FXUS62 KRAH 051135
AFDRAH
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
635 AM EST SAT DEC 05 2009
.SYNOPSIS...
A SURFACE LOW PRESSURE CENTER WILL DEVELOP OFF THE SOUTHEAST COAST
THIS MORNING... AND MOVE QUICKLY NORTHEAST ALONG THE NORTH CAROLINA
COAST THROUGH THIS AFTERNOON. WIDESPREAD RAIN WILL CONTINUE OVER
MUCH OF THE AREA THROUGH THE AFTERNOON... AND MAY MIX WITH OR CHANGE
OVER TO A LITTLE WET SNOW OVER THE FAR NORTHERN PIEDMONT OF NORTH
CAROLINA BEFORE ENDING BY LATE EVENING. CHILLY HIGH PRESSURE WILL
BUILD IN FROM THE WEST LATE TONIGHT THROUGH SUNDAY.
&&
.NEAR TERM /THROUGH TONIGHT/...
AS OF 245 AM SATURDAY...
IN SHORT... THE OVERALL EXPECTATIONS OF WIDESPREAD RAIN TODAY...
MIXING WITH OR CHANGING BRIEFLY TO WET SNOW OVER THE NORTHERN
PIEDMONT BEFORE ENDING LATE AFTERNOON AND EARLY EVENING... STILL
LOOK REASONABLE.
THE LATEST SURFACE ANALYSIS SHOWS TWO BAGGY AREAS OF LOW PRESSURE...
ONE OVER THE NORTHEAST GULF AND ANOTHER OFF THE GA/SC COAST. A
STRONG SHORTWAVE TROUGH WAS SEEN CLEARLY IN WATER VAPOR IMAGERY
SWINGING THROUGH THE LOWER MISS VALLEY AND INTO NORTHERN MS/WEST TN.
AS THIS VORTICITY MAXIMUM APPROACHES... THE RIGHT ENTRANCE REGION OF
AN INTENSE 190+ KT UPPER JET CORE OVER MAINE AND THE CANADIAN
MARITIMES PASSES OVERHEAD AND PROMOTES VIGOROUS ASCENT... FOSTERING
STRONG DYNAMIC LIFT AND SURFACE CYCLONE INTENSIFICATION OFF THE
CAROLINA COAST THIS AFTERNOON. THE VORTICITY MAXIMUM THEN SHOOTS
EAST-NORTHEAST INTO NC LATE THIS AFTERNOON THEN EXITS QUICKLY IN THE
EARLY EVENING... WITH THE SURFACE LOW HEADING NORTHEAST AWAY FROM
THE NORTHERN OUTER BANKS... ALLOWING COLDER AIR TO RUSH IN BOTH IN
THE LOWER AND MID LEVELS. EARLIER FORECASTS HAVE REFLECTED THIS
SCENARIO... AND LITTLE HAS CHANGED IN THE LATEST MODEL GUIDANCE AND
SHORT TERM TRENDS THAT INDICATES A NEED FOR SIGNIFICANT CHANGE.
THUS... WILL MAKE VERY FEW ALTERATIONS TO THE PRECIP FORECAST INTO
TONIGHT.
THE WRF-NMM FROM SPC AND THE ECMWF APPEAR TO BE BEST HANDLING THE
CURRENT PRECIP SHIELD... INCLUDING THE BAND OF A BIT HEAVIER PRECIP
THAT PASSED QUICKLY OVER THE COASTAL PLAIN OVER THE LAST FEW HOURS.
AS SURFACE PRESSURES FALL NEAR THE COAST WITH STRONG MID LEVEL
HEIGHT FALLS (120 M FROM 12Z-00Z)... AND AS 925-850 MB HEIGHTS FALL
OVER THE WESTERN/CENTRAL CAROLINAS THIS MORNING... LIFT THROUGH THE
COLUMN WILL DEEPEN AS LOW LEVEL MASS CONVERGENCE AUGMENTS STRONG
LIFT INDUCED BY MID LEVEL DPVA AND UPPER LEVEL DIVERGENCE. EXPECT
SOLID RAIN COVERAGE CWA-WIDE BY MID MORNING CONTINUING THROUGH
AFTERNOON. THE FAR WESTERN PIEDMONT... TO THE NORTHWEST OF THE 925
MB TROUGH... MAY NOT SEE QUITE THE DEGREE OF LOW LEVEL ISENTROPIC
UPGLIDE AS THE NORTHEAST CWA... AND EXPECT A BIT LOWER PRECIP
AMOUNTS HERE THROUGH THE AFTERNOON. THE 700 MB TROUGH SHIFTS INTO
CENTRAL NC/VA BY 21Z AS THE DEEPENING SURFACE AND 850 MB LOWS
DEPART... ALLOWING THE ENSUING NORTHWEST AND NORTH WINDS TO PULL IN
COLDER THICKNESSES. GIVEN THIS SINGLE-SURFACE-LOW SYSTEM AND THE
PATTERN OF ARRIVAL OF THE COLDER AIR... A MIX OR CHANGEOVER TO WET
SNOW LASTING FOR 3-5 HOURS IS STILL EXPECTED... UNTIL THE 700 MB
SHORTWAVE TROUGH HEADS TO OUR NORTHEAST AND THE DEFORMATION ON ITS
NORTHWEST SIDE WANES. WE DO START TO LOSE SATURATION IN THE CRYSTAL
GROWTH ZONE ALOFT AS THE MID/UPPER DRY PUNCH NOTED ON WATER VAPOR
IMAGERY OVER THE NORTHWEST GULF ARRIVES AFTER 00Z. THIS WILL LIMIT
THE TIME WINDOW OF OPPORTUNITY FOR ANY DECENT SNOWFALL... WITH ONLY
A FEW HOURS BETWEEN THE ARRIVAL OF SUFFICIENTLY COLD AIR AND THE
DRYING ALOFT. WOULD STILL EXPECT TO SEE A VERY LIGHT ACCUMULATION ON
GRASSY SURFACES ONLY (DUE TO THE RELATIVELY WARM PAVEMENT) WELL
NORTHWEST OF I-85... FROM KERR LAKE TO ROXBORO TO STOKESDALE... BUT
CONSIDERING THE SHORT WINDOW OF OPPORTUNITY AND THE FACT THAT THE
SWIFT MOVEMENT OF THIS SYSTEM WILL LIMIT PRECIP AMOUNTS ANYWAY...
ACCUMULATION IF ANY WILL BE INCONSEQUENTIAL.
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 /12Z SATURDAY THROUGH WEDNESDAY/...
AS OF 635 AM FRIDAY...
IFR/LIFR CONDITIONS WILL PERSIST AT ALL CENTRAL NC TERMINAL SITES
THROUGH THE EARLY-MID AFTERNOON TODAY... FOLLOWED BY AN IMPROVEMENT
TO VFR 00Z-05Z THIS EVENING/TONIGHT.
LOW PRESSURE CENTERS SITTING OVER THE NORTHEAST GULF OF MEXICO AND
OFF THE GA/SC COAST WILL TRACK NORTHEAST AND CONCENTRATE INTO ONE
DISCRETE LOW OFF THE NC COAST TODAY. STRONG LIFT MECHANISMS AND
PLENTY OF AVAILABLE MOISTURE WILL GENERATE WIDESPREAD RAIN THROUGH
TODAY.... ALONG WITH A NORTH BREEZE INCREASING THIS AFTERNOON TO
SUSTAINED 9-13 KTS. THE WORST CONDITIONS IN TERMS OF MORE MODERATE
RAIN AND LOWER VSBYS WILL BE AT RWI/FAY/RDU. IFR/LIFR CONDITIONS ARE
EXPECTED TO DOMINATE THROUGH THE AFTERNOON... THEN AS THE SURFACE
LOW SHIFTS NORTHEAST AWAY FROM THE NC COAST AND SURFACE WINDS BECOME
MORE NORTH-NORTHWEST... COLDER AIR WILL ARRIVE AND THE COLD RAIN MAY
MIX WITH OR CHANGE OVER TO WET SNOW BEFORE ENDING LATE THIS
AFTERNOON THROUGH EARLY EVENING. ANY ACCUMULATION WILL BE VERY LIGHT
ON THE GRASSY SURFACES ONLY... AND THE BEST CHANCES WILL BE NORTH OF
INT/GSO/RDU. SKIES SHOULD BEGIN TO CLEAR AFTER 00Z... FIRST AT
FAY... THEN AT INT/GSO... THEN LAST AT RDU/RWI... WITH DIMINISHING
WINDS TO LIGHT FROM THE NORTH-NORTHWEST.
LOOKING BEYOND TONIGHT: VFR CONDITIONS WILL HOLD AT LEAST INTO
MONDAY. A FAST MOVING AND WEAK DISTURBANCE MAY BRING BRIEF MVFR
CONDITIONS ON MONDAY. VFR WEATHER WILL RETURN FOR MONDAY
NIGHT/TUESDAY... THEN ANOTHER STRONGER STORM SYSTEM MAY BRING
IFR/LIFR CONDITIONS AND MORE COLD RAIN FOR TUESDAY NIGHT/WEDNESDAY.
-GIH
&&
.RAH WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SYNOPSIS...HARTFIELD
NEAR TERM...HARTFIELD
SHORT TERM...BSD
LONG TERM...BSD
AVIATION...HARTFIELD
