FXUS62 KRAH 231128
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
623 AM EST WED DEC 23 2009

.SYNOPSIS...
HIGH PRESSURE WILL EXTEND ACROSS THE REGION THROUGH THURSDAY... 
BRINGING SEASONABLY COOL AND DRY CONDITIONS. A STORM SYSTEM WILL 
APPROACH FROM THE SOUTHWEST LATE THURSDAY AND AFFECT THE AREA 
CHRISTMAS EVE THROUGH CHRISTMAS DAY.

&&

.NEAR TERM /THROUGH THURSDAY/... 
AS OF 230 AM WEDNESDAY...

TODAY AND TONIGHT: A 1035 MB HIGH CENTERED OVER THE GREAT LAKES 
REGION AND SOUTHERN CANADA WILL CONTINUE TO EXTEND SOUTHWARD INTO
OUR REGION TODAY AND TONIGHT... AS SHORTWAVE RIDGING BEGINS TO
TRANSLATE EASTWARD AND INTO OUR AREA. OTHER THAN THE POTENTIAL FOR
SOME HIGH LEVEL CIRRUS FILTERING INTO THE AREA FROM THE WEST...
EXPECTED DRY CONDITIONS TO CONTINUE... WITH SKIES GENERALLY MOSTLY
SUNNY TO AT TIMES PARTLY SUNNY (ONLY HIGH THIN CLOUDS GENERALLY)
TODAY. AFTERNOON THICKNESS VALUES ARE EXPECTED TO TOP OUT IN THE
1315 TO 1325 METER RANGE ACROSS THE AREA. GIVEN THESE THICKNESS
VALUES AND MOSTLY TO PARTLY SUNNY SKIES... EXPECT TEMPS WILL
GENERALLY BE ON THE HIGH SIDE OF STATISTICAL GUIDANCE (CLOSER TO
THE MET). THUS... EXPECT HIGH TEMPS TO RANGE FROM THE UPPER 40S TO
AROUND 50 ACROSS THE NORTH... TO THE LOWER TO POSSIBLY MID 50S
ACROSS THE SOUTH. WEAK WAA IN THE LOW LAYERS TONIGHT MAY PRODUCE
SOME PATCHES OF LOW STRATUS TONIGHT... WITH THE BEST POTENTIAL IN
THE NORTHWEST THANKS TO WEAK UPSLOPE FLOW. THIS SLIGHT INCREASE IN
MOISTURE SHOULD HELP KEEP TEMPS UP A BIT OVERNIGHT. THUS... EXPECT
LOW TEMPS WILL GENERALLY RANGE FROM THE UPPER 20S ACROSS THE NORTH
TO THE LOWER 30S ACROSS THE SOUTH.

THURSDAY: SURFACE HIGH PRESSURE WILL CONTINUE TO EXTEND INTO THE 
AREA FROM THE NORTH... WITH THE MID LEVEL SHORTWAVE RIDGE AXIS 
BEGINNING TO SHIFT TO THE EAST OF THE AREA BY AFTERNOON ON THURSDAY 
AS A STORM SYSTEM MOVES INTO THE CENTRAL PORTION OF THE COUNTRY. 
THIS SHOULD ALLOW MID AND HIGH LEVEL MOISTURE TO INCREASE ACROSS OUR 
AREA... AS FLOW ALOFT BECOMES SOUTHWESTERLY. AFTERNOON LOW LEVEL 
THICKNESS VALUES ARE PROGGED TO BE A FEW METERS HIGHER THAN EXPECTED 
VALUES OF TODAY. HOWEVER... GIVEN THE INCREASE IN CLOUD COVER IN THE 
AFTERNOON... EXPECT TEMPS MAY BE A DEGREE OR TWO COOLER THAN 
EXPECTED VALUES OF TODAY. THUS... EXPECT HIGH TEMPS IN THE MID TO 
UPPER 40S ACROSS THE NORTH TO LOWER 50S ACROSS THE SOUTH... WITH 
CONTINUED DRY CONDITIONS.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY NIGHT/... 
AS OF 230 AM WEDNESDAY...

..A THREAT OF SEVERAL HOURS OF LIGHT FREEZING RAIN AT THE ONSET OF 
PRECIPITATION OVER THE NW PIEDMONT LATE THURSDAY NIGHT... BEFORE A
TRANSITION TO ALL LIQUID BY FRIDAY MORNING...

