Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 281219 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 715 AM EST SUN DEC 28 2014 .SYNOPSIS... A COLD FRONT WILL APPROACH FROM THE NORTHWEST TODAY... THEN PUSH SLOWLY SOUTHEAST THROUGH THE AREA MONDAY AND MONDAY NIGHT. HIGH PRESSURE WILL BUILD IN FROM THE WEST LATE TUESDAY THROUGH THURSDAY. && .NEAR TERM /THROUGH 6PM/... AS OF 350 AM SUNDAY... SOUTHWESTERLY FLOW CONTINUES ALOFT BETWEEN A DEEP LAYER RIDGE OVER THE CARIBBEAN AND A POSITIVELY TILTED UPPER TROUGH EXTEDNING FROM THE GREAT LAKES TO NORTHERN MEXICO. AN UPPER DISTURBANCE IN THE FLOW...ALONG WITH BROAD WARM ADVECTION OVER THE SOUTHEAST...IS FORCING AN AREA OF LIGHT TO MODERATE PRECIP ACROSS NORTHERN ALABAMA/GEORGIA. A FEW RADAR ECHOES ARE SHOWING UP OVER THE SOUTHERN AND WESTERN PIEDMONT...BUT PRECIP IS MOST LIKELY STILL EVAPORATING AS THE THE VERY DRY LAYER BELOW 5K FT (PER 00Z KGSO RAOB) CONTINUES TO MOISTEN. GIVEN THAT ISENTROPIC LIFT AND WARM ADVECTION ARE EXPECTED TO WANE WITH TIME AND NORTHERN EXTENT THIS MORNING...THE RAIN...WHILE STILL LIKELY AT MOST LOCATIONS...WILL BE VERY LIGHT WITH QPF OF ONLY A FEW HUNDREDTHS AND POTENTIALLY ONLY A TRACE FOR MANY. TEMPERATURES ARE CURRENTLY IN THE UPPER 40S TO LOWER 50S...AND ARENT LIKELY TO FALL MUCH MORE THIS MORNING. DEWPOINTS ARE IN THE UPPER 30S AND THERE WILL BE SOME EVAPORATIONAL COOLING...BUT GIVEN THE LIGHT QPF AND WARMER MORNING TEMPS...WILL RAISE FORECAST HIGHS A COUPLE DEGREES...56-66 NORTHWEST TO SOUTHEAST. && .SHORT TERM /TONIGHT THROUGH MONDAY NIGHT/...
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AS OF 345 AM SUNDAY... TONIGHT AND MONDAY... A COLD FRONT...WHICH IS CURRENTLY MOVING INTO THE OHIO VALLEY REGION...WILL PUSH SOUTHEAST INTO THE AREA BETWEEN 00Z AND 06Z. MEANWHILE...A SHORTWAVE WITHIN THE UPPER TROUGH WILL LIFT FROM TEXAS TOWARD THE SOUTHERN APPALACHIANS TONIGHT. WHILE DEAMPLIFYING...THIS SHORTWAVE COMBINED WITH THE RIGHT ENTRANCE REGION OF A 150KT UPPER JET OVER THE NORTHEAST US WILL BRING ANOTHER ROUND OF WIDESPREAD PRECIP LATE TONIGHT AND INTO MONDAY. THE RAIN IS EXPECTED TO SPREAD FROM WEST TO EAST AFTER MIDNIGHT TONIGHT AS A WEAK WAVE OF LOW PRESSURE MOVES ALONG THE FRONT AS IT NEARS THE NC/SC BORDER. WITH BETTER FORCING/MOISTURE THROUGH A DEEPER LAYER... RAINFALL AMOUNTS SHOULD BE HIGHER WITH THIS ROUND OF PRECIP...AS THE GFS AND ECMWF BOTH SHOULD UPWARDS OF A QUARTER OF AN INCH. HIGHS OF UPPER 40S NORTH TO LOW/MID 50S SOUTH ARE LIKELY TO OCCUR EARLY IN THE MORNING THEN FALL DURING THE AFTERNOON...ESPECIALLY ACROSS THE NORTH AS PRECIP OVERSPREADS THE POST-FRONTAL AIRMASS AND A WEAK COLD AIR DAMMING AIRMASS DEVELOPS. MONDAY NIGHT...COLD/DRY ADVECTION WILL CONTINUE BEHIND THE FRONT ...THOUGH THE COLD AIR DAMMING AIRMASS WILL BE MAINTAINED BY SOME SHALLOW UPGLIDE AND POCKETS OF LIGHT RAIN OF DRIZZLE. ALL MODELS KEEP THERMAL PROFILES ABOVE FREEZING THROUGH TUESDAY MORNING AND SUGGEST NO TYPE ISSUES. LOWS IN THE UPPER 30S AND LOWER 40S.
