FXUS62 KRAH 242003
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
303 PM EST THU DEC 24 2009

.SYNOPSIS...
HIGH PRESSURE WILL EXTEND INTO THE REGION FROM THE NORTH THIS 
EVENING. A STORM SYSTEM WILL APPROACH FROM THE SOUTHWEST TONIGHT AND 
AFFECT THE AREA THROUGH CHRISTMAS EVENING. A DRY AND MILD AIR MASS 
WILL MOVE IN SATURDAY...THEN COOL HIGH PRESSURE WILL BUILD IN FOR 
SUNDAY THROUGH MONDAY...RETURNING TEMPERATURES TO SEASONAL NORMALS. 

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 210 PM THURSDAY...

SFC ANALYSIS THIS AFTERNOON SHOWED 993 MB LOW PRESSURE 
CENTERED IN VICINITY OF ARK-LA-TEX. 1039 MB HIGH PRESSURE WAS 
CENTERED NEAR HUDSON BAY...WITH A SFC RIDGE AXIS EXTENDING SOUTH 
THROUGH THE LOWER GREAT LAKES INTO THE MID-ATLANTIC AND CAROLINAS. 
12Z RAOB ANALYSIS SHOWED A RIDGE ALOFT EXTENDING NORTH THROUGH THE 
CAROLINAS/MID-ATLANTIC/LOWER GREAT LAKES. AN H5 LOW WAS LOCATED OVER 
CENTRAL TX...AND ANOTHER H5 LOW WAS LOCATED OVER EASTERN MONTANA. 
STRONG LOW LEVEL WARM ADVECTION WAS UNDERWAY ALONG THE CENTRAL/ 
WESTERN GULF COAST...WITH A 50 KNOT SOUTHERLY H85 JET NOTED AT LAKE 
CHARLES LA...IN THE WARM SECTOR OF THE H85 LOW CENTERED OVER 
NORTH-CENTRAL TX.

TONIGHT:
THE UPPER LOW CURRENTLY IN TX IS PROGGED TO CONTINUE AMPLIFYING/ 
LIFTING NORTHEAST INTO THE MID-MS RIVER VALLEY TONIGHT...WHILE THE 
UPPER LOW CURRENTLY OVER MONTANA CONTINUES AMPLIFYING/DIGGING 
SOUTHEAST INTO NE/KS. THE ASSOCIATED SURFACE LOW IS EXPECTED TO 
CONTINUE DEEPENING...WITH A MINIMUM CENTRAL PRESSURE OF 985-990 MB 
CENTERED NEAR THE IL/MO/IA BORDER BY 12Z FRI. WARM ADVECTION WILL 
CONTINUE TO STRENGTHEN ACROSS THE SOUTHEAST STATES AND CAROLINAS 
TONIGHT...WITH FORECAST SOUNDINGS SHOWING LOW LEVEL SATURATION BY 
03-06Z (~MIDNIGHT) ACROSS THE ENTIRE AREA AS LOW LEVEL FLOW BECOMES 
SOUTHEASTERLY OFF THE ATLANTIC...OVERRUNNING THE RELATIVELY COOL/DRY 
AIRMASS IN PLACE (ASSOC/W HIGH PRESSURE EXTENDING SOUTH INTO THE 
MID-ATLANTIC/CAROLINAS). A COLD/OCCLUDED FRONT ASSOC/W THE 
VERTICALLY STACKED LOW IN VICINITY OF IL/MO/IA IS PROGGED TO BE 
APPROACHING THE NC MOUNTAINS BY 12Z FRI...WITH A WARM FRONT JUST 
SOUTH OF THE AREA ACROSS SC AND FAR SOUTHEAST NC. LATEST MODEL 
GUIDANCE REMAINS SOMEWHAT SPLIT OVER WHETHER OR NOT WE SEE MUCH IN 
THE WAY OF MEASURABLE PRECIP BEFORE SUNRISE...PARTICULARLY IN THE 
EASTERN HALF OF THE AREA. THE LATEST 12Z 4KM WRF-NMM REFLECTIVITY 
PRODUCT APPEARS TO HAVE A PRETTY GOOD HANDLE ON CURRENT (19Z) RADAR 
TRENDS OVER THE DEEP SOUTH AND SOUTHEAST STATES...AND WILL CONTINUE 
TO TREND TOWARD THE WRF-NMM TIMING FOR THE ONSET OF PRECIPITATION. 
EXPECT TO SEE PATCHY LIGHT RAIN OR DRIZZLE DEVELOPING IN THE 
SANDHILLS AND WESTERN PIEDMONT IN ASSOC/W WARM ADVECTION PRIOR TO 
SUNRISE...WITH DRY CONDITIONS LIKELY PREVAILING IN THE TRIANGLE AND 
POINTS EAST/NE. THE BULK OF PRECIPITATION ASSOC/W THE APPROACHING 
COLD/OCCLUDED FRONT SHOULD GENERALLY REMAIN WEST OF CENTRAL NC 
THROUGH SUNRISE. WILL SHOW LIKELY (60%) POPS IN THE WESTERN PIEDMONT 
JUST PRIOR TO SUNRISE...WITH SLIGHT CHANCE EAST TO THE TRIANGLE 
AREA. 