THURSDAY NIGHT (CHRISTMAS EVE): THE 1038 MB SURFACE HIGH WILL BE
CENTERED NORTH OF THE GREAT LAKES EXTENDING SOUTH DOWN THE EAST
COAST WITH A CAD WEDGE IN PLACE THURSDAY EVENING. GIVEN THE
NORTHWEST DISPLACEMENT OF THE SURFACE HIGH DO NOT EXPECT THE AIR IN
THE LOW LEVELS TO BE PARTICULARLY DRY WITH DEWPOINTS MAINLY IN THE
MIDDLE 20S PRIOR TO ONSET OF PRECIP. MODEL WET BULB ZERO FOR
06-12Z FRI REMAINS OVER THE NW PIEDMONT AND VA BORDER COUNTIES
SUGGESTING THE POTENTIAL FOR THE PRECIP TO BEGIN AS PERIOD OF LIGHT
FREEZING RAIN AFTER MIDNIGHT THURSDAY NIGHT/FRIDAY MORNING. BEST
ISENTROPIC LIFT DOES NOT GET GOING WITH THE INCREASING 40 KT LOW
LEVEL FLOW UNTIL 06Z AND LATER. WILL KEEP A MENTION OF LIGHT
FREEZING RAIN EARLY OVER THE TRIAD AND WELL NORTH OF RALEIGH WHERE
THERE IS A POTENTIAL FOR A LIGHT GLAZE PRODUCED BY THE FIRST
TENTH OF AN INCH OF PRECIPITATION. ALL MODELS SUGGEST A TRANSITION
OVER TO ALL LIQUID BY AROUND DAYBREAK AS THE SURFACE LOW LIFTS
NORTH TOWARD OUR REGION AND A COASTAL FRONT PUSHES INTO THE
COASTAL PLAIN. A WINTER WEATHER ADVISORY MAY BE NEEDED FOR THE NW
PIEDMONT COUNTIES EARLY FRIDAY MORNING. LOWS FROM A DEGREE OR TWO
BELOW FREEZING NORTHWEST... TO AROUND 40 DEGREES OR SO SE... WITH
A GRADUAL RISE IN TEMPERATURES EXPECTED OVERNIGHT.

FRIDAY AND FRIDAY NIGHT (CHRISTMAS): EXPECT THE DEEP ISENTROPIC
LIFT TO PROVIDE WIDESPREAD RAINFALL SPREADING IN FROM THE SW TO NE
ACROSS ALL OF CENTRAL NC. WILL KEEP CATEGORICAL CHANCE OF SHOWERS
ON FRIDAY. MODELS TRACK THE SURFACE MILLER-B TYPE LOW INLAND JUST
EAST OF THE I-95 CORRIDOR. THIS FOCUS WILL ALLOW FOR LONG PERIODS
OF MODERATE RAINFALL WITH QPF AMOUNTS AROUND TO JUST OVER ONE INCH
ACROSS MOST OF THE AREA. WHILE MARITIME TROPICAL LOW LEVEL THETA-E
AND ASSOCIATED SUFFICIENT SURFACE BASED INSTABILITY SHOULD REMAIN
OFFSHORE GIVEN THE EXPECTED TRACK OF THE TRIPLE POINT THERE IS
SOME CONCERN FOR ELEVATED CONVECTION. THE PATTERN WILL BE SUPPORTIVE
OF POTENTIAL (CONVECTIVE) INSTABILITY...OWING TO THE OVERRUNNING
OF THE MID LEVEL DRY SLOT ATOP UNSTABLE PARCELS ORIGINATING IN
SOUTHEASTERLY FLOW AROUND H85. THE ONLY LACKING ELEMENT IS STRONG
UPPER DYNAMICS AS THE BEST UPPER SUPPORT FOR CONVECTION REMAINS NE
OF THE AREA. WILL MAINTAIN ISOLATED THUNDER OVER ROUGHLY THE
EASTERN THIRD OF THE CWA (ALONG THE AXIS OF THE SOUTHEASTERLY H85
JET. HIGHS FRIDAY COULD RANGE DRAMATICALLY WITH COOL AIR LOCKED IN
THE TRIAD AND WARMER MARITIME AIR REACHING INTO THE SANDHILLS AND
COASTAL PLAIN. HIGHS IN THE MID 40S OVER THE RESIDUAL LY- WEDGED
NW PIEDMONT TO NEAR 60 EAST OF THE WEDGE FRONT WARM SECTORED SE.