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&& .LONG TERM /TUESDAY THROUGH SATURDAY/... AS OF 340 AM SUNDAY... TUE: A WELL-DEFINED SHORTWAVE TROUGH OVER WA THIS MORNING WILL AMPLIFY ACROSS THE ROCKIES THROUGH TONIGHT...THEN DEAMPLIFY FROM THE CENTRAL PLAINS TO THE MIDDLE ATLANTIC COAST TUE THROUGH TUE NIGHT. THE PASSAGE OF THIS FEATURE AND ASSOCIATED GLANCING BLOW OF THE SOUTHERN PERIPHERY OF HEIGHT FALLS ALOFT...AND ASSOCIATED FORCING FOR ASCENT...WILL PRODUCED RENEWED LIFT ATOP A STILL-SATURATED LAYER IN ROUGHLY THE LOWEST SEVERAL THOUSAND FT --DEEPEST NEAR THE VA BORDER/IN CLOSEST PROXIMITY TO THE STRONGEST HEIGHT FALLS ALOFT OVER THE MIDDLE ATLANTIC-- SUCH THAT OTHERWISE PERIODS OF DRIZZLE THROUGH EARLY TUE WILL BECOME LIGHT RAIN DURING THE MORNING TO MIDDAY HOURS. BEHIND THE PASSING SHORTWAVE TROUGH...NW 925-850 MB FLOW WILL PROMOTE BOTH DOWNSLOPE FLOW AND A DISSIPATION OF THE CAD INVERSION VIA CAA - BOTH MECHANISMS THAT SHOULD SERVE TO SCOUR THE CAD REGIME AND PROMOTE CLEARING BY THE AFTERNOON OR EVENING. THE TIMING OF THIS PROCESS REMAINS IN QUESTION OWING TO TIMING DIFFERENCES AMONGST NWP GUIDANCE REGARDING THE PASSAGE OF THE SHORTWAVE TROUGH...THOUGH THERE HAS BEEN AN OVERALL SLOWER TREND EVIDENT IN THE GUIDANCE. AS SUCH...WILL FAVOR A SLOWER CLEARING TREND FROM WEST TO EAST SUCH THAT TEMPERATURES LIKELY WILL NOT HAVE TIME TO RESPOND TO THE SETTING AFTERNOON SUN...WHICH WOULD RESULT IN HIGHS ONLY IN THE LOWER TO MIDDLE 40S. IF A FEW HOUR PERIOD OF SUN DOES MATERIALIZE... MOST LIKELY OVER THE SOUTHERN AND WESTERN PIEDMONT DURING THE AFTERNOON...TEMPERATURES WOULD RESPOND TO NEAR NORMAL VALUES IN THE UPPER 40S. TUE NIGHT-SAT: 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 (WITH UPPER TEENS POSSIBLE IN OUTLYING AREAS THAT EXPERIENCE CALM) GIVEN PROJECTED LOW LEVEL THICKNESS VALUES IN THE 1290-1300 METER RANGE. IT WILL ALSO BE CLEAR OR MOSTLY SO DURING MOST OF THE PERIOD...WITH THE EXCEPTION OF A PERIOD OF PASSING MID-HIGH CLOUDS IN ASSOCIATION WITH A STRONGLY-SHEARED AND POSITIVELY-TILTED TRAILING SHORTWAVE TROUGH DURING THE DAY WED. WHILE MEDIUM RANGE GUIDANCE DIVERGES WITH RESPECT TO THE EJECTION OF THE AFOREMENTIONED DESERT SW LOW AND ASSOCIATED APPROACH OF THE NEXT FRONTAL SYSTEM...THE OVERALL PATTERN (WITH TIMING DIFFERENCES TO BE WORKED OUT) WOULD RESULT IN A