AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
325 AM EST SUN DEC 21 2014

.SYNOPSIS...WEAK LOW PRESSURE WILL MOVE OFF THE SOUTHEAST COAST 
TONIGHT...AS HIGH PRESSURE REMAINS OVER THE AREA THROUGH SUNDAY. 
ANOTHER LOW PRESSURE SYSTEM WILL MOVE ALONG THE CAROLINA COAST 
MONDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 325 AM SUNDAY...

TODAY...SURFACE HIGH CENTERED OVER THE EASTERN GREAT LAKES EARLY 
THIS MORNING WILL DRIFT EAST ACROSS THE NORTHERN MID ATLANTIC 
TODAY...AND EXTEND SWD INTO THE CAROLINAS. ALOFT A WEAK...RELATIVELY 
FLAT...S/W RIDGE WILL CROSS OUR AREA. THE COMBINED EFFECTS OF THESE 
TWO FEATURES SHOULD MAINTAIN DRY CONDITIONS UNTIL LATE AFTERNOON. 
ABUNDANT MOISTURE IN THE LOWER LEVELS OF THE ATMOSPHERE WILL RESULT 
IN WIDESPREAD CLOUDINESS OVER MOST OF THE PIEDMONT AND SANDHILLS 
EARLY THIS MORNING. IN THE COASTAL PLAIN WHERE PARTIAL CLEARING HAS 
OCCURRED...EXPECT LOW CLOUDS AND/OR FOG TO DEVELOP PRIOR TO 
DAYBREAK. EXPECT PARTIAL CLEARING ACROSS MOST OF CENTRAL NC LATER 
THIS MORNING IN RESPONSE TO WEAK SUBSIDENCE MIXING DRIER AIR ALOFT 
TOWARDS THE SURFACE. MAX TEMPS THIS AFTERNOON DEPENDENT ON THIS 
PARTIAL CLEARING TO ALLOW FOR BITS OF SUN...WARMING TEMPS WELL INTO 
THE 40S WITH LOWER 50S POSSIBLE ACROSS THE SOUTH. IF PARTIAL 
CLEARING FAILS TO MATERIALIZE...THEN MAX TEMPS WILL MOSTLY LIKELY BE 
IN THE MID-UPPER 40S.

LATE THIS AFTERNOON-TONIGHT...MODEL GUIDANCE IN GOOD AGREEMENT IN 
ITS DEPICTION OF A SOUTHERN STREAM S/W PROJECTED TO CROSS THE LOWER 
MS VALLEY AND INDUCE WEAK SFC WAVE DEVELOPMENT OFF THE SC COAST BY 
EARLY MONDAY. WHILE THE DRY AIR SFC RIDGE WILL MAINTAIN A PRESENCE 
OVER CENTRAL NC...DEVELOPING SLY FLOW A FEW THOUSAND FEET ALOFT WILL 
INITIATE AN OVERRUNNING EVENT...LEADING TO A CLASSICAL OR HYBRID 
COLD AIR DAMMING EVENT. AS SLY FLOW STRENGTHENS OVERNIGHT...EXPECT 
RAIN TO OVERSPREAD THE REGION FROM THE SOUTH...LOCKING IN THE CAD 
AIR MASS. SPOTS OF LIGHT PRECIP MAY BREAK OUT PRIOR TO SUNSET ACROSS 
THE FAR SOUTH BUT BEST LIFT EXPECTED TO OCCUR AFTER MID-LATE EVENING 
IN THE SOUTH...AND AFTER MIDNIGHT ACROSS THE NORTH. PLAN TO ADJUST 
POPS IN THIS DIRECTION...WITH LIKELY POPS ACROSS THE FAR SOUTH BY 
01Z-02Z WITH SLIGHT CHANCE ACROSS THE NORTH...BECOMING CATEGORICAL 
BY EARLY MONDAY ACROSS THE SOUTH AND LIKELY ACROSS THE NORTH. MODEL 
PRECIP AMOUNTS NOT AS ROBUST AS 24-36 HOURS AGO WITH AMOUNTS THROUGH 
SUNDAY NIGHT-EARLY MONDAY ABOUT A TENTH OF A INCH OR LESS. 
INCREASING/THICKENING CLOUDS OVERNIGHT WILL AID TO MODERATE TEMPS SO 
EXPECT MIN TEMPS TO OCCUR AROUND OR SHORTLY AFTER MIDNIGHT WITH 
STEADY TEMPS THEREAFTER. MIN TEMPS 35-40. 

