FXUS62 KRAH 240250
AFDRAH
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
950 PM 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 950 PM WEDNESDAY...
THE CIRRUS HAS BEEN VERY THIN THIS EVENING ALLOWING TEMPERATURES TO
DROP INTO THE 30-37 RANGE ALREADY. WITH NEARLY CALM CONDITIONS...
DEW POINTS IN THE MID 20S... AND ONLY THIN CIRRUS UPSTREAM... EXPECT
ANOTHER 5-8 DEGREE DROP FOR MINS. LOWS OF 25-30 EXPECTED. -BADGETT
INCREASING AND THICKENING CIRRUS THURSDAY WITH CUMULUS DEVELOPING IN
THE WEST AS LOW LEVEL MOISTURE DEEPENS AND WARM ADVECTION BECOMES
STRONGER. THIS WILL HOLD DOWN TEMPERATURES A LITTLE... ESPECIALLY IN
THE WEST. AFTERNOON HIGHS MID 40S EXCEPT 50 TO 55 SOUTHEAST.
ISENTROPIC LIFT ON THE INCREASE THURSDAY NIGHT AS WINDS AT 850
MILLIBARS INITIALLY AT TEN TO THIRTY KNOTS INCREASES TO THIRTY-FIVE
TO FIFTY KNOTS OVERNIGHT. RAIN SHOULD SPREAD OVER THE WEST BEFORE
DAWN AND BECOME LIKELY IN THE TRIANGLE AND GOLDSBORO AREA BEFORE
SUNRISE FRIDAY. MODELS CONSISTENT IN SHOWING A SMALL RISK FOR
FREEZING RAIN IN THE NORTHWEST BEFORE SUNRISE. IT APPEARS ONLY TREES
AND RAISED METAL SURFACES ARE AT RISK FOR A MINIMAL GLAZE AT THIS
TIME... WITH ANY ICE MELTING AFTER SUNRISE AS WARM AIR ADVECTION
CONTINUES ALOFT AND TEMPERATURES INCH UPWARD AT THE SURFACE.
OVERNIGHT LOWS NEAR FREEZING IN THE NORTHWEST... OTHERWISE MID
30S... TO NEAR 40 IN THE EXTREME SOUTH.
&&
.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
AS OF 255 PM WEDNESDAY...
FRIDAY AND FRIDAY NIGHT (CHRISTMAS): NO SIGNIFICANT CHANGES FROM
PREVIOUS FORECAST RATIONALE. ANY FREEZING RAIN OVER THE
CLIMATOLOGICAL FAVORED NORTHWEST PIEDMONT SHOULD TRANSITION TO
ALL LIQUID BY AROUND 12Z... AS THE PROGRESSIVE AND UNFAVORABLY
DISTANT CAD HIGH (OVER NORTHERN QUEBEC) SUBMITS TO INCREASING EAST
SOUTHEASTERLY FLOW AHEAD OF AN APPROACHING FRONTAL WAVE FROM
CENTRAL GA/SC. DEEP ISENTROPIC LIFT SHOULD PROVIDE FOR CATEGORICAL
SHOWERS ON FRIDAY... AS THE WARM CONVEYOR BELT PIVOTS EAST ACROSS
THE STATE. WHILE MARITIME TROPICAL LOW LEVEL THETA-E AND ASSOCIATED
SUFFICIENT SURFACE BASED INSTABILITY SHOULD REMAIN OFFSHORE GIVEN
THE EXPECTED TRACK OF THE TRIPLE POINT -- THROUGH THE EASTERN
PIEDMONT OR COASTAL PLAIN -- THERE REMAINS SOME CONCERN FOR
ELEVATED CONVECTION FRIDAY AFTERNOON... WHEN THE GFS INDICATES UP
TO SEVERAL THOUSAND J/KG OF MUCAPE ACROSS CENTRAL NC.
FURTHERMORE... THE PATTERN WILL BE ONE SUPPORTIVE OF POTENTIAL
(CONVECTIVE) INSTABILITY... OWING TO THE OVERRUNNING OF THE MID
LEVEL DRY SLOT ATOP UNSTABLE PARCELS ORIGINATING IN SOUTHEASTERLY
FLOW AROUND H85... THEN LIFTED AND REALIZED BY WEAK HEIGHT FALLS
ALOFT AND THE EXIT REGIONS OF A PHASED POLAR AND SUBTROPICAL JET
OVER THE REGION. WILL WORD AS SHOWERS... WITH ISOLATED
THUNDERSTORMS IN THE GRIDDED AND TEXT FORECAST OVER ROUGHLY THE
SOUTHEASTERN HALF OF THE CWA (ALONG THE AXIS OF THE SOUTHEASTERLY
H85 JET). HIGHS IN THE MID 40S OVER THE RESIDUALLY-WEDGED NW
PIEDMONT TO AROUND 60 EAST OF THE WEDGE FRONT-WARM-SECTORED SE.
DRYING... COOLING... AND CLEARING (ASIDE FROM JET AXIS CIRRUS) FRIDAY
NIGHT... AS THE SYSTEM PIVOTS NORTHEASTWARD AND AWAY FROM CENTRAL
NC. LOWS IN THE MIDDLE 30S WEST TO MIDDLE TO UPPER 40S EAST.
SATURDAY AND SATURDAY NIGHT: EVEN THE SLOWER NAM/WRF INDICATES THE
THE COLD FRONT SHOULD BE EAST OF THE RAH CWA BY SATURDAY
MORNING...SO EXPECT DRYING... STABLE... GENERALLY WESTERLY FLOW FOR
THE START OF THE LAST WEEKEND OF 2009.
&&
.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
AS OF 225 PM WEDNESDAY...
SUNDAY THROUGH WEDNESDAY: THE TREND FOR THIS PERIOD HAS BEEN FOR A
FASTER DEPARTURE OFF THE NORTHERN MID ATLANTIC/NEW ENGLAND COASTS
THROUGH EARLY NEXT WEEK... OF THE DEEP VORTEX FORECAST TO EVOLVE
OVER THE CENTRAL CONUS DURING THE NEXT FEW DAYS. GIVEN THE EXPECTED
WESTERLY FLOW THROUGHOUT THE COLUMN (A RELATIVELY DRY FLOW FOR
LEEWARD LOCATIONS)... WE STILL EXPECT ANY PRECIPITATION TO REMAIN
CONFINED TO UPSLOPE REGIONS IN THE CENTRAL AND EVEN PARTS OF THE
SOUTHERN APPALACHIANS... DESPITE SOME QG FORCING FOR ASCENT
ATTENDANT THE SOUTHERN PERIPHERY OF THE VORTEX SUNDAY NIGHT AND
EARLY MONDAY. THEREAFTER... BUILDING HEIGHTS ALOFT SHOULD YIELD DRY
AND SLIGHTLY MILDER CONDITIONS THAN WAS EXPECTED 24 HOURS AGO (WHEN
IT APPEARED THE POLAR VORTEX WOULD LINGER). HIGHS AND LOWS ABOUT A
CATEGORY BELOW TO AROUND THE 30 YEAR AVERAGE... GENERALLY IN THE 40S
(TO AROUND 50 DEGREES) AND 20S RESPECTIVELY.
&&
.AVIATION /00Z THURSDAY THROUGH MONDAY/...
AS OF 630 PM WEDNESDAY...
VFR CONDITIONS WILL CONTINUE THROUGH THE 24 TAF PERIOD.
HIGH PRESSURE OVER SOUTHERN CANADA WILL NOSE DOWN INTO NORTH
CAROLINA THROUGH THURSDAY. WITH THE SURFACE RIDGE AXIS
DIRECTLY OVERHEAD...EXPECT MOSTLY CALM WINDS OVERNIGHT...PICKING UP
TO 5 TO 10KTS FROM THE NORTHEAST ON THURSDAY.
CEILINGS WILL BEGIN TO LOWER THURSDAY EVENING AS A STORM SYSTEM
APPROACHES NORTH CAROLINA FROM THE WEST SOUTHWEST. IFR TO MVFR
CONDITIONS ARE EXPECTED BY DAYBREAK FRIDAY WITH WIDESPREAD RAIN
OVERSPREADING THE AREA. KINT AND KGSO COULD SEE A BRIEF PERIOD OF
FREEZING RAIN FRIDAY MORNING...BEFORE SWITCHING OVER TO ALL RAIN.
THERE IS ALSO THE POTENTIAL FOR LOW LEVEL WIND SHEAR CONDITIONS
THURSDAY NIGHT AND FRIDAY MORNING FROM A 40 TO 45 KNOT SOUTHEASTERLY
LOW LEVEL JET. VFR CONDITIONS RETURN SATURDAY AFTER SUNRISE AS THE
STORM SYSTEM EXITS THE AREA AND CONTINUE INTO MONDAY.
&&
.RAH WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SYNOPSIS...LP
NEAR TERM...BADGETT
SHORT TERM...MWS
LONG TERM...MWS
AVIATION...CBL