LOW TRACK TO THE NW OF CENTRAL NC AND AN ASSOCIATED WARM FRONTAL PASSAGE IN RETURN FLOW AROUND THE DEPARTING AND MODIFIED ARCTIC HIGH --TIMING MOST LIKELY FRI NIGHT- SAT FAVORED (DUE TO TYPICAL FAST BIAS IN NWP WITH SW CUTOFFS) AS DEPICTED BY THE SLOWER EC AND EC MEAN. IF SHOWERS OCCUR WITH THE PASSAGE OF THE WARM FRONT...MOST LIKELY OVER THE WESTERN PIEDMONT... AN IN-SITU DAMMING EVENT WOULD EVOLVE INTO THE EARLY PART OF THE WEEKEND...IN A PATTERN OTHERWISE SUPPORTIVE OF WARMING TEMPERATURES OVER THE SE CONUS. AS SUCH...TEMPERATURES ON SAT ARE APT TO DISPLAY A WIDER THAN AVG RANGE OVER CENTRAL NC...WITH MARKEDLY COOLER TEMPERATURES OVER THE NW PIEDMONT. && .AVIATION /12Z SUNDAY THROUGH WEDNESDAY/...
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AS OF 715 AM SUNDAY... SO FAR THIS MORNING...THE WIDESPREAD RAIN APPROACHING NC FROM THE SOUTHWEST HAS BEEN VERY SLOW TO MAKE IT NORTH OF THE NC/SC BORDER...LIKELY OWING TO A VERY DRY LOW-LEVEL AIRMASS OVER NC. IN THE 12-15Z TIME FRAME...THE POTENTIAL FOR MVFR CEILINGS WILL BE GREATEST ACROSS THE SOUTHERN PIEDMONT AND SANDHILLS...INCLUDING THE KFAY TERMINAL. PRECIP SHOULD EVENTUALLY SPREAD FURTHER NORTH AND HAVE MORE IMPACT ON MORE TERMINALS ACROSS CENTRAL NC...WITH MVFR AND/OR IFR CEILINGS POSSIBLE...AT LEAST TEMPORARILY...BY THIS AFTERNOON. CONFIDENCE IS HIGHEST IN MVFR CONDITIONS AT KGSO AND KINT. EXPECT THE LIGHT RAIN TO THEN BE INTERMITTENT LATER THIS AFTERNOON AS A LULL DEVELOPS...WITH A PERIOD OF VFR CONDITIONS POSSIBLE BEFORE A COLD FRONT PUSHES INTO THE AREA FROM THE NORTH TONIGHT BETWEEN ROUGHLY 00Z AND 06Z. MEANWHILE...ANOTHER UPPER LEVEL DISTURBANCE WILL CROSS THE AREA...CAUSING SOUTHERLY FLOW TO INCREASE AND ANOTHER ROUND OF WIDESPREAD RAIN AND SUB-VFR CONDITIONS TO DEVELOP AFTER MIDNIGHT. WINDS WILL BE 5-10KT OUT OF THE SOUTHWEST TODAY...TURNING TO NORTHWESTERLY AND THEN NORTHERLY BEHIND THE FRONT TONIGHT. LOOKING AHEAD: LOW CEILINGS...ALONG WITH SOME PERIODS OF LIGHT RAIN OR DRIZZLE WILL LINGER THROUGH MONDAY NIGHT...WITH CONDITIONS EXPECTED TO IMPROVE LATE TUESDAY AND CONTINUE THROUGH MIDWEEK.
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&& .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...BLS NEAR TERM...BLS SHORT TERM....BLS LONG TERM...MWS AVIATION...BLS

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