Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 201420 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 1015 AM EDT WED AUG 20 2014 .SYNOPSIS...A SERIES OF UPPER LEVEL DISTURBANCES IN NORTHWEST FLOW ALOFT WILL CROSS THE REGION THIS WEEK. A BACK DOOR COLD FRONT IS FORECAST TO SLIP INTO THE AREA OVER THE WEEKEND. && .NEAR TERM /THROUGH TONIGHT/... AS OF 1015 AM WEDNESDAY... THE OVER ALL WEATHER PATTERN STILL CONSISTS OF RELATIVELY WEAK NORTHWESTERLY FLOW ALOFT AND A BROAD TROUGH AT THE SURFACE. IS SLOWLY ERODING THIS MORNING...THOUGH AREAS NORTH OF HWY 64 ARE STILL ENSHROUDED IN STRATUS. UPSTREAM...AN UPPER LEVEL TROUGH MOVING THROUGH THE CENTRAL APPALACHIANS IS AIDING A BROKEN LINE OF SHOWERS AND STORMS...WHICH HAS ACTUALLY HELD TOGETHER PRETTY WELL ON THE SOUTHERN END NEAR THE BLUE RIDGE. THE WEAK VORT LOBE WITH THIS TROUGH WILL CROSS THE CWA THIS AFTERNOON. LINGERING STRATUS WILL DELAY BETTER DESTABILIZATION...BUT RADAR TRENDS SUGGEST THE SHOWERS AND STORMS MAY HOLD TOGETHER THROUGH AT LEAST THE TRIAD AREA INITIALLY. WITH ADDITIONAL HEATING...FORECAST SOUNDINGS GIVE 1000- 1500 J/KG MLCAPE THIS AFTERNOON...THOUGH THE NAM/GFS VALUES ARE VERY SENSITIVE TO HIGHER/LOWER DEWPOINTS. IN FACT...THE NAM FORECAST SOUNDINGS AT KINT/KGSO HAVE A DEWPOINT OF 70F AND MLCAPE OVER 2000 J/KG THIS AFTERNOON. THIS SEEMS OVERDONE GIVEN SREF CONSENSUS. ALSO ACCOMPANYING THE AFOREMENTIONED SHORTWAVE IS A RIBBON OF EFFECTIVE DEEP SHEAR OF UP TO 30KT...SO IF CONVECTION CAN REINTENSIFY OVER THE PIEDMONT BY EARLY AFTERNOON...A FEW STRONG TO SEVERE STORM CLUSTERS COULD BE POSSIBLE. WILL INCREASE POPS OVER THE NORTHWEST PIEDMONT THROUGH MIDDAY...WITH A CHANCE ACROSS THE NORTH THIS AFTERNOON AND A SLIGHT CHANCE ACROSS THE SOUTH. HIGHS IN THE UPPER 80S TO LOWER 90S. LOWS TONIGHT IN THE UPPER 60S TO LOWER 70S. && .SHORT TERM /THURSDAY AND THURSDAY NIGHT/... AS OF 245 AM WEDNESDAY... LITTLE CHANGE ON THE SYNOPTIC PATTERN ON THURSDAY. CENTRAL NC WILL REMAIN POISED TO SEE VORT DISTURBANCES EMBEDDED IN THE NW FLOW ALOFT AS THE UPPER LOW OVER THE GREAT LAKES WEAKENS THROUGH THE DAY AS IT MOVES EAST INTO THE NE US. AT THIS TIME...CAN NOT FIND A DISCERNIBLE FEATURE THAT WOULD SUPPORT MORE THAN ISOLATED SLIGHT CHANCE POPS THURSDAY/THURSDAY NIGHT...IN FACT...500MB HEIGHTS ACTUALLY INCREASE OVER THE AREA ON THURSDAY...WITH ASSOCIATED SUBSIDENCE/WARMING ALOFT POSSIBLY SUPPRESSING CONVECTION TO A POINT WHERE IT COULD END UP BEING ONE OF THE LEAST CONVECTIVELY ACTIVE DAYS OF THE WEEK. AS FAR AS TEMPERATURES...BOTH THE EC AND GFS INDICATE H8 TEMPERATURES WILL WARM TO 22C...WHICH SHOULD SUPPORT HIGHS THURSDAY SOLIDLY IN THE MID 90S. LOWS THURSDAY NIGHT IN THE LOWER 70S. && .LONG TERM /FRIDAY THROUGH TUESDAY/... AS OF 245 AM WEDNESDAY... 