Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 231505 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 1100 AM EDT SAT AUG 23 2014 .SYNOPSIS...
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A COLD FRONT WILL MOVE SOUTH ACROSS SOUTHERN VIRGINIA AND NORTH CAROLINA THIS AFTERNOON AND TONIGHT. HIGH PRESSURE WILL BUILD SOUTH INTO THE REGION WITH COOLER AND DRIER CONDITIONS EARLY NEXT WEEK.
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&& .NEAR TERM /THROUGH SUNDAY/...
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AS OF 1100 AM SATURDAY... LATEST SURFACE ANALYSIS REVEALS A COMPLEX PATTERN WITH THE BACK DOOR COLD FRONT NOW EXTENDING ACROSS NORTHEAST NC INTO SOUTHWESTERN VA AS WELL AS A SURFACE TROUGH EXTENDING ALONG THE NC/SC COAST WITH A WEAK SURFACE LOW CENTERED NEAR KILM. THE MAIN SURGE OF COLDER/DRIER AIR LAGS BEHIND THE FRONT AND IS LOCATED ACROSS EASTERN PA AND THE NORTHERN CHESAPEAKE BAY. A NORTHWEST FLOW DOMINATES THE MID AND UPPER AIR PATTERN ACROSS THE CAROLINAS WITH A STRENGTHENING NORTHERN STREAM JET POISED TO DROP INTO THE MID ATLANTIC THIS AFTERNOON...NOTE THE 105KT JET AT 200 HPA AT KIAD THIS MORNING. THE AIRMASS ACROSS THE REGION IS RATHER MOIST WITH PW VALUES OF 120-135% OF NORMAL AT KGSO/KMHX RESPECTIVELY. WITH THE ENHANCED FLOW ALOFT AND MULTIPLE MECHANISMS FOR LOCAL CONVERGENCE...NOT SURPRISED THAT HIGH RESOLUTION GUIDANCE SUGGESTS FAIRLY DECENT CONVECTIVE COVERAGE FOR THIS AFTERNOON. SHOWERS HAVE ALREADY BEGUN TO BLOSSOM IN SOUTHERN VA IN PROXIMITY TO THE SURFACE FRONT AND A DISTURBANCE IN THE NW FLOW ALOFT. OTHER CONVECTION IS BUBBLING UP IN THE COASTAL PLAIN AND COASTAL REGION NEAR THE SURFACE TROUGH. USED A BLEND OF HRRR AND RAP HOURLY PRECIP FIELDS TO GENERATE THE HOURLY POP/QPF/WX GRIDS THIS AFTERNOON. WHILE CONVECTIVE COVERAGE IS EXPECTED TO BE SOMEWHAT GENEROUS...ONLY A WEAKLY UNSTABLE AIRMASS WITH MLCAPE VALUES LESS THAN 1000 SHOULD MINIMIZE OVERAL INTENSITY. THE BEST FLOW ALOFT SHOULD REMAIN IN THE VA/MD/DE REGION WITH BULK SHEAR VALUES IN OUR CWA CLIMBING TO AROUND 2 5KTS. THE BIGGER THREAT WILL LIKELY BE ASSOCIATED WITH LOCALLY HEAVY RAIN WITH CELLS ORIENTED IN THE NW FLOW THAT REPEATEDLY MOVE OVER A GIVEN AREA. CLOUD COVER AND SCT CONVECTION SHOULD HOLD TEMPERATURES DOWN A BIT...ESPECIALLY IN THE NORTHEAST. A LITTLE BIT MORE SUNSHINE ACROSS THE SOUTHERN PIEDMONT AND SANDHILLS SHOULD ALLOW TEMPERATURES TO WARM TO AROUND OR JUST ABOVE 90. -BLAES MAIN AREA OF CONVECTION IS FORECAST TO BEGIN PUSHING TO THE SOUTH OF THE AREA BY THIS EVENING... WHILE THE LOW LEVEL FRONTAL ZONE BEGINS TO MOVE INTO THE AREA. THIS SHOULD YIELD A CONTINUED LOW END CHANCE OF AT LEAST SOME SHOWERS THOUGH. WITH A LOW LEVEL EAST TO NORTHEASTERLY FLOW TONIGHT... LOW STRATUS IS APT TO DEVELOP... WITH PATCHY LIGHT DRIZZLE EVEN. THE MAIN PUSH OF THE COOLER AIR SHOULD HOLD OFF UNTIL AFTER DAYBREAK SUNDAY. THUS... EXPECT LOW TEMPS WILL BE IN THE UPPER 60S TO LOWER 70S. SUNDAY: SURFACE HIGH PRESSURE WILL CONTINUE TO BUILD INTO THE AREA ON SUNDAY... ALONG WITH DRIER AIR ALOFT. THIS WILL YIELD MUCH DRIER CONDITIONS ON SUNDAY... WITH SKIES BECOMING PARTLY SUNNY BY AFTERNOON. HIGH TEMPS WILL BE COOLER... AROUND 80 NORTHEAST TO MID 80S SOUTH/SOUTHWEST. CAN`T RULE OUT SOME LIGHT SHOWERS IN THE EAST TO EAST-NORTHEASTERLY LOW LEVEL FLOW IN THE MORNING TO EARLY AFTERNOON THOUGH.
