Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 271959 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 255 PM EST SAT DEC 27 2014 .SYNOPSIS...HIGH PRESSURE OVERHEAD THIS MORNING WILL SHIFT EAST OF THE AREA BY TONIGHT. A COLD FRONT WILL APPROACH FROM THE NORTHWEST ON SUNDAY... AND GRADUALLY MOVE SOUTHWARD THROUGH THE REGION ON MONDAY. && .NEAR TERM /TONIGHT THROUGH SUNDAY/...
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AS OF 255 PM SATURDAY.. LATEST SURFACE ANALYSIS SHOWS AN AREA OF SURFACE HIGH PRESSURE CENTERED NEAR THE NC/SC COAST ALONG THE COASTAL CAROLINAS AND VIRGINIA. A POSITIVELY TILTED DEAMPLIFYING UPPER TROUGH ACROSS THE WESTERN PLAINS AT MIDDAY TODAY WILL CONTINUE TO SHIFT SLOWLY EAST TODAY AND TONIGHT. THE NORTHERN PORTION OF THE TROUGH ASSOCIATED WITH THE NORTHERN JET STREAM WILL SHEAR EAST INTO THE EASTERN GREAT LAKES WHILE BY LATE SUNDAY AFTERNOON. THE SOUTHERN EXTENT OF THE TROUGH IS SHARPER AND MOVES SLOWLY EAST REACHING THE ARKLATEX BY SUNDAY EVENING. THE ASSOCIATED COLD FRONT WHICH EXTENDS FROM MICHIGAN SOUTHWEST TO EASTERN TX AT MIDDAY TODAY WILL MOVE EAST REACHING EASTERN PA AND NORTHWEST GA BY LATE SUNDAY AFTERNOON. MAINLY CLEAR SKIES ACROSS CENTRAL NC THIS AFTERNOON WILL GIVE WAY TO INCREASING HIGH AND MID CLOUDINESS THIS EVENING AS MOISTURE BEGINS TO INCREASE AHEAD OF THE FRONT. WHILE HIGH AND MID LEVEL CLOUDINESS WILL THICKEN OVERNIGHT... NAM/GFS/SREF BUFR SOUNDINGS ALL NOTE THAT THE LOWER THIRD OF THE TROPOSPHERE IS SLOW TO MOISTEN OVERNIGHT UNTIL LOW LEVEL MOISTURE SURGES INTO THE REGION FROM THE SOUTHWEST TOWARD DAYBREAK SUNDAY. THE PRECIPITATION IS LARGELY DRIVEN BY ISENTROPIC LIFT AROUND THE 295K SURFACE WITH THE BEST SURGE OF LIFT SKIRTING ACROSS THE NORTHWESTERN EDGE OF CENTRAL NC AND WILL ADVERTISE LOW CATEGORICAL POPS THERE. FORCING FOR ASCENT DECREASES TO THE SOUTH AND EAST ON SUNDAY WITH LOW CHANCE POPS ADVERTISED FOR THE SANDHILLS AND SOUTHERN COASTAL PLAIN. SO SUNDAY WILL FEATURE CLOUDY SKIES ACROSS CENTRAL NC IT WONT BE WASHOUT FOR EVERYONE. MAINLY SPOTTY LIGHT RAIN IS EXPECTED TO THE SOUTH AND SOUTHEAST OF RALEIGH WITH THE MOST WIDESPREAD RAIN EXPECTED NEAR AND ESPECIALLY TO THE NORTHWEST OF INTERSTATE 85. TEMPERATURES WILL BE A LITTLE TRICKY AS THEY WILL TEND TO FALL QUICKLY THIS EVENING AFTER SUNSET BUT THE OVERNIGHT TREND WILL BE COMPLICATED BY THE INCREASING MID AND HIGH CLOUDS AND THE LIGHT SOUTHERLY STIRRING AHEAD OF THE APPROACHING COLD FRONT. WILL FORECAST LOWS IN THE MID 40S WEST TO LOWER 40S EAST. HIGHS ON SUNDAY WILL BE COMPLICATED BY TE PRECIPITATION WHICH SHOULD KEEP HIGHS IN THE MID 50S ACROSS THE NORTHWEST PIEDMONT WITH MID 60S ACROSS THE SANDHILLS AND SOUTHERN COASTAL PLAIN WHERE THE RAIN WILL BE MORE SCATTERED. -BLAES
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&& .SHORT TERM /SUNDAY NIGHT/... AS OF 345 AM SATURDAY... WARM ADVECTION DRIVEN PRECIP...OUT AHEAD OF THE UPPER TROUGH AND COLD FRONT MOVING INTO THE OHIO/TENNESSEE VALLEYS SUNDAY MORNING... WILL BE PRIMARILY FOCUSED OVER THE NORTHWEST PIEDMONT. THIS INITIAL SURGE OF WARM ADVECTION IS FORECAST TO WEAKEN WITH TIME AND NORTHWARD EXTENT..WITH LIGHT QPF AMOUNTS OF A TENTH OF AN INCH OR LESS FOR MOST LOCATIONS. TO THE EAST...WHERE LIFT IS WEAKER AND MOISTURE IS LIMITED...ONLY A FEW HUNDREDTHS ARE EXPECTED. HAVE ADJUSTED POPS TO SHOW A GREATER RANGE FROM HIGH END LIKELY INT HE NORTHWEST TO LOW END CHANCE IN THE SOUTHEAST. BY SUNDAY AFTERNOON...TEMP ADVECTION BECOMES NEARLY NEUTRAL WITH NO SIGNS OF ANY APPRECIABLE WAVES IN THE DEEP SOUTHWESTERLY FLOW. THUS...EXPECT A LULL IN PRECIP THROUGH SUNDAY LATE AFTERNOON/EVENING...BEFORE THE COLD FRONT SINKS SOUTH INTO NC SUNDAY NIGHT AND MORE WIDESPREAD RAIN SPREADS BACK IN FROM THE SOUTHWEST BY MONDAY MORNING IN RESPONSE TO A 180KT UPPER JET OVER THE OHIO VALLEY AND STRENGTHENING ISENTROPIC LIFT. THE RESULTING HIGHS SUNDAY AFTERNOON WILL EXHIBIT A GREATER RANGE OF VALUES...WITH MID 50S IN THE NORTHWEST TO MID 60S POSSIBLE IN THE SOUTHEAST. LOWS SUNDAY NIGHT IN THE MID 40S NORTH TO LOWER 50S SOUTH. && .LONG TERM /MONDAY THROUGH FRIDAY/... AS OF 325 AM SATURDAY... MON AND MON NIGHT: THE MODELS ARE IN GOOD AGREEMENT ALOFT REGARDING THE AMPLIFICATION OF A SHORTWAVE TROUGH ACROSS NORTHERN MEXICO THROUGH TONIGHT... FOLLOWED BY A DEAMPLIFICATION OF THE TROUGH TO THE MIDDLE ATLANTIC STATES BY EARLY MON. THE INTENSIFICATION AND MIGRATION OF AN ASSOCIATED 160-180 KT UPPER JET ACROSS THE OH VALLEY AND NORTHEAST WILL PLACE CENTRAL NC BENEATH THE RIGHT ENTRANCE REGION OF THE JET...WHICH WILL CAUSE THE LOW LEVEL FLOW /ABOVE THE SHALLOW POST-FRONTAL DAMMING HIGH/ TO ACCELERATE AND ASSUME A MORE SOUTHERLY COMPONENT. STRENGTHENING ISENTROPIC LIFT WILL RESULT...WHICH WILL CAUSE LIGHT RAIN TO OVERSPREAD CENTRAL NC LATE SUNDAY NIGHT THROUGH EARLY MON AFTERNOON...BEFORE TAPERING TO OCCASIONAL DRIZZLE OR BARELY MEASURABLE LIGHT RAIN...AS AN ASSOCIATED SERIES OF WEAK FRONTAL WAVES TRACK OFF THE COAST OF THE CAROLINAS...THROUGH MON NIGHT. THE COMBINATION OF BOTH CAA AND DIABATIC/EVAPORATIVE COOLING WILL LIKELY RESULT IN SLOWLY FALLING TEMPERATURES ACROSS THE NORTHERN CWFA --INTO THE 40S-- THROUGHOUT THE DAY...WHILE THE SOUTHERN TIER WILL HAVE AN OPPORTUNITY TO WARM INTO THE 60S DURING THE MIDDAY HOURS BEFORE ALSO COOLING DURING THE AFTERNOON HOURS. LOWS...WITH CONTINUED LOW OVERCAST AND THE AFOREMENTIONED OCCASIONAL DRIZZLE OR VERY LIGHT RAIN...IN THE UPPER 30S TO LOWER 40S. TUE: A SECONDARY SHORTWAVE TROUGH...ANOTHER DEAMPLIFYING ONE IN WSW FLOW ALOFT...IS FORECAST TO CROSS THE CENTRAL APPALACHIANS EARLY TUE. THE PASSAGE OF THIS FEATURE AND ASSOCIATED WEAK HEIGHT FALLS ALOFT AND LIFT WILL MAINTAIN A SUFFICIENTLY SATURATED LOWEST SEVERAL THOUSAND FT TO WARRANT A CONTINUED SLIGHT CHANCE OF LIGHT RAIN OR (MORE LIKELY) DRIZZLE INTO EARLY TUE...BEFORE NW 925-850 MB FLOW BEHIND THE PASSING SHORTWAVE PROMOTES BOTH DOWNSLOPE FLOW AND A DISSIPATION OF THE CAD INVERSION VIA CAA - BOTH MECHANISMS THAT SHOULD SERVE TO SCOUR THE CAD REGIME AND PROMOTE STEADY CLEARING. WITH A FEW HOURS OF AFTERNOON SUNSHINE PROBABLE...LONGEST OVER THE NW PIEDMONT...TEMPERATURES SHOULD RESPOND TO NEAR NORMAL. TUE NIGHT-FRI: STRONG...ARCTIC HIGH PRESSURE OVER THE ROCKIES EARLY IN THE PERIOD WILL OTHERWISE SPRAWL EAST ACROSS THE MIDDLE ATLANTIC AND SOUTHEAST STATES...THROUGH THU...BENEATH GENERALLY WESTERLY FLOW BETWEEN CONFLUENT BRANCHES OF THE UPPER JET...BEFORE DRIFTING OFFSHORE AHEAD OF AN EJECTING DESERT SW (BRIEFLY) CUTOFF LOW FRI- SAT. THE RESULT WILL BE COOL CONDITIONS --MOST NOTABLY WED AND THU MORNINGS WHEN TEMPERATURES SHOULD DIP WELL INTO THE 20S GIVEN PROJECTED LOW LEVEL THICKNESS VALUES IN THE 1290-1300 METER RANGE-- WITH A PERIOD OF PASSING MID-HIGH CLOUDS DURING THE DAY WED...BETWEEN OTHERWISE MOSTLY CLEAR. MEDIUM RANGE GUIDANCE (NOT SURPRISINGLY) DIVERGES WITH RESPECT TO THE EJECTION OF THE AFOREMENTIONED DESERT SW LOW...SO FORECAST DETAILS ARE MORE UNCERTAIN FOR FRI...THOUGH CLOUDINESS AND RAIN CHANCES WILL CERTAINLY BE ON THE RISE THROUGH THE START OF NEXT WEEKEND. && .AVIATION /12Z SATURDAY THROUGH WEDNESDAY/... AS OF 1250 PM SATURDAY... ...HIGH CONFIDENCE OF VFR CONDITIONS THROUGH MIDNIGHT TONIGHT WITH ADVERSE AVIATION CONDITIONS SPREADING INTO MUCH OF CENTRAL NC EARLY SUNDAY... VFR CONDITIONS ARE EXPECTED ACROSS CENTRAL NC THIS AFTERNOON AND EVENING AS HIGH AND MID LEVEL CLOUDINESS INCREASES LATE. AN AREA OF SHOWERS ACROSS UPSTATE GA/SC WILL MOVE INTO WESTERN NC VERY LATE THIS AFTERNOON BUT THIS PRECIPITATION SHOULD LARGELY DISSIPATE. IF SOMEHOW IT MAKES IT INTO THE WESTERN PIEDMONT IT WOULD OCCUR AS A VFR RAIN SHOWER WITH A HIGH CEILING AND LIMITED VISIBILITY REDUCTION. MORE SIGNIFICANT WEATHER ARRIVES WELL AFTER MIDNIGHT AS DEEPER MOISTURE IS DRAWN INTO CENTRAL NC AHEAD OF AN APPROACHING COLD FRONT. RAIN WILL SPREAD INTO THE WESTERN PIEDMONT FROM THE SOUTHWEST BETWEEN 10-14Z INCLUDING THE KINT AND KGSO TERMINALS AND THEN MOVE EAST ARRIVING AROUND 13-17Z AT KRDU AND KRWI WITH SEVERAL HOURS OF RAIN EXPECTED IN THE TRIAD. SPOTTIER RAIN IS EXPECTED NEAR KFAY OCCURRING FROM 15-22Z. THE BEST SUPPORT FOR PRECIPITATION WILL OCCUR ACROSS NORTHWESTERN NC WITH THE AMOUNT...DURATION AND LIKELIHOOD OF PRECIPITATION DECREASING TOWARD THE SOUTHEAST. IN THE TRIAD CEILINGS SHOULD FALL INTO THE IFR TO POSSIBLY LIFR RANGE AFTER PRECIPITATION BEGINS WITH VSBYS IN THE MVR/IFR RANGE...CONDITIONS ESPECIALLY CIGS WILL LIKELY BE A LITTLE BETTER BUT STILL REDUCED TO THE EAST AT KRDU AND KRWI AND SHOULD BE BETTER FURTHER SOUTH AND EAST AT KFAY. LIGHT SOUTH-SOUTHWEST WINDS AT 190-250 DEG AT LESS THAN 10KTS WILL CONTINUE THROUGH THE 24 HOUR TAF PERIOD. LOOKING AHEAD...THE AREA OF PRECIPITATION ON SUNDAY SHOULD MOVE OUT OF THE AREA BY SUNSET BEFORE ANOTHER AREA OF RAIN ASSOCIATED WITH THE COLD FRONT AND A SURFACE WAVE MOVES ACROSS THE AREA LATE SUNDAY NIGHT AND MONDAY. LINGERING LOW CLOUDS AND DRIZZLE WILL CONTINUE MONDAY NIGHT INTO TUESDAY BEFORE CONDITIONS IMPROVE LATER TUESDAY WITH FAIR WEATHER EXPECTED ON WEDNESDAY. -BLAES && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...BLS NEAR TERM...BLAES SHORT TERM....BLS LONG TERM...MWS AVIATION...BLAES

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