Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 270852 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 345 AM 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 /THROUGH TONIGHT/...
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AS OF 345 AM SATURDAY.. HIGH PRESSURE OVER THE EASTERN HALF OF NC THIS MORNING WILL CONTINUE TO SHIFT OFFSHORE TODAY...WHILE A POSITIVELY TILTED UPPER TROUGH AND ASSOCIATED FRONTAL ZONE BEGIN TO SLOWLY MAKE THEIR TRANSITION EAST ACROSS THE CENTRAL US. A FEW AREAS OF HIGH CLOUDS CONTINUE TO DRIFT ACROSS THE NORTHERN PORTIONS OF THE AREA...WITH MORE ROBUST CLOUD COVER STILL WELL WEST OF THE TENNESSEE VALLEY REGION. DESPITE SHALLOW MIXING...THICKNESSES STARTING OUT NEAR 1340M SUGGESTS HIGHS WILL BE 2-4 DEGREES WARNER THAN FRIDAY IN MANY AREAS....61-65. AHEAD OF THE AFOREMENTIONED UPPER TROUGH...A SURGE OF WARM ADVECTION WILL SPREAD PRECIP FROM THE DEEP SOUTH ACROSS THE SOUTHERN APPALACHIANS TONIGHT. WHILE MID/HIGH LEVEL MOISTURE WILL SPREAD IN QUICKLY AFTER SUNSET...FORECAST SOUNDINGS SHOW THE LOWEST 7K FT REMAINING RATHER DRY. MODELS ARE OFTEN TOO SLOW WITH THE ARRIVAL OF PRECIP FROM THE SOUTHWEST...BUT IT WILL TAKE SOME TIME TO MOISTEN THE LOW-LEVELS....AND PRECIP MAY NOT REACH THE GROUND UNTIL AFTER 09Z. TEMPS WILL FALL MORE QUICKLY EARLY IN THE NIGHT...ESPECIALLY IN THE EAST...BUT CLOUDS THICKEN AFTER MIDNIGHT. EXPECT LOWS IN THE MID 40S WEST TO LOWER 40S AND SOME UPPER 30S IN THE EAST.
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&& .SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/...
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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.
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&& .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 /06Z SATURDAY THROUGH TUESDAY/... AS OF 100 AM SATURDAY... WITH DEWPOINTS SLIGHTLY HIGHER OVER THE COASTAL PLAIN AND LIGHT WINDS...THERE MAY BE A COUPLE HOURS OF MVFR VSBY AT KRWI AND/OR KFAY PRIOR TO 12Z...ESPECIALLY AS SKIES PARTIALLY CLEAR BETWEEN SOME HIGH CLOUDS MOVING OVERHEAD. OTHERWISE.. VFR CONDITIONS ARE EXPECTED TO CONTINUE THROUGH THE TAF PERIOD WITH LIGHT WINDS BECOMING SOUTH- SOUTHWESTERLY DURING THE DAY. MID-LEVEL CLOUDS WILL INCREASE LATER TONIGHT AND EARLY SUNDAY AHEAD OF A DISTURBANCE MOVING ALONG THE APPALACHIANS. HOWEVER...CURRENT MODEL PROJECTIONS HAVE LOW CLOUDS AND SUB-VFR CEILINGS SPREADING INTO THE KGSO/KINT VICINITY WELL AFTER 06Z SUNDAY. LOOKING AHEAD: A SERIES OF UPPER-LEVEL DISTURBANCES MOVING SOUTHWEST TO NORTHEAST ACROSS THE REGION COMBINED WITH AN APPROACHING FRONTAL ZONE WILL BRING A COUPLE ROUNDS OF LIGHT PRECIP AND SUB-VFR CONDITIONS TO PORTIONS OF CENTRAL NC SUNDAY AND MONDAY. CONDITIONS ARE EXPECTED TO IMPROVE BY LATE MONDAY NIGHT INTO TUESDAY. -KRD && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...BLS NEAR TERM...BLS SHORT TERM....BLS LONG TERM...MWS AVIATION...BLS

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