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. DIFFERENCES REMAIN AMONG THE MODELS WITH RESPECT TO THE EVOLUTION OF THE UPPER AIR PATTERN...ESPECIALLY BY EARLY NEXT WEEK. REGARDLESS...GIVEN THAT MUCH OF OUR PRECIP CHANCES WILL HINGE ON DISTURBANCES ALOFT WITHIN THE NORTHWEST FLOW AND THAT THE PRECISE TIMING OF ANY SUCH DISTURBANCES THIS FAR OUT IS NEARLY IMPOSSIBLE... CONFIDENCE IN THE EXACT DETAILS OF PRECIP CHANCES ARE RATHER LOW. AS A SHORTWAVE TROUGH TRACKS OFF THE NORTHEASTERN US COAST (AND EVENTUALLY TRANSITIONS INTO A CLOSED LOW/DEEP TROUGH JUST OFF THE EAST COAST THROUGH EARLY NEXT WEEK)...A BACKDOOR COLD FRONT WILL BE PUSHED THROUGH THE AREA FRIDAY. THIS SHOULD LEAD TO SOLID CHANCE POPS. MODELS HAVE BACKED OFF ON DRIER AIR FILTERING IN BEHIND THE FRONT AND THEREFORE PRECIP CHANCES WILL REMAIN IN THE FORECAST THROUGH AT LEAST EARLY NEXT WEEK GIVEN THE PERSISTENT NORTHWEST FLOW REGIME AND SUBSEQUENT "TRAIN" OF DISTURBANCES ALOFT TRACKING ACROSS THE AREA. THERE ARE SOME INDICATIONS THAT THE UPPER RIDGE MAY BUILD FAR ENOUGH EAST BY THE VERY END OF THE LONG TERM PERIOD WHICH WOULD RESULT IN DECREASING PRECIP CHANCES. TEMPS ON FRIDAY ARE EXPECTED TO BE IN THE LOW TO MID 90S...WITH SLIGHTLY "COOLER" TEMPS FOR THE WEEKEND AND EARLY NEXT WEEK AS HEIGHTS FALL WHILE THE DEEP UPPER TROUGH BUILDS DOWN THE WESTERN ATLANTIC...WITH MAINLY 80S EXPECTED. TEMPS MAY BEGIN TO REBOUND SOME BY TUESDAY IF THE UPPER RIDGE DOES INDEED START TO BUILD EAST. OVERNIGHT LOWS WILL GENERALLY IN THE UPPER 60S TO LOWER 70S THROUGHOUT THE PERIOD. && .AVIATION /12Z WEDNESDAY THROUGH SUNDAY/... AS OF 720 AM WEDNESDAY... RAP SOUNDINGS SUGGEST FOG/STRATUS ACROSS THE NORTHEAST PIEDMONT AND NORTHERN COASTAL PLAIN WILL DISSIPATE BETWEEN 13-15Z. SHORTWAVE DISTURBANCES TRAVERSING THE REGION WILL ONCE AGAIN FUEL ISOLATED TO SCATTERED CONVECTION THIS AFTERNOON/EVENING... WITH THE HIGHEST PROBABILITY ACROSS THE NORTHERN TAF SITES. HOWEVER... CONFIDENCE IS NOT HIGH ENOUGH TO INCLUDE ANY MENTION OF CONVECTION IN THE TAFS AT THIS TIME. WILL FOLLOW PERSISTENCE WRT FOG TONIGHT...DEVELOPING ACROSS THE AREA BETWEEN 06 TO 12Z. OUTLOOK... EARLY MORNING STRATUS/FOG...ALONG WITH AFTERNOON SHOWERS AND STORMS WILL BE POSSIBLE EACH DAY THIS WEEK INTO THE WEEKEND. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...BLS NEAR TERM...CBL/BLS SHORT TERM...CBL LONG TERM...KRD AVIATION...CBL/BLS

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