&&

.SHORT TERM /MONDAY AND MONDAY NIGHT/...
AS OF 325 AM SUNDAY...

MONDAY...BEST LIFT ASSOCIATED WITH THE SOUTHERN STREAM S/W WILL 
AFFECT OUR REGION MONDAY MORNING THEN LIFT NEWD OUT OF OUR AREA 
MONDAY AFTERNOON. THUS...WILL ADVERTISE HIGHEST POPS IN THE MORNING 
WITH DECREASING POPS IN THE AFTERNOON. AGAIN MODEL CONSENSUS HAS 
DECREASED EXPECTED RAINFALL AMOUNTS COMPARED TO 24 HOURS AGO BUT 
STILL EXPECT AROUND A QUARTER OF AN INCH. THE WIDESPREAD RAIN EARLY 
IN THE DAY WILL AID TO LOCK IN THE CAD AIR MASS AND ASSOCIATED LOW 
CLOUDS. THIS WILL RESULT IN MAX TEMPS JUST 5-8 DEGREES WARMER THAN 
EXPECTED MIN TEMPS. MAX TEMPS NEAR 40 NW TO NEAR 50 FAR SE. 

MONDAY NIGHT...CAD AIR MASS EXPECTED TO PERSIST MAINTAINING 
EXTENSIVE CLOUDINESS WITH AREAS OF DRIZZLE OR SPOTTY LIGHT RAIN. 
TEMPS USUALLY DO NOT DISPLAY MUCH DIURNAL CHANGE IN THIS TYPE OF AIR 
MASS SO MIN TEMPS EXPECTED TO RANGE FROM THE MID 30S NW TO THE LOW-
MID 40S SE. 

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
AS OF 215 AM SUNDAY... 

...WARM... WET AND RATHER WINDY SYSTEM TO AFFECT OUR REGION TUESDAY 
NIGHT THROUGH CHRISTMAS EVE... THEN WINDY AND COOLER CHRISTMAS DAY...

THERE IS HIGH CONFIDENCE OF A WARM... WET AND WINDY SYSTEM WILL 
AFFECT OUR REGION MID WEEK. MODELS AND ENSEMBLES AGREE IN GENERAL IN 
THAT A THE MAIN SURFACE STORM TRACK WILL BE FROM THE GULF OF MEXICO 
NORTHWARD THROUGH THE TENNESSEE AND OHIO VALLEY REGIONS TUE NIGHT 
INTO WEDNESDAY NIGHT. THE OPERATIONAL GFS IS SLOWER/A BIT WEAKER 
WITH THE MAIN SURFACE WAVE... DEPICTING A 997 MB SURFACE LOW OVER KY 
18Z/WED... WHILE THE AVERAGE OF THE ENSEMBLES SUGGEST AROUND A 992 
LOW OVER OR NEAR NW OHIO 12Z/WED. REGARDLESS... WITH THE STORM 
HEADING UP THE WEST SIDE OF THE APPALACHIANS... OUR REGION WILL HAVE 
TO DEAL WITH RESIDUAL COLD AIR DAMMING... A RETREATING 
WEDGE/WARM/COASTAL FRONT... AND THEN THE MAIN COLD FRONT. TIMING OF 
THESE WILL BE CRITICAL TO THE SENSIBLE WEATHER FORECASTS. THIS FAR 
OUT... THESE DETAILS WILL HAVE TO BE REFINED AS THE EVENT EVOLVES. 
AT THIS POINT WE WILL MAINTAIN CONTINUITY FROM OUR PREVIOUS 
FORECASTS AND BLEND IN THE LATEST ENSEMBLE MEANS TO GIVE IT OUR BEST 
SHOT AT EACH OF THESE FEATURES. ONE THING FOR SURE... CONFIDENCE IS 
100 PERCENT IN ALL RAIN. 

