FXUS62 KRAH 051800
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
100 PM EST SAT DEC 05 2009

.SYNOPSIS...
LOW PRESSURE CENTERED NEAR THE NC OUTER BANKS THIS AFTERNOON WILL 
INTENSIFY AND TRACK NORTHEASTWARD OFFSHORE THE MID ATLANTIC AND NEW 
ENGLAND COASTS THROUGH TONIGHT. MEANWHILE... COLD HIGH PRESSURE WILL 
BUILD IN FROM THE WEST AND LINGER THROUGH SUNDAY NIGHT.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 1128 AM SATURDAY...

NO SIGNIFICANT FORECAST UPDATE MADE OR NECESSARY BASED ON THE 
LATEST OBSERVATIONAL AND MODEL DATA THIS MORNING. WE STILL EXPECT 
PERIODS OF MAINLY LIGHT RAIN AND DRIZZLE TO MIX WITH OR BRIEFLY 
CHANGE TO SNOW MAINLY WEST/NORTH OF INTERSTATE 85 LATE THIS 
AFTERNOON THEN EASTWARD INTO THE NORTHERN COASTAL PLAIN THIS 
EVENING. LITTLE (ON GRASSY AND ELEVATED SURFACES SUCH AS CAR TOPS) 
TO NO ACCUMULATION EXPECTED. 

THE H85 LOW WAS LOCATED NEAR HICKORY PER THE 12Z RAOB ANALYSIS. 
BENEATH DCVA FORCING FOR ASCENT ATTENDANT THE PRIMARY UPPER S/W 
TROUGH OVER THE TN VALLEY... THE H85 SOUTHEAST FLOW ALONG-AHEAD OF 
THE LOW TRACK WILL CONTINUE TO PROMOTE ISENTROPIC UPGLIDE/WAA AND 
ENHANCED FGEN OVER THE NORTHERN NC PIEDMONT NORTHWARD INTO CENTRAL 
VA TODAY. NOT SURPRISINGLY... THOSE LOCATIONS HAVE BEEN WHERE 
STRONGER RADAR RETURNS AND PRECIPITATION RATES (UPWARD OF FIVE 
HUNDREDTHS TO ONE TENTH OF AN INCH AT DANVILLE VA) HAVE BEEN FOUND 
THE LAST SEVERAL HOURS. ALSO OF INTEREST IS THAT THE RAIN HAS 
ALREADY CHANGED TO SNOW AS FAR SOUTHEAST AS LYNCHBURG AND LOUISA VA. 

WE STILL EXPECT THE MID LEVEL DEFORMATION BAND OVER AND JUST 
UPSTREAM OF THE BLUE RIDGE TO CONTINUE TO PIVOT EAST AND MERGE WITH 
THE AFOREMENTIONED LOWER LEVEL-FORCED PRECIPITATION. THE RESULT WILL 
BE CONTINUED GENERALLY LIGHT BUT STEADY RAIN AND DRIZZLE... WITH THE 
GREATEST LIQUID EQUIVALENT AMOUNTS OF ONE TO TWO TENTHS OF AN INCH 
OVER THE NORTHERN COUPLE OF TIER OF NC COUNTIES... TO ONLY A TRACE 
TO A FEW HUNDREDTHS WHERE ISENTROPIC DOWNGLIDE (SOUTH OF THE H85 
LOW) HAS ALREADY DEVELOPED OVER THE SOUTHERN PIEDMONT. THE FORECAST 
THERMAL PROFILE WOULD SUPPORT RAIN MIXED WITH AND BRIEFLY CHANGING 
TO SNOW -- MAINLY FROM THE TRIAD TO CHAPEL HILL TO ROANOKE RAPIDS 
AND POINTS NW) -- BUT CLOUD MICROPHYSICS AND MARKED DRYING ALOFT 
APPROACHING FROM THE UPSTATE OF SC WILL LIMIT SATURATION IN THE 
BERGERON/SNOW GROWTH LAYER. THAT FACTOR... IN ADDITION TO THE 
LIMITED LIQUID EQUIVALENT AMOUNTS BY THE TIME THE COLD AIR ARRIVES 
AND THE RELATIVELY WARM AND WET GROUND CONTINUE TO ARGUE FOR A 
RELATIVE SNOW NON-EVENT THIS TIME AROUND. 

WITH THE PRECIP... THICK CLOUD COVER... AND NEUTRAL THERMAL 
ADVECTION THROUGH MUCH OF THE DAY... TEMPS SHOULD MOVE MINIMALLY 
TODAY. EXPECT HIGHS OF 45-53. WITH RAPID CLEARING TAKING PLACE FROM 
03Z-07Z AND COLD ADVECTION... WE SHOULD SEE LOWS OF 27-33. -GIH

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
AS OF 230 AM SATURDAY...

