIGHT. FOG AND STRATUS SHOULD AGAIN BE ISOLATED AND MOSTLY MVFR. OUTLOOK... A BACKDOOR COLD FRONT WILL MOVE INTO THE AREA OVER THE WEEKEND...BRINGING A PERIOD OF UNSETTLED WEATHER AND ADVERSE AVIATION CONDITIONS. DRIER WEATHER IS EXPECTED NEXT WEEK. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...BLAES NEAR TERM...CBL/BLS SHORT TERM...BLS LONG TERM...MLM AVIATION...BLS

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