AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 548 AM EST THU DEC 25 2014 .SYNOPSIS...A COLD FRONT WILL SWEEP EASTWARD THROUGH THE REGION THIS MORNING. HIGH PRESSURE WILL BUILD INTO THE CAROLINAS FROM THE SOUTHWEST TONIGHT AND PERSIST THROUGH FRIDAY BEFORE SHIFTING OFFSHORE FRIDAY NIGHT INTO SATURDAY. && .NEAR TERM /TODAY TONIGHT/... AS OF 545 AM THURSDAY... OVERVIEW: A POSITIVELY TILTED /INCREASINGLY SHEARED/ UPPER LEVEL TROUGH CENTERED ALONG THE APPALACHIANS AT 07Z WILL PROGRESS EASTWARD THROUGH THE CAROLINAS THIS AFTERNOON AND OFFSHORE THIS EVENING. AN ASSOCIATED COLD FRONT (CROSSING THE I-77 CORRIDOR AT 07Z) WILL PROGRESS EASTWARD THROUGH CENTRAL NC THIS MORNING. IN THE WAKE OF THE FRONT...SFC HIGH PRESSURE WILL BUILD INTO THE CAROLINAS FROM THE SOUTHWEST LATE THIS AFTERNOON INTO TONIGHT IN ASSOC/W H5 HEIGHT RISES OVER THE SOUTHEASTERN US. 530 AM UPDATE: THE LATEST OBSERVATIONAL DATA INDICATES PRIOR FORECAST REASONING IS IN ERROR. THE SYNOPTIC COLD FRONT (APPROACHING HWY 1 AT 10Z) HAS ACCELERATED THE RESIDUAL WEDGE AIRMASS EASTWARD THROUGH THE COASTAL PLAIN...WIPING OUT THE REMAINING WARM SECTOR. AS A RESULT...THE THERMODYNAMIC ENVIRONMENT IN CENTRAL NC IS NO LONGER SUPPORTIVE OF ADDITIONAL SHOWER DEVELOPMENT ALONG THE SYNOPTIC COLD FRONT...AND PRECIP CHANCES HAVE BEEN REMOVED. -VINCENT PRIOR REASONING THROUGH 12Z: SCATTERED SHOWER ACTIVITY IN ADVANCE OF THE APPROACHING COLD FRONT (STILL LOCATED WEST OF THE YADKIN AT 07Z) NEAR THE HWY 1 CORRIDOR IS DEVELOPING ALONG A BAROCLINIC ZONE MARKING THE INTERFACE BETWEEN THE RESIDUAL WEDGE AIRMASS OVER THE WESTERN PIEDMONT AND THE PRE-FRONTAL WARM SECTOR OVER THE COASTAL PLAIN...APPARENTLY IN ASSOC/W SHALLOW LOW-LEVEL CONVERGENCE AND DPVA ATTENDANT SMALL AMPLITUDE WAVES IN SW FLOW ALOFT IN THE PRESENCE OF WEAK WARM SECTOR INSTABILITY. EXPECT THE AFOREMENTIONED ACTIVITY TO EVOLVE INTO A MORE DISTINCT NNE-SSW ORIENTED LINE OF SHOWERS ALONG THE HWY 1 CORRIDOR BETWEEN 08-10Z AS LOW-LEVEL CONVERGENCE INCREASES AND STRONGER DPVA ARRIVES FROM THE WEST AS THE SYNOPTIC COLD FRONT OVERTAKES (OR MERGES INTO) THE RESIDUAL CAD WEDGE. REGARDLESS... SHOWER ACTIVITY WILL EXIT THE COASTAL PLAIN WITH THE FRONT ~12Z. TODAY AND TONIGHT: EXPECT CLEARING BY AFTERNOON AS SYNOPTIC SUBSIDENCE /HEIGHT RISES/ COMMENCE IN THE WAKE OF THE SHEARED UPPER LEVEL TROUGH AND SFC COLD FRONTAL PASSAGE...WITH HIGHS RANGING FROM LOWER 50S NW TO UPPER 50S SE. WITH CLEAR SKIES...CALM WINDS AND A DRY AIRMASS IN PLACE ONCE AGAIN...EXPECT EXCELLENT RADIATIONAL COOLING WITH LOWS IN THE UPPER 20S (TYPICAL RURAL AND LOW-LYING ARAS) TO LOWER 30S ELSEWHERE. -VINCENT && .SHORT TERM /FRIDAY AND FRIDAY NIGHT/... AS OF 345 AM THURSDAY... CLEAR SKIES AND DRY CONDITIONS WILL PREVAIL AS HEIGHTS CONTINUE TO RISE IN ASSOC/W SFC HIGH PRESSURE CENTERED OVER THE CAROLINAS AND