Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 291307 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 907 AM EDT SAT AUG 29 2015 .SYNOPSIS...
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HIGH PRESSURE CONTINUES TO EXTEND OVER THE AREA FROM THE NORTH TODAY. AN UPPER LEVEL DISTURBANCE WILL MOVE NORTH ALONG THE APPALACHIANS ON SUNDAY.
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&& .NEAR TERM /THROUGH TONIGHT/...
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AS OF 905 AM SATURDAY... WHILE THE LATEST SURFACE ANALYSIS SHOWED HIGH PRESSURE OVER CENTRAL NORTH CAROLINA...AND SPC MESOANALYSIS DATA SHOWED LOW PRECIPITABLE WATER VALUES WITH AN 850MB RIDGE IN PLACE AND LIMITED 850MB MOISTURE ADVECTION...MID- AND HIGH-LEVEL CLOUDS WERE SPREADING OVER CENTRAL NORTH CAROLINA FROM THE SOUTH. THE LATEST WATER VAPOR IMAGES INDICATED THE INCREASE OF THE MID-LEVEL MOISTURE WELL...STREAMING NORTH AHEAD OF AN UPPER LOW OVER THE NORTHERN GULF. THE CANADIAN CLOUD COVER MODEL...WHICH SEEMED TO HAVE A GOOD HANDLE ON THE CLOUD COVER...SPREADS HIGH-LEVEL CLOUDS OVER CENTRAL NORTH CAROLINA FROM THE SOUTHWEST DURING THE DAY...WITH NUMEROUS CLOUDS EXPECTED EVEN OVER THE NORTHERN COASTAL PLAIN BY 18Z TO 20Z. EARLY MORNING VISIBLE IMAGES SUGGESTS THE INITIAL SURGE OF HIGH CLOUDS IS SOMEWHAT THIN...WHICH MAY PROVIDE FOR TIME FOR TEMPERATURES TO RECOVER. AS SUN BECOMES MORE FILTERED OVER TIME WITH LIKELY A GREATER DEGREE OF OPAQUE UPPER-LEVEL CLOUDS...THE EFFECT SHOULD DAMPEN THE TEMPERATURE RISE. STILL...DID NOT LOWER MAXES TOO MUCH...ONLY ABOUT A DEGREE OR SO...AS THERE MAY BE ENOUGH THIN SPOTS TO GET WARMING SUFFICIENT FOR ABOUT 10 TO 15 DEGREES OF TEMPERATURE INCREASE BEYOND THIS WRITING AT AN EARLY SUN TIME. RAP MODEL SOUNDINGS SHOW MOISTENING ONLY ALOFT...WITH DRY AIR BELOW 500MB AND A VERY CAPPED AIR MASS. TONIGHT...MID-HIGH LEVEL CLOUDS WILL THICKEN IN RESPONSE TO THE APPROACH OF THE NORTHERN GULF S/W THOUGH LIFT TO GENERATE ANY SHOWERS APPEARS TO BE LACKING. WEAK (EMPHASIS ON WEAK) LOW LEVEL ISENTROPIC LIFT MAY GENERATE A SHOWER OR SPRINKLES AROUND DAYBREAK OVER THE FAR SOUTHERN PIEDMONT. THE INCREASING CLOUDINESS AND A MODIFYING AIR MASS WILL YIELD MIN TEMPS A FEW DEGREES WARMER THAN LOW TEMPS EXPECTED THIS MORNING. MIN TEMPS MID 60S NORTH TO THE UPPER 60S SOUTH.
