Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 231853 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 250 PM EDT SAT AUG 23 2014 .SYNOPSIS...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. && .NEAR TERM /THROUGH SUNDAY/... 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. && .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 THROUGH SATURDAY/...
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AS OF 250 PM SATURDAY... FOR MONDAY THROUGH MID-WEDNESDAY...LOOK FOR FAIR WEATHER WITH NEAR- TO SLIGHTLY-BELOW NORMAL TEMPS (HIGHS IN THE LOW-MID 80S AND LOWS IN THE LOW 60S) AS HIGH PRESSURE BUILDS IN TO THE CAROLINAS FROM THE NORTH EARLY IN THE WEEK AND REMAINS OVER OUR AREA THROUGH MID-WEEK. FORECAST SOUNDINGS SUGGEST PWAT WILL RANGE FROM 0.5-1.0 INCHES DURING THIS TIME...WHICH IS WELL BELOW THE 1.35 INCH NORM FOR LATE AUGUST. A LARGE DEGREE OF UNCERTAINTY EXISTS FOR THE SECOND HALF OF THE WEEK...AS THIS PART OF THE FORECAST IS LARGELY DEPENDENT ON WHAT HAPPENS WITH INVEST 96L. TRACK MODELS HAVE BEEN QUITE SCATTERED AND LITTLE AGREEMENT AMONG THE GEFS/NAEFS MEMBERS. HOWEVER...ITS WORTH NOTING THAT THE TREND IN THE OPERATIONAL GFS HAS BEEN DEVELOPMENT AND SLOW NORTHWARD MOVEMENT E OF FL DURING THE FIRST HALF OF THE WEEK...THEN MOVING NNE ALONG BUT REMAINING OFF THE CAROLINA COAST LATE IN THE WEEK. THE LATEST ECMWF IS SIMILAR WITH THE EVOLUTION OF THIS SYSTEM...BUT IS FASTER AND ITS TRACK REMAINS FURTHER OFF THE COAST...SHOWING THE LOW MOVING NE AWAY FROM THE EAST COAST ON THURSDAY. ESSENTIALLY BOTH OF THESE SOLUTIONS WOULD KEEP CENTRAL NC FAR ENOUGH WEST OF THE SYSTEM SUCH THAT OUR AREA WOULD REMAIN IN FAIR WEATHER DURING THE SECOND HALF OF THE WEEK. TAKING THAT SYSTEM OUT OF THE PICTURE...OUR NEXT CHANCE FOR WET WEATHER WOULD COME DURING THE WEEKEND ASSOCIATED WITH EITHER THE NEXT TROUGH IN THE WESTERLIES (PER GFS) OR INCREASING MOISTURE IN THE RETURN FLOW AROUND THE RIDGE (PER THE ECWMF). IN SUMMARY...LOTS OF UNCERTAINTY FOR THE SECOND HALF OF THE LONG TERM...SO WILL STICK CLOSE TO CLIMO FOR TEMPS AND PERHAPS A LITTLE LOWER THAN CLIMO FOR POPS DURING THIS TIME.
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&& .AVIATION /18Z SATURDAY THROUGH WEDNESDAY/... AS OF 225 PM SATURDAY... AS OF 18Z...SOME MVFR CONDITIONS MAINLY ASSOCIATED WITH CIGS PERSIST ACROSS PARTS OF THE NORTHEAST PIEDMONT AND COASTAL PLAIN. ELSEWHERE VFR CONDITIONS WITH MULTIPLE LOW TO MID CLOUD LAYERS ARE OBSERVED. SCATTERED SHOWERS AND THUNDERSTORMS WILL BECOME MORE NUMEROUS AND MOVE SOUTHEAST THIS AFTERNOON AND EVENING ACROSS CENTRAL NC AS A COLD FRONT AND AN UPPER LEVEL DISTURBANCE TRIGGERS AND THEN MAINTAIN SCATTERED CONVECTION. INITIALLY THE PRECIPITATION WILL BE MOST WIDESPREAD THIS AFTERNOON ACROSS THE COASTAL PLAIN...MAINLY EAST OF THE KRWI AND KFAY TERMINALS. ANOTHER AREA OF SHOWERS AND THUNDERSTORMS WILL ROTATE AND PUSH SOUTH ACROSS THE NORTHERN PIEDMONT THIS AFTERNOON AND THEN GRADUALLY SHIFT SOUTH LATER THIS AFTERNOON AND ESPECIALLY THIS EVENING. THE CONVECTION WILL TEND TO SHIFT SOUTH...WEAKEN AND DECREASE IN COVERAGE LATER THIS EVENING AND OVERNIGHT. EXPECT LOCAL REDUCTIONS TO MVR AND INTERMITTENTLY IFR CONDITIONS IN SHOWERS AND THUNDERSTORMS. PREVAILING CEILINGS WILL ALSO DECREASE OVERNIGHT AS COOLER AIR MOVES INTO THE REGION WITH PERIODS OF IFR CONDITIONS IN LOW CLOUDS AND SOME FOG LIKELY TOWARD DAYBREAK WITH HEATING AND AN INFLUX OF DRIER AIR FROM THE NORTHEAST...CEILINGS SHOULD LIFT A COUPLE OF HOURS AFTER DAYBREAK WITH VFR CONDITIONS PREVAILING BY LATE OR EARLY AFTERNOON. LOOKING FURTHER AHEAD...HIGH PRESSURE AT THE SURFACE AND ALOFT WILL EXTEND INTO THE REGION FOR THE LATE SUNDAY THROUGH WEDNESDAY PERIOD BRINGING A PERIOD OF GENERALLY FAIR WEATHER. EXCEPTIONS WOULD INCLUDE THE POTENTIAL FOR SOME DAYBREAK FOG ON MONDAY AND TUESDAY MORNINGS...ESPECIALLY ACROSS THE COASTAL PLAIN AND PERHAPS A SHOWER ACROSS THE EASTERN SECTIONS IN A PERSISTENT NORTHEAST FLOW. -BLAES && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...BLAES NEAR TERM...BLAES/BSD SHORT TERM...WSS LONG TERM...NP AVIATION...BLAES

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