AN AMPLIFYING UPPER LEVEL RIDGE OVER THE SOUTHEASTERN CONUS. HIGHS SIMILAR ALBEIT SLIGHTLY WARMER THAN TODAY...IN THE MID/UPPER 50S TO LOWER 60S. LOWS FRI NIGHT SIMILAR TO TONIGHT... IN THE UPPER 20S TO LOWER 30S. -VINCENT && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... AS OF 230 AM THURSDAY... SATURDAY AND SATURDAY NIGHT: HIGH PRESSURE CENTERED OVER COASTAL NC AT 12Z SATURDAY WILL SHIFT OFFSHORE AS A COLD FRONT CROSSING THE MIDWEST MOVES TOWARD THE OHIO VALLEY. LOOK FOR CLOUDS TO GRADUALLY INCREASE AND THICKEN THROUGH THE DAY AS SW FLOW AHEAD OF THE FRONT INCREASES. OTHERWISE WE SHOULD SEE FAIR-WEATHER WITH TEMPS STILL 10+ DEG ABOVE NORMAL...HIGHS AROUND 60 AND LOWS IN THE LOWER-MID 40S. SUNDAY AND SUNDAY NIGHT: THE CHANCE FOR RAIN WILL RETURN AS THE AFOREMENTIONED COLD FRONT DROPS SOUTH AND STALLS ACROSS THE CAROLINAS...WHILE WAVES OF ENERGY AND MOISTURE IN THE SW FLOW ALOFT MOVE ACROSS THE REGION. DAYTIME HIGHS WILL BE A FEW DEG COOLER GIVEN THE CLOUDS AND RAIN...BUT LITTLE CHANGE FOR NIGHT-TIME LOWS. EARLY NEXT WEEK...MONDAY THROUGH TUESDAY: UNSETTLED AND POTENTIALLY DAMP WEATHER WILL CONTINUE AS THE AFOREMENTIONED BOUNDARY DRIFTS TO OUR SOUTH AND MOIST SW FLOW ALOFT OVERRUNS THE COOL NE LOW LEVEL FLOW NORTH OF THE BOUNDARY. THE AIRMASS WILL GRADUALLY COOL DURING THIS TIME AS THE SFC BOUNDARY DRIFTS SOUTH...ALLOWING THE COOLER AIRMASS TO SETTLE INTO THE REGION FROM THE NORTH. MIDWEEK AND BEYOND: A BRIEF BREAK IN THE DAMP WEATHER MAY COME ON WEDNESDAY AS HIGH PRESSURE AND SLIGHTLY DRIER AIR SETTLES OVER THE REGION. THIS MAY BE SHORT-LIVED THOUGH...AS ENERGY EJECTING NORTHEASTWARD FROM THE TROUGH OVER THE SW STATES...AND MOISTURE LIFTING NORTH FROM THE GULF COAST REGION...APPROACH THE CAROLINAS FOR THE LATE-WEEK PERIOD. && .AVIATION /12Z THURSDAY THROUGH SUNDAY/... AS OF 545 AM THURSDAY... 24-HR TAF PERIOD: VFR CONDITIONS WILL RULE THROUGH THE TAF PERIOD AS A DRIER AIRMASS ADVECTS INTO THE REGION FROM THE WEST IN THE WAKE OF A RECENT COLD FRONTAL PASSAGE. WINDS WILL BECOME WESTERLY/WSW AT 10- 15 KT WITH OCCASIONAL GUSTS UP TO 20 KT THIS MORNING...EVENTUALLY DECREASING TO ~10 KT DURING THE AFTERNOON...THEN BECOMING CALM AFTER SUNSET AS HIGH PRESSURE BUILDS OVERHEAD. LOOKING AHEAD: HIGH PRESSURE WILL LINGER DIRECTLY OVER CENTRAL NC ON FRIDAY...PROGRESSING OFFSHORE (THOUGH STILL EXTENDING WESTWARD INTO THE AREA) FRIDAY NIGHT AND SATURDAY. AS A RESULT...VFR CONDITIONS /MOSTLY CLEAR SKIES/ AND LIGHT WINDS WILL PREVAIL THROUGH SAT. MVFR/IFR CEILINGS AND A CHANCE FOR RAIN CAN BE EXPECTED SATURDAY NIGHT THROUGH SUNDAY NIGHT AS AN APPROACHING COLD FRONT TEMPORARILY STALLS OVER THE SOUTHEASTERN CONUS. -VINCENT && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. &&
Posted on: Thu, 25 Dec 2014 13:17:34 +0000
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