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&& .SHORT TERM /SUNDAY AND SUNDAY NIGHT/... AS OF 333 AM SATURDAY... HAVE TRENDED FORECAST THIS PERIOD A LITTLE WETTER...ESPECIALLY SUNDAY NIGHT ACROSS THE PIEDMONT AND SANDHILLS. ATMOSPHERE WILL CONTINUE TO MOISTEN AS NORTHERN GULF SYSTEM LIFTS NEWD ACROSS GA AND INTO THE SOUTHERN APPALACHIANS LATE IN THE DAY. THE APPROACH OF THIS SYSTEM WILL INDUCE A LOW LEVEL SELY FLOW...RESULTING IN AN UPSLOPE COMPONENT TO THE LOW LEVEL FLOW OVER THE SOUTHERN-WESTERN PIEDMONT. THE GFS SOLUTION IS A BIT MORE AGGRESSIVE WITH THIS SCENARIO COMPARED TO THE NAM WHILE THE 00Z ECMWF FAVORS THE GFS SOLUTION. INCREASING UPPER DIVERGENCE BY SUNDAY AFTERNOON IN CONJUNCTION WITH A SLIGHTLY UNSTABLE AND INCREASINGLY MOIST AIR MASS SHOULD SUPPORT THE DEVELOPMENT OF A FEW SHOWERS AND AN ISOLATED STORM...MAINLY ACROSS PORTIONS OF THE SOUTHERN PIEDMONT AND THE SANDHILLS. MAY SEE ADDITIONAL COVERAGE OVER THE SANDHILLS/SOUTHERN COASTAL PLAIN DUE TO THE INLAND MOVING SEABREEZE. THUS...WILL INCREASE POPS BIT FROM THE PREVIOUS FORECAST...UP TO 40 PERCENT OVER THE SOUTH AND WEST SECTIONS BY LATE IN THE DAY/SUNDAY EVENING. DUE TO EXPECTED EXTENSIVE CLOUDINESS...HAVE ADJUSTED MAX TEMPS DOWN A BIT OVER THE WEST AND SW...WITH LITTLE CHANGE ELSEWHERE. IF CLOUDS ARE LOWER/THICKER THAN EXPECTED OR SHOWER COVERAGE MORE EXTENSIVE BY AFTERNOON...MAX TEMPS MAY END UP BEING 3-4 DEGREES COOLER THAN FORECAST EVERYWHERE. SUNDAY NIGHT...S/W LIFTS NEWD IMMEDIATELY WEST OF OUR REGION LATE IN THE NIGHT...MAXIMIZING UPPER DIVERGENCE. IN THE 850-700MB LAYER WEAK SPEED CONVERGENCE IN THE MOIST LAYER. THUS...SHOULD SEE A THREAT FOR A FEW SHOWERS THROUGHOUT THE NIGHT...MAINLY ACROSS THE PIEDMONT. MIN TEMPS MAINLY IN THE UPPER 60S TO NEAR 70. && .LONG TERM /MONDAY THROUGH FRIDAY/... AS OF 355 AM SATURDAY... THE MODELS ARE IN BETTER AGREEMENT TODAY REGARDING THE EJECTION/PROGRESSION OF A SHORTWAVE TROUGH --INITIALLY A CLOSED LOW OVER THE CENTRAL GULF COAST THIS MORNING-- FROM THE CENTRAL APPALACHIANS TO THE MIDDLE ATLANTIC COAST ON MON. MEANWHILE...AN UPSTREAM KICKER SHORTWAVE TROUGH WILL AMPLIFY INTO THE SOUTHERN PLAINS TO LOWER AND MID MS VALLEY AND RE-CARVE THE TROUGH WESTWARD...AND CONSEQUENTLY ALLOW THE SUB-TROPICAL RIDGE TO BULGE WESTWARD INTO THE SOUTHEAST US. A STRONGLY POSITIVELY-TILTED SHEAR AXIS WILL SEPARATE THE SOUTHEASTERN RIDGE AND ANOTHER FORECAST TO BUILD ACROSS THE OH VALLEY AND GREAT LAKES...AND THIS FEATURE WILL INITIALLY DRAW TROPICAL MOISTURE ASSOCIATED WITH (AND IN ADVANCE OF) ERIKA...NORTHWARD THROUGH THE CAROLINAS EARLY NEXT WEEK. THEREAFTER...MOISTURE FROM (AND THE OVERALL INFLUENCE OF) ERIKA...WILL BE DEPENDENT ON HOW ERIKA EVOLVES DURING THE NEXT SEVERAL DAYS...WHICH IS A RELATIVELY LOW CONFIDENCE FORECAST. THE ENVELOPE OF GUIDANCE SOLUTIONS HAS CONTINUED A WESTWARD TREND WITH THE TRACK OF WHAT BECOMES OF ERIKA...WITH THE PREFERRED NHC TRACK NOW THROUGH THE EASTERN GULF OF MEXICO/ALONG THE WEST COAST OF FL EARLY NEXT WEEK...TO A POSITION NEAR THE FL PANHANDLE OR SOUTHERN GA BY WED. CONSIDERABLE FORECAST UNCERTAINTY REMAINS WITH ERIKA... HOWEVER...SINCE THE CIRCULATION MAY DISSIPATE ALTOGETHER DUE TO THE INTERACTION WITH BOTH LAND AND A HOSTILE WIND SHEAR ENVIRONMENT DURING THE NEXT 24-36 HOURS. OR IF IT SURVIVES... REGENERATION/ STRENGTHENING WILL BE POSSIBLE OVER THE WARM WATERS AND IN A WEAKENING WIND SHEAR ENVIRONMENT OVER THE FL STRAITS AND EASTERN GOM. REGARDLESS...IT STILL APPEARS THAT THE LOW LEVEL VORTICITY CENTER...IN WHATEVER STATE IT MAY BE BY THE MIDDLE OF NEXT WEEK...WILL LIKELY BE SUPPRESSED MOSTLY SOUTH AND/OR WEST OF CENTRAL NC BY THE MERGING OF THE AFOREMENTIONED RIDGES ALOFT FROM THE GREAT LAKES TO THE SE COAST. AS SUCH...OUR SENSIBLE WEATHER WILL LIKELY INSTEAD BE INFLUENCED INDIRECTLY BY ASSOCIATED MOISTURE STREAMING NNE ALONG THE AFOREMENTIONED SHEAR AXIS...WHICH WOULD RESULT IN BOTH VARIABLY CLOUDY CONDITIONS AND SUPPORT FOR SLIGHTLY ABOVE CLIMO PRECIPITATION CHANCES - HIGHEST SOUTH IN CLOSEST PROXIMITY TO THE REMNANTS OF ERIKA. TEMPERATURES SHOULD BE CLOSE TO CLIMO - PERHAPS A LITTLE BELOW /ABOVE FOR HIGHS/LOWS DEPENDING ON TIMING AND EXTENT OF MOISTURE/CLOUD COVER. && .AVIATION /12Z SATURDAY THROUGH WEDNESDAY/... AS OF 640 AM SATURDAY... THERE IS A HIGH PROBABILITY OF VFR CONDITIONS PERSISTING ACROSS CENTRAL NC THROUGH EARLY SUNDAY. HIGH PRESSURE CENTERED OVER THE NORTHERN MID ATLANTIC WILL EXTEND SOUTH INTO CENTRAL NC...CAUSING THE VFR CONDITIONS. A DECK OF HIGH CLOUDS WILL PREVAIL LATER TODAY AND TONIGHT WITH BASES ABOVE 10K FEET. SFC WINDS WILL BE GENERALLY LIGHT AND VARIABLE THOUGH KFAY AND KRWI SHOULD SEE A PREDOMINATE EAST-NE SFC WIND LATER THIS MORNING THROUGH EARLY AFTERNOON... BETWEEN 7-10KTS. WHILE VFR CONDITIONS WILL LIKELY CONTINUE INTO EARLY NEXT WEEK...THERE WILL BE A THREAT FOR SCATTERED CONVECTION SUNDAY THROUGH MONDAY AS AN UPPER DISTURBANCE LIFTS NWD ACROSS THE CAROLINAS FROM THE DEEP SOUTH. MVFR CEILINGS/VISIBILITY COULD OCCUR IN VICINITY OF THE CONVECTION. THE AIR MASS WILL BECOME INCREASINGLY MOIST AND UNSTABLE TUESDAY AND WEDNESDAY...SUGGESTING A BETTER CHANCE FOR PERIODS OF MVFR/IFR CEILINGS DUE TO STRATUS IN THE OVERNIGHT-EARLY MORNING HOURS...AND SCATTERED CONVECTION. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...DJF/WSS NEAR TERM...DJF/WSS SHORT TERM...WSS LONG TERM...26 AVIATION...WSS

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