THE LATEST 12Z NAM BUFR SOUNDINGS CONTINUE TO INDICATE A POTENTIAL 
FOR LIGHT FREEZING RAIN OR DRIZZLE PRIOR TO/UP TO ~SUNRISE IN THE 
TRIAD AREA...HOWEVER...12Z GFS BUFR SOUNDINGS WOULD MOST LIKELY 
INDICATE JUST RAIN AT ~33F. WHETHER OR NOT GSO/INT SEE A PERIOD OF 
-FZRA WILL HIGHLY DEPEND ON TEMPERATURE/DEWPOINT TRENDS OVERNIGHT 
(WHERE THE WETBULB ZERO LINE ENDS UP)...AND THE TIMING OF 
PRECIPITATION MOVING INTO OR DEVELOPING OVER THE AREA. TEMPERATURE 
TRENDS WILL BE HIGHLY SENSITIVE TO THE TIMING/ONSET OF BROKEN/ 
OVERCAST LOW CEILINGS. HAVE DECIDED TO KEEP A MENTION OF RAIN *OR* 
FREEZING RAIN IN FORSYTH/GUILFORD COUNTIES PRIOR TO SUNRISE. EVEN IF 
-FZRA WERE TO OCCUR...AND EVEN IF IT DID NOT QUICKLY BECOME 
SELF-LIMITING...WARM ADVECTION IS PROGGED TO BE OVERWHELMING BY OR 
SHORTLY AFTER 12Z...WITH THERMAL PROFILES SUPPORTIVE OF ALL RAIN AT 
GSO/INT BY THAT TIME. GIVEN THAT GROUND TEMPERATURES ARE CURRENTLY 
IN THE UPPER 30S TO LOWER 40S...IT SHOULD BE DIFFICULT FOR ANY LIGHT 
FZRA TO CAUSE MUCH OF A PROBLEM...ASIDE FROM A TRACE ON ELEVATED 
METAL SURFACES AND PERHAPS A FEW ISOLATED SLICK SPOTS ON 
BRIDGES/OVERPASSES. GIVEN THE RELATIVELY BRIEF NATURE OF THE 
THREAT...AND CONTINUED UNCERTAINTY...WILL BALK AT ISSUING AN FZRA 
ADVISORY AND CONTINUE TO MENTION THE POSSIBILITY OF A BRIEF PERIOD 
OF -FZRA IN THE HAZARDOUS WEATHER OUTLOOK. LOWS TONIGHT EXPECTED TO 
RANGE FROM THE LOWER 30S IN THE FAR N/NW TO LOWER 40S IN THE FAR 
S/SE. -VINCENT

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
AS OF 300 PM THURSDAY...

CHRISTMAS DAY: 
THE TWO DISTINCT UPPER LOWS NOTED IN WV IMAGERY AND RUC DATA ARE 
PROGGED TO MERGE TOGETHER INTO ONE INTENSE UPPER LOW OVER EASTERN 
NE/KS AND WESTERN IA/MO FRIDAY AFTERNOON...WITH THE DEEP SURFACE LOW 
BECOMING VERTICALLY STACKED OVER THE MID-MS RIVER VALLEY AND 
RETROGRADING NORTHWESTWARD INTO IOWA FRIDAY AFT/EVE. THE COLD/ 
OCCLUDED FRONT ASSOC/W THIS DEEP LOW WILL APPROACH CENTRAL NC FROM 
THE WEST AROUND SUNRISE...WHILE A WARM FRONT APPROACHES FROM THE 
SOUTH. A WEAK WAVE OF LOW PRESSURE IS PROGGED TO DEVELOP ALONG THE 
OCCLUDED/WARM FRONT IN VICINITY OF CHARLOTTE...WITH THE SURFACE LOW 
TRIPLE POINT MOVING NORTHEAST DIRECTLY THROUGH CENTRAL NC FRIDAY 
AFT/EVE.