TUESDAY AND TUESDAY NIGHT... LINGERING COLD AIR DAMMING IS EXPECTED 
TO BE IN PLACE OVER A GOOD PORTION OF THE PIEDMONT DAMMING REGION 
12Z/TUESDAY. AN INITIAL WEAK SURFACE WAVE SHOULD BE TRACKING OFF THE 
DELMARVA COAST WITH A TRAILING COASTAL FRONT INTO SE GEORGIA. THIS 
COASTAL FRONT APPEARS THAT IT WILL HAVE A DIFFICULT TIME COMING 
INLAND INITIALLY GIVEN THAT THE MAIN STORM TRACK AND DYNAMICS WILL 
BE LIFTING NORTH (WEST OF THE MOUNTAINS) INSTEAD OF COMING EAST OR 
NORTHEAST ACROSS THE MOUNTAINS. THE PRESSURE GRADIENT WILL BE 
LACKING TUESDAY. HOWEVER... THE WAA PATTERN WILL INCREASE LATER 
TUESDAY INTO TUESDAY NIGHT AS THE SURFACE WAVE STRENGTHENS OVER THE 
TENNESSEE VALLEY AND LIFTS TOWARD OHIO BY 12Z/WED. WAA RAINS WILL BE 
AIDED BY WARM FRONTAL LIFT FROM THE SOUTHEAST LATE TUESDAY NIGHT 
INTO EARLY WEDNESDAY. SOME OF THE LATEST GUIDANCE SUGGESTS THE 
HEAVIEST RAINS MAY FALL OVER THE WESTERN PIEDMONT INTO THE MOUNTAINS 
ALONG AND NEAR THE RETREATING WARM/COASTAL FRONT. IT IS STILL 
DIFFICULT TO FORECAST EXACTLY WHERE THE WARM FRONT WILL BE LOCATED 
12Z/WED... BUT WHEN CLIMATOLOGY IS APPLIED TO THE GIVEN STORM TRACK 
AND STRENGTH ALONG WITH THE LINGERING CAD (RETREATING SURFACE HIGH 
OF 1030 MB OFF NEW ENGLAND)... THE WARM FRONT MOST LIKELY WILL BE 
VERY NEAR THE SE PIEDMONT FROM CHARLOTTE TO RALEIGH EARLY IN THE DAY 
WED. THE FRONT SHOULD LIFT INTO VIRGINIA DURING THE AFTERNOON. THIS 
WILL LIKELY LEAD TO A LULL IN THE WARM FRONTAL RAINS AS THEY LIFT 
INTO VIRGINIA WEDNESDAY AFTERNOON. 

THE MAIN COLD FRONT SHOULD ARRIVE BETWEEN 00Z/06Z THURSDAY 
(WEDNESDAY NIGHT)... ACCOMPANIED BY ADDITIONAL SHOWERS AND POSSIBLY 
A FEW THUNDERSTORMS (IF THE LOW LEVELS CAN DESTABILIZE ENOUGH WHICH 
IS IN DOUBT - GIVEN THE TIME OF YEAR. HOWEVER... SURFACE DEW POINTS 
WEDNESDAY AFTERNOON IN THE WARM SECTOR SHOULD REACH 60 OR EVEN 65 
SE. BREEZY TO WINDY SW FLOW AT 10-25 MPH CAN BE EXPECTED WITH TEMPS 
INTO THE 65-72 RANGE. THIS WOULD STILL ONLY YIELD MUCAPES OF 100 TO 
200 J/KG. IN ADDITION... THE STRONGEST LOW LEVEL JET IS EXPECTED TO 
PUSH NORTHWARD INTO VA/MD BY EARLY WEDNESDAY AFTERNOON ALONG THE 
RETREATING WARM FRONT. WITH THE MAIN DYNAMICS PASSING OVER THE GREAT 
LAKES... THESE FACTORS WILL GREATLY LIMIT ANY SEVERE POTENTIAL WITH 
THIS STORM FOR CENTRAL NC. 
  
SENSIBLE WEATHER TUESDAY THROUGH WEDNESDAY... 

COOL AND CLOUDY TUESDAY WITH SOME LIGHT DRIZZLE. THEN A CHANCE OF 
RAIN AGAIN IN TEH AFTERNOON IN THE SW. HIGHS IN THE MID 40S TO MID 
50S (PROBABLY NOT UNTIL TUESDAY EVENING). PERIODS OF RAIN... SOME 
HEAVY TUESDAY NIGHT INTO WEDNESDAY MORNING. RAIN ENDING FROM THE 
SOUTH BY AFTERNOON. THEN SHOWERS AND A SLIGHT CHANCE OF 
THUNDERSTORMS AGAIN IN THE MID TO LATE AFTERNOON (NW)... LATE 
AFTERNOON AND EVENING ELSEWHERE.  BECOMING WINDY AND WARMER FROM THE 
SOUTH TUESDAY NIGHT INTO WEDNESDAY (NW ZONES LATEST TO SEE WARMING). 
TEMPS RISING LATE WITH READINGS MID 50S TO MID 60S BY 12Z/WED NW TO 
SE. HIGHS WEDNESDAY IN THE MID 60S TO LOWER 70S. SHOWERS TAPER OFF 
QUICKLY FROM THE WEST WEDNESDAY NIGHT. CLOUDY WITH LOWS IN THE 40S 
TO LOWER 50S. 

THURSDAY THROUGH SATURDAY... THE PRESSURE GRADIENT WILL REMAIN TIGHT 
THURSDAY WITH A GUSTY W-NW WIND AT 15-25 MPH. HIGHS GENERALLY IN THE 
50S WITH PARTLY TO MOSTLY SUNNY SKIES. FRIDAY SHOULD BE DRY WITH 
ANOTHER COLD FRONT EXPECTED TO AFFECT THE REGION BY LATE FRIDAY 
NIGHT AND SATURDAY WITH A CHANCE OF RAIN SHOWERS. LOWS 35-40. HIGHS 
55-62.

&&

.AVIATION /06Z SUNDAY THROUGH THURSDAY/...
AS OF 105 AM SUNDAY...

WIDESPREAD MVFR/LOW END VFR CEILINGS WILL PERSIST THROUGH DAYBREAK 
ACROSS MUCH OF THE PIEDMONT. OVER THE COASTAL PLAIN AND THE 
SANDHILLS INCLUDING THE KFAY AND KRWI TERMINALS...PARTIAL CLEARING 
WILL ALLOW AREAS OF FOG AND LOW CLOUDS TO DEVELOP. THIS MAY LEAD TO 
AREAS OF MVFR/IFR CONDITIONS BETWEEN 08Z-12Z.

AFTER 12Z...IMPROVING CONDITIONS ANTICIPATED AS DRIER AIR ALOFT 
SHOULD MIX DOWN TOWARD TEH SURFACE...HELPING TO SCOUR OUT THE LOW 
LEVEL MOISTURE.

RESPITE FROM THE ADVERSE AVIATION CONDITIONS WILL BE BRIEF AS A 
DEVELOPING LOW PRESSURE SYSTEM OVER THE NORTHERN GULF WILL BEGIN TO 
LIFT NE ALONG THE GA-SC COAST TONIGHT. THIS WEATHER SYSTEM WILL 
SPREAD ADDITIONAL MOISTURE LEADING TO WIDESPREAD MVFR/IFR CEILINGS 
ALONG WITH WIDESPREAD RAIN. THE ADVERSE AVIATION WEATHER CONDITIONS 
WILL PERSISTS INTO MONDAY MORNING.

THE RAIN WILL DIMINISH MONDAY AFTERNOON-MONDAY NIGHT THOUGH 
EXTENSIVE CLOUDINESS EXPECTED TO PERSIST. ANOTHER LOW PRESSURE 
SYSTEM WILL AFFECT CENTRAL NC LATE TUESDAY INTO WEDNESDAY...BRINGING 
A ROUND OF HEAVY SHOWERS AND POSSIBLY A FEW THUNDERSTORMS. SFC WINDS 
WILL BECOME WEDNESDAY THROUGH CHRISTMAS DAY WITH WIND GUSTS 30-35KTS 
PROBABLE.


&&

.RAH WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$ 

SYNOPSIS...WSS
NEAR TERM...WSS
SHORT TERM...CBL
LONG TERM...WSS
AVIATION...WSS



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