SUNDAY AND SUNDAY NIGHT:
A COLD DRY SURFACE HIGH IS EXPECTED TO SETTLE ACROSS CENTRAL NORTH 
CAROLINA ON SUNDAY... WITH A WEST-SOUTHWESTERLY FLOW ALOFT. THIS 
WILL ALLOW FOR MOSTLY SUNNY SKIES TO BECOME PARTLY SUNNY BY LATE IN 
THE DAY... AS HIGH LEVEL CLOUDINESS BEGINS TO FILTER INTO THE AREA. 
NW WINDS TO START THE DAY WILL BECOME LIGHT AND VARIABLE... AS THE 
HIGH SETTLES ACROSS THE AREA. AFTERNOON LOW LEVEL THICKNESS VALUES 
ARE EXPECTED TO GENERALLY RANGE FROM 1305 TO 1315 METERS... ROUGHLY 
15 TO 20 METERS BELOW NORMAL AND ABOUT 5 METERS COOLER THAN 
YESTERDAYS MODEL RUNS FOR SUNDAY. THUS... EXPECT HIGH TEMPS... EVEN 
WITH MOSTLY SUNNY SKIES FOR A GOOD PART OF THE DAY... TO BE 
GENERALLY IN THE MID TO UPPER 40S... WITH PERHAPS A FEW LOWER 50S IN 
THE SOUTHEAST.

THE SURFACE HIGH IS EXPECT TO SHIFT OFFSHORE ON SUNDAY NIGHT/MONDAY 
MORNING... AS A WEAK COLD FRONT ASSOCIATED WITH A NORTHERN STREAM 
TROUGH APPROACHES THE AREA. THIS SHOULD HELP TO INCREASE MOISTURE 
ACROSS THE REGION A BIT ALLOWING SKIES TO BECOME/REMAIN PARTLY 
CLOUDY... WHICH SHOULD HELP KEEP LOW TEMPS FROM FALLING OFF A CLIFF. 
THUS... WITH SKIES BECOMING PARTLY CLOUDY... AND LOW LEVEL THICKNESS 
VALUES INCREASING SOME 10 TO 15 METERS OVERNIGHT... EXPECT LOWS TO 
ONLY DROP INTO THE UPPER 20S TO NEAR 30 ACROSS THE NORTH TO THE 
LOWER TO MID 30S ELSEWHERE.

MONDAY AND MONDAY NIGHT:
MODELS INDICATE A QUICK MOVING NORTHERN STREAM SHORTWAVE TRACKING 
ACROSS PORTIONS OF THE UPPER MIDWEST... GREAT LAKES... AND NEW 
ENGLAND ON MONDAY. AS THIS FEATURE QUICKLY MOVES ACROSS THE 
AFOREMENTIONED AREA... A WEAK GENERALLY DRY COLD FRONT WILL MOVE 
THROUGH CENTRAL NORTH CAROLINA ON MONDAY AFTERNOON INTO THE EVENING. 
THE GFS CONTINUES TO ATTEMPT TO GENERATE SOME LIGHT QPF WITH WAA 
AHEAD OF THE COLD FRONT... WHILE THE NAM AN EC KEEP THE AREA DRY ON 
MONDAY AND MONDAY NIGHT. GIVEN THE WESTERLY FLOW ALOFT... WILL KEEP 
THE FORECAST DRY WITH PARTLY CLOUDY SKIES. LOW LEVEL THICKNESS 
VALUES LOOK TO BE NEAR NORMAL. THUS... WILL GO WITH HIGH TEMPS NEAR 
NORMAL... LOWER TO MID 50S ACROSS THE AREA.

SKIES BEGIN TO CLEAR A BIT ON MONDAY NIGHT/TUESDAY MORNING BEHIND 
THE FRONT... AS STRONG SURFACE HIGH PRESSURE BUILD INTO THE AREA 
FROM THE NORTHWEST. HOWEVER... STILL EXPECT SKIES TO REMAIN AT LEAST 
PARTLY CLOUDY. THUS... WILL GO WITH LOW TEMPS GENERALLY IN THE MID 
TO UPPER 30S. -BSD

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
AS OF 310 AM SATURDAY...

MEDIUM RANGE MODELS ARE IN FAIRLY GOOD AGREEMENT WITH THE OVERALL 
PATTERN DURING THE EXTENDED PORTION OF THE FORECAST... WITH ANOTHER 
GOOD CHANCE FOR RAIN/SHOWERS ON TUESDAY NIGHT INTO WEDNESDAY.