TEMPERATURES:
THIS TYPE OF SETUP MAKES FOR A CHALLENGING TEMPERATURE FORECAST. 
BASED ON THE LATEST MODEL GUIDANCE...EXPECT HIGH TEMPS TO SURGE INTO 
THE MID/UPPER 50S ALONG/EAST OF HIGHWAY 1 IN VICINITY OF THE LOW 
TRACK...WITH LOWER 60S IN THE SE COASTAL PLAIN. IN THE NW 
PIEDMONT...EXPECT THE CAD WEDGE TO HOLD FAIRLY WELL...WITH HIGHS IN 
THE MID/UPPER 40S IN THE TRIAD. THERE WILL LIKELY BE A FAIRLY TIGHT 
GRADIENT IN TEMPS IN BETWEEN THE TRIANGLE-TRIAD.

PRECIPITATION CHANCES/AMOUNTS:
WILL CONTINUE TO ADVERTISE CATEGORICAL POPS (80-100%). LATEST MODEL 
GUIDANCE INDICATES STRONG WARM ADVECTION DURING THE DAY FRIDAY... 
WITH PLENTY OF MOISTURE STREAMING INTO THE AREA OFF THE ATLANTIC 
(PWAT VALUES PROGGED AT 1.00-1.50"...OR 300-500% OF NORMAL) AND 
EXCELLENT LOW LEVEL CONVERGENCE IN ASSOC/W THE WAVE OF LOW PRESSURE 
MOVING ACROSS THE AREA. EXPECT A WIDESPREAD 1.00" OF RAIN...WITH 
ISOLATED HIGHER AMOUNTS UP TO 2.00" NOT OUT OF THE QUESTION.

SEVERE WEATHER POTENTIAL:
WHILE LOW LEVEL FORCING AND MOISTURE ARE MORE THAN ADEQUATE FOR A 
SOAKING RAIN ACROSS THE AREA...THE UPPER LEVEL DYNAMICS SHOULD BE 
WELL-REMOVED FROM THE CAROLINAS...WITH THE INTENSE UPPER LOW 
CENTERED OVER THE MIDWEST...AND BARELY 30-50 METER H5 HEIGHT FALLS 
ACROSS NC...AND THAT ONLY IN WESTERN PORTIONS OF THE STATE. AN 
INTERESTING JET CONFIGURATION OVER THE DEEP SOUTH AND SOUTHEAST 
STATES COULD RESULT IN ENHANCED UPPER DIVERGENCE OVER THE CAROLINAS 
FRI AFTERNOON...POTENTIALLY PROVIDING SOME UPPER SUPPORT ACROSS 
CENTRAL NC. CANNOT RULE OUT A SHORTWAVE DISTURBANCE IN SOUTHWEST 
FLOW ALOFT EITHER. OVERALL...THOUGH...WITH THE PRIMARY UPPER LOW 
LOCATED SO FAR TO THE NORTHWEST...UPPER SUPPORT APPEARS TO BE ON THE 
MARGINAL SIDE. REGARDLESS...LOW LEVEL WIND FIELDS (PARTICULARLY IN 
VICINITY OF THE SFC LOW TRIPLE POINT)...IN ADDITION TO DEEP LAYER 
SHEAR...WOULD CERTAINLY INDICATE A POTENTIAL FOR ORGANIZED STORMS... 
EITHER DISCRETELY OR IN ASSOC/W A FORCED LINE OF CONVECTION. 
HOWEVER...AS IS TYPICALLY THE CASE THIS TIME OF YEAR...INSTABILITY 
WILL BE MARGINAL OR NON-EXISTENT...WITH VERY WEAK MID-LEVEL LAPSE 
RATES AND WIDESPREAD CLOUD COVER/LIMITED INSOLATION. AS A RESULT... 
WITH A HIGH SHEAR/LOW CAPE TYPE ENVIRONMENT...FEEL THAT THE BEST 
SHOT AT SEVERE WEATHER WILL LIKELY REMAIN TO THE SOUTH OF CENTRAL NC 
AND ALONG/OFFSHORE THE CAROLINA COAST. -VINCENT

FRIDAY NIGHT:
WITH THE SOUTHWESTERLY MID LEVEL FLOW HAVING LITTLE CROSS-FRONTAL 
COMPONENT AND THE LACK OF AN IMMEDIATE UPSTREAM COLD AIR MASS TO 
PROPEL THE COLD FRONT ACROSS CENTRAL NC FRIDAY NIGHT...IT SHOULD 
TAKE SOME TIME FOR THE COOLER AIR TO ARRIVE...WHICH IS REFLECTED IN 
THE NAM'S SLOWER DROP IN THICKNESSES. HAVE RAISED LOWS A BIT TO 
37-52 WEST TO EAST.

FOR SATURDAY/SATURDAY NIGHT: FORECAST SOUNDINGS SHOW A SUBSTANTIAL 
LOW LEVEL INVERSION DEVELOPING WITH QUITE A BIT OF NEAR-SURFACE 
MOISTURE SATURDAY MORNING... AND THIS ALONG WITH A CONTINUOUS STREAM 
OF HIGH CLOUDS WITH FAST UPPER LEVEL FLOW SHOULD KEEP PARTLY TO 
MOSTLY CLOUDY SKIES IN THE MORNING WITH INCREASING SUNSHINE AS 
MIXING COMMENCES BY MIDDAY. AS NOTED ABOVE... LOW LEVEL THICKNESSES 
DO NOT DROP OFF DRASTICALLY UNTIL SATURDAY NIGHT... AND ABOVE-NORMAL 
VALUES SATURDAY INDICATE HIGHS OF 52-62... A SLIGHT UPTICK FROM 
PREVIOUS FORECAST HIGHS. EXPECT MOSTLY CLEAR SKIES SATURDAY NIGHT 
WITH MODIFIED HIGH PRESSURE BUILDING IN FROM THE SOUTHWEST... 
ALTHOUGH LIGHT WINDS AND ANY RESIDUAL GROUND MOISTURE COULD LEAD TO 
PATCHY FOG DEVELOPMENT LATE. LOWS 28-34. -GIH

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
AS OF 255 AM THURSDAY...

FOR SUNDAY THROUGH MONDAY: THE MID LEVEL LOW TRACKS FROM NEAR 
CHICAGO ACROSS NORTHERN IN/OH TO PA AND OFF THE NEW ENGLAND COAST 
DURING THIS PERIOD. PASSAGE OF A REINFORCING SURFACE COLD FRONT LATE 
SUNDAY AFTERNOON WILL PULL IN EVEN CHILLIER AIR FOR SUNDAY NIGHT 
THROUGH MONDAY... AND EXPECT SLIGHTLY BELOW NORMAL HIGHS OF 46-54 
SUNDAY TO RUN WELL BELOW NORMAL MONDAY -- 43-48 -- AS THICKNESSES 
PLUMMET TO 1280-1290 M. SKIES SHOULD BE NO WORSE THAN PARTLY CLOUDY 
WITH THE NORTHWEST FLOW MOISTURE LOCKED ON THE WEST SIDE OF THE 
MOUNTAINS AND DRYING TERRAIN DOWNGLIDE OVER THE PIEDMONT. 

FOR MONDAY NIGHT THROUGH WEDNESDAY: HIGH PRESSURE CONTINUES TO BUILD 
INTO THE EASTERN US. THE POLAR LOW SITS AND SPINS OVER QUEBEC 
THROUGH TUESDAY... KEEPING A NORTHWEST MID LEVEL FLOW OVER NC... 
BEFORE THE LOW LIFTS NORTHEAST AND THE SOUTHERN STREAM ONCE AGAIN 
STARTS TO PREVAIL OVER THE TX/GULF COAST/SOUTHEAST STATES INTO 
MIDWEEK. A MID LEVEL LOW WHICH TRAVERSES SOUTHERN CA AND THE 
NORTHERN BAJA LATE MONDAY IS EXPECTED TO DAMPEN AS IT HEADS OVER 
TX/LA BY WEDNESDAY AND PICKS UP GULF MOISTURE. THE ECMWF HAS BEEN 
FAIRLY CONSISTENT IN TAKING THE SURFACE RIDGE TO OUR NORTHEAST WITH 
INCREASING SOUTHEAST FLOW INTO THE CAROLINAS AND A CHANCE OF RAIN 
VERY LATE WEDNESDAY. AS CONFIDENCE IS TYPICALLY VERY LOW IN TIMING 
FEATURES IN THIS SORT OF PATTERN THIS FAR OUT IN TIME... WILL KEEP 
THE FORECAST DRY FOR NOW. TEMPS SHOULD HOLD NEAR OR JUST UNDER 
SEASONAL NORMALS. -GIH

&&

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

24-HR TAF PERIOD:
VFR CONDITIONS ARE EXPECTED THROUGH 00Z THIS EVENING...HOWEVER... 
CEILINGS WILL BEGIN LOWERING TO MVFR/IFR BY 03-06Z...AND DOWN TO 
IFR/LIFR BY 12Z FRIDAY AS WARM ADVECTION STRENGTHENS OVER THE 
CAROLINAS IN ADVANCE OF AN APPROACHING COLD/OCCLUDED FRONT. 