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&& .SHORT TERM /SUNDAY NIGHT AND MONDAY/... AS OF 306 AM SATURDAY... SURFACE DRY AIR RIDGE EXTENDS SOUTHWARD INTO NC FROM A PARENT HIGH POSITIONED OVER NORTHERN MID ATLANTIC. THIS SURFACE RIDGE SUPPORTED ALOFT BY A BUILDING UPPER LEVEL RIDGE...STRETCHING FROM THE MID- LOWER MS VALLEY NEWD INTO NEW ENGLAND. NELY LOW LEVEL FLOW WILL ADVECT COOLER DRIER AIR INTO CENTRAL NC. THIS DRIER AIR WILL AID TO DIMINISH ANY RESIDUAL STRATOCU. LOW LEVEL THICKNESSES DROP TO VALUES 15-20M BELOW NORMAL FOR LATE AUGUST. THIS YIELDS MAX TEMPS OF NEAR 80 ACROSS THE FAR NORTH-NW TO LOW/MID 80S FAR SOUTH. MIN TEMPS SUNDAY NIGHT LOW-MD 60S. && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... AS OF 306 AM SATURDAY... MONDAY NIGHT THROUGH THURSDAY...TRANQUIL WEATHER PATTERN WILL CONTINUE. UPPER LEVEL RIDGE WILL REMAIN HIGHLY AMPLIFIED UNTIL LATE WEDNESDAY INTO THURSDAY AT WHICH TIME A S/W IN THE NORTHERN STREAM WILL BE EXITING THE NORTHERN PLAINS INTO THE GREAT LAKES. THE APPROACH OF THIS SYSTEM WILL WEAKEN/SUPPRESS THE UPPER RIDGE SOUTHWARD. ASSOCIATED SFC RIDGE WILL MAINTAIN A DRY WEATHER REGIME WITH MODERATING TEMPERATURES THROUGH THURSDAY. MAX TEMPS TUESDAY NEAR 80 NORTH TO LOWER 80S SOUTH WARM TO THE MID-UPPER 80S BY THURSDAY. MIN TEMPS ALSO GRADUALLY MODIFY...FROM THE UPPER 50S-LOWER 60S TUESDAY MORNING TO THE MID 60S THURSDAY MORNING. FORECAST CONFIDENCE WANES THURSDAY INTO FRIDAY AS GFS IS MUCH FASTER WITH THE APPROACH OF THE NORTHERN STREAM S/W TOWARD THE EAST COAST VERSUS THE SLOWER ECMWF. ALSO OF CONCERN IS THE EVENTUAL TRACK OF THE TROPICAL SYSTEM THAT IS EXPECTED TO TRACK PARALLEL BUT OFFSHORE OF THE SE U.S. COAST. LATEST MODEL GUIDANCE (MAINLY ECMWF) HAS SHIFTED A LITTLE MORE TO THE WEST...WITH MAJOR TIMING DIFFERENCES (ECMWF MUCH FASTER COMPARED TO THE GFS). WITH THE TROPICAL SYSTEM OFFSHORE AND A TROUGH IN THE VICINITY OF THE GREAT LAKES/MID MS VALLEY...WOULD EXPECT A NARROW RIDGE OVER THE CAROLINAS. UNTIL THE DIFFERENCES ARE RESOLVED...FAVOR A WARM AND MAINLY DRY FORECAST FOR THE END OF THE WORK WEEK. HAVE WARMED TEMPS INTO THE MID 80-AROUND 90 FOR MAX TEMPS FRIDAY WHILE DECREASED RAIN CHANCE TO SLIGHT CHANCE. && .AVIATION /11Z SATURDAY THROUGH WEDNESDAY/... AS OF 655 AM SATURDAY... A FEW LIGHT ISOLATED TO LOCALLY SCATTERED SHOWERS CONTINUE TO MOVE ACROSS NORTHEAST PORTIONS OF CENTRAL NC THIS MORNING... POSSIBLY AFFECTING KRDU AND KRWI FOR THE NEXT COUPLE OF HOURS. HOWEVER... CONDITIONS ARE GENERALLY EXPECTED TO REMAIN VFR WITH THESE SHOWERS. GREATER CONVECTIVE COVERAGE IS EXPECTED LATER THIS MORNING INTO THE AFTERNOON AS A SERIES OF UPPER LEVEL DISTURBANCES TRACK S/SSE ACROSS THE CAROLINAS AND A BACK DOOR COLD FRONT/PRE-FRONTAL TROUGH PROGRESSES TOWARDS CENTRAL NC FROM THE N/NE. THUS... WILL MENTION A TEMPO GROUP FOR SHOWERS AND SUB-VFR CONDITIONS IN THE TAFS FOR THE AFTERNOON. THUNDERSTORMS WILL BE POSSIBLE AS WELL... BUT WILL HOLD OFF ADDING THUNDER UNTIL WE HAVE A HIGHER CONFIDENCE THAT A GIVEN LOCATION WILL BE AFFECTED BY A THUNDERSTORM. THE STRONGEST STORMS WILL HAVE THE POTENTIAL TO PRODUCE IFR/LIFR VISBYS AND STRONG WIND GUSTS. IFR TO POSSIBLY EVEN LIFR CEILINGS WILL BE POSSIBLE IN THE WAKE OF THE BACKDOOR COLD FRONT TONIGHT THROUGH MID-DAY SUNDAY...THOUGH COVERAGE AND DURATION REMAIN A BIT UNCERTAIN (HIGHEST CONFIDENCES OF SUB-VFR CONDITIONS AT KGSO/KINT). AN UPPER LEVEL RIDGE CENTERED IN VICINITY OF THE SOUTHERN APPALACHIANS SHOULD RESULT IN BETTER-THAN- NORMAL CHANCES FOR VFR CONDITIONS MON-WED...THOUGH A PERSISTENT E/NE LOW-LEVEL FLOW MAY ALLOW ADEQUATE MOISTURE FOR LOW-TOPPED SHOWER ACTIVITY...ESP AT THE EASTERN TERMINALS (FAY/RWI). && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...BLAES NEAR TERM...BLAES/BSD SHORT TERM...WSS LONG TERM...WSS AVIATION...BSD/VINCENT

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