TUESDAY:
A 1027 MB SURFACE HIGH IS EXPECTED TO BUILD/EXTEND INTO THE AREA 
FROM THE NORTH... PROVIDING THE AREA WITH CONTINUED COLD AIR 
ADVECTION. MEANWHILE... A POTENT UPPER LEVEL SHORTWAVE AND ATTENDANT 
SURFACE LOW ARE EXPECT TO LIFT NORTHEASTWARD OUT OF THE FOUR CORNERS 
REGION AND INTO THE PLAINS STATES. AS THIS HAPPENS AMPLE MID AND 
UPPER LEVEL MOISTURE SHOULD STREAM INTO OUR AREA... WITH MID LEVEL 
FLOW BECOMING WSW'ERLY. THIS WILL ALLOW SKIES TO BECOME MOSTLY 
CLOUDY BY LATE IN THE DAY... WITH PERHAPS A FEW SPOTTY AREAS OF RAIN 
DEVELOPING ACROSS WESTERN PORTIONS OF THE AREA LATE IN THE DAY WITH 
ISENTROPIC LIFT INCREASING. AFTERNOON LOW LEVEL THICKNESS VALUES ARE 
EXPECTED TO GENERALLY RANGE FROM 1310 METERS TO 1325 METERS (NORTH 
TO SOUTH)... WHICH GIVEN THE INCREASING CLOUD COVER WILL LEAD TO 
HIGH TEMPS IN THE UPPER 40S TO NEAR 50 ACROSS THE NORTH... TO LOWER 
TO MID 50S... ELSEWHERE.

TUESDAY NIGHT THROUGH WEDNESDAY NIGHT:
THE POTENT MID LEVEL S/W AND ATTENDANT SURFACE LOW ARE EXCEPTED TO 
TRACK INTO THE MIDWEST/GREAT LAKES REGION BY 12Z WEDNESDAY. LOW 
LEVEL SOUTHERLY FLOW JUST OFF THE SURFACE INCREASES ACROSS OUR AREA 
ON TUESDAY NIGHT/WEDNESDAY MORNING... IN RESPONSE TO THE SYSTEM. AS 
THIS HAPPENS WARM MOIST AIR IS FORECAST TO OVERRIDE THE COOL STABLE 
DOME OF AIR (PROVIDED BY THE SURFACE HIGH TO THE NORTH) WHICH WILL 
ALLOW CHANCES FOR PRECIP TO INCREASE. AS PRECIP STARTS FALLING INTO 
THE DRY AIR... THE HIGH BEGINS TO MOVE EASTWARD... ALLOWING FOR 
POSSIBLY A HYBRID DAMMING EVENT TO OCCUR ON TUESDAY NIGHT INTO 
WEDNESDAY. MODELS SOUNDINGS IN THE NORTHWEST PIEDMONT OFF OF THE GFS 
WOULD INDICATE THE POTENTIAL FOR A POSSIBLY A MIX OF SLEET AND RAIN 
AS PRECIP BEGINS... BUT QUICKLY BECOMING A COLD RAIN. HOWEVER... THE 
EC IS CONSIDERABLE WARMER AND DEPICTS ONLY RAIN ACROSS THE ENTIRE 
CWA. GIVEN WE ARE STILL SEVERAL DAYS OUT WILL KEEP EVERYTHING IN THE 
FORM OF LIQUID. HOWEVER... WITH INCREASING UPSLOPE FLOW AND 
ISENTROPIC LIFT FLOW ON TUESDAY NIGHT/WEDNESDAY MORNING WILL 
INCREASE POPS TO LIKELY ACROSS THE NORTHWEST... AND KEEP ALL OTHER 
AREA IN THE HIGH CHANCE CATEGORY. OVERNIGHT LOW WILL BE TRICKY... 
AND BE GREATLY DEPENDENT ON THE ARRIVAL OF THE QPF AND QPF AMOUNTS. 
FOR NOW WILL GO WITH MID TO UPPER 30S IN THE NORTHWEST... WITH UPPER 
30S TO LOWER 40S ELSEWHERE.

FOR WEDNESDAY... THE GFS TRIES TO DEVELOP A SECONDARY LOW ALONG THE 
COAST (MILLER B) ON WEDNESDAY MORNING... WITH THE PRIMARY/ORIGINAL 
LOW TRACKING ACROSS PORTIONS OF THE OHIO VALLEY AND INTO THE GREAT 
LAKES REGION... WHILE THE EC SHOWS A WEAKER DEPICTION OF THIS 
OCCURRING WITH THE SECONDARY LOW TRACKING FURTHER INLAND AND ACROSS 
OUR CWA. THE GEM... NOT SHOWING A SECONDARY LOW DEVELOPING ACROSS 
OUR AREA. THUS... A LOT OF UNCERTAINTY REMAINS WITH REGARDS TO HOW 
MUCH INSTABILITY AND CONVECTIVE POTENTIAL WE WILL HAVE WITH THIS 
SYSTEM. HOWEVER... IT STILL LOOK LIKE WE WILL HAVE A CONTINUED GOOD 
CHANCE FOR PRECIP THROUGH AT LEAST THE FIRST HALF OF THE DAY... 
BEFORE THE ASSOCIATED COLD FRONT CROSSES THE REGION. FOR NOW WILL GO 
WITH HIGH TEMPS ON WEDNESDAY RANGING FROM THE LOWER 50S IN THE 
NORTHWEST TO THE MID 60S IN THE SOUTHEAST.

SKIES BEGIN TO CLEAR BEHIND THE FRONT ON WEDNESDAY NIGHT/THURSDAY 
MORNING... AS THE DRIER AIR FILTERS INTO THE AREA. LOWS THURSDAY 
MORNING LOOK TO RANGE FROM THE MID 30S NW TO THE MID 40S SE.

THURSDAY THROUGH FRIDAY:
COLD SURFACE HIGH PRESSURE IS EXPECTED TO BUILD INTO THE AREA ON 
THURSDAY... WITH MOSTLY SUNNY SKIES EXPECT. LOW LEVEL THICKNESS 
VALUES ARE EXPECTED RETURN TO BELOW NORMAL VALUES... WITH THE GFS 
CONSIDERABLY COLDER THE THE EC (LOW LEVEL THICKNESS VALUES DIFFERING 
SOME 30 TO 40 METERS OR SO). THUS... FOR NOW WILL NOT GO TO WILD AND 
ADVERTISE HIGHS IN THE UPPER 40S IN THE NORTHWEST TO LOWER TO MID 
50S ELSEWHERE. THE SURFACE HIGH IS EXPECTED TO SLOWLY TRANSLATE  
ACROSS THE CWA ON THURSDAY NIGHT AND BEGINNING TO MOVE OFFSHORE BY 
FRIDAY MORNING. THUS... EXPECT LOW TEMPS TO DIP INTO THE UPPER 20S 
TO LOWER 30S.

HIGH PRESSURE MOVES OFFSHORE ON FRIDAY... AS MID/UPPER LEVEL 
MOISTURE BEGINS TO FILTER BACK INTO THE AREA AGAIN. CHANCES FOR 
PRECIP LOOK TO REMAIN TO THE WEST OF THE AREA THROUGH 00Z SATURDAY. 
HIGHS ON FRIDAY ARE EXPECTED TO BE IN THE LOWER TO MID 50S... NEAR 
NORMAL. 

&&

.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
AS OF 100 PM SATURDAY...

THE PASSAGE OF AN UPPER LEVEL DISTURBANCE COMBINED WITH MOIST 
SOUTHEASTERLY FLOW FROM THE ATLANTIC WILL RESULT IN IFR/LIFR 
CONDITIONS AT ALL CENTRAL NC TERMINAL SITES THROUGH THE EARLY-MID 
AFTERNOON.  AS COLD AIR RUSHES INTO THE REGION THROUGH THE DEPTH OF 
THE ATMOSPHERE... THE RAIN MAY MIX WITH OR CHANGE OVER TO SNOW (WITH 
ASSOCIATED REDUCED VISIBILITIES) FOR A FEW HOURS (MAINLY AT TRIAD 
TERMINALS AND PERHAPS AS FAR EAST AS RDU AND RWI). PRECIPITATION 
SHOULD END WITH A RETURN TO VFR FROM SOUTHWEST TO NORTHEAST IN 
THE 22Z TO 04Z/5TH TIME FRAME... AS COLD BUT DRY HIGH PRESSURE 
BUILDS INTO THE REGION FROM THE WEST TONIGHT AND LINGERS THROUGH 
SUNDAY.  

LOOKING BEYOND 18Z SUNDAY: THERE WILL BE ANOTHER CHANCE OF MVFR 
CONDITIONS AND A LITTLE LIGHT RAIN OR DRIZZLE... MAINLY AT EASTERN 
TERMINALS... AHEAD OF A WEAKER STORM SYSTEM ON MONDAY. AFTER A 
RETURN TO VFR FOR MONDAY NIGHT AND TUESDAY... EXPECT LIFR/IFR 
CONDITIONS AND A COLD RAIN ASSOCIATED WITH A STRONGER STORM SYSTEM 
TUESDAY NIGHT AND WEDNESDAY. 

&&

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

&&

$$

SYNOPSIS...MWS
NEAR TERM...MWS/HARTFIELD
SHORT TERM...BSD
LONG TERM...BSD
AVIATION...MWS