DRYING... COOLING... AND CLEARING FRIDAY NIGHT... AS THE SYSTEM
PIVOTS NORTHEASTWARD AND AWAY FROM CENTRAL NC. LOWS IN THE MIDDLE
30S WEST TO MIDDLE 40S EAST WITH LINGERING CLOUD COVER ESPECIALLY
IN THE EAST.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
AS OF 230 AM WEDNESDAY...

SATURDAY THROUGH TUESDAY: THIS PERIOD WILL BE DOMINATED BY A COLD 
POLAR VORTEX OVER THE GREAT LAKES/NEW ENGLAND. ANY PRECIPITATION IS 
EXPECTED TO REMAIN CONFINED TO UPSLOPE REGIONS IN THE CENTRAL 
APPALACHIANS... THOUGH WE WILL NEED TO MONITOR THE MAGNITUDE OF S/W 
TROUGHS THAT MAY PIVOT AROUND THE BASE OF THE VORTEX ON SUNDAY AND 
ESPECIALLY MONDAY WHEN THE BEST DYNAMICS WITH THE UPPER LOW MOVE 
THROUGH. SOME FLURRIES OR LIGHT SNOW COULD DEVELOP MONDAY BUT WILL 
DEPEND ON THE AMOUNT OF MOISTURE AVAILABLE IN THE NW FLOW. HIGHS AND 
LOWS IN THE 40S AND 20S RESPECTIVELY... ABOUT A CATEGORY BELOW 
NORMAL.

&&

.AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
AS OF 620 PM WEDNESDAY...

VFR CONDITIONS WILL GENERALLY CONTINUE THROUGH THE 24 TAF PERIOD... 
WITH POSSIBLY SOME MVFR CIGS AND/OR VISBYS IN THE NORTHWEST PIEDMONT 
NEAR SUNRISE ON THURSDAY.

HIGH PRESSURE LOCATED OVER SOUTHERN ONTARIO AND THE GREAT LAKES 
REGION... WILL CONTINUE TO EXTEND INTO CENTRAL NORTH CAROLINA TODAY.
THE ACCOMPANYING DRY AIR MASS WILL ENSURE VFR CONDITIONS TODAY  
THROUGH AT LEAST 06Z THURSDAY. OTHERWISE... SCATTERED TO AT TIMES 
BROKEN HIGH CLOUDS WILL STREAM INTO THE AREA IN THE WESTERLY FLOW 
ALOFT TODAY AND TONIGHT... WITH CALM WINDS THIS MORNING BECOMING 
LIGHT NORTHEASTERLY BY 15Z OR SO.

WE MAY SEE SOME STRATUS DEVELOP THURSDAY MORNING AS 925MB EASTERLY 
FLOW JUST ABOVE THE SURFACE WILL OVERSPREAD SOME ATLANTIC MARITIME 
AIR INTO THE STATE. HOWEVER... WILL ONLY INTRODUCE A TEMPO GROUP AT 
KGSO AND KINT FOR THE POTENTIAL FOR MVFR CIGS AND/OR VISBYS AFTER 
08Z THURSDAY... AS THE FLOW REMAINS FAIRLY WEAK (NW TAF SITES LOOKS 
TO STAND THE BEST CHANCE GIVEN THE AID FROM UPSLOPE FLOW).

A STORM SYSTEM WILL APPROACH NC FROM THE WEST-SOUTHWEST AND BRING 
MVFR/IFR CONDITIONS THURSDAY NIGHT AND INTO FRIDAY. THERE IS ALSO 
THE POTENTIAL FOR LOW LEVEL WIND SHEAR CONDITIONS THURSDAY 
NIGHT/FRIDAY MORNING FROM A 40 TO 45KT SELY LLJ. VFR CONDITIONS ARE 
EXPECTED TO RETURN ON SATURDAY AS THE STORM SYSTEM EXITS THE AREA.

&&

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

&&

$$
SYNOPSIS...JO
NEAR TERM...BSD
SHORT TERM...JO
LONG TERM...JO
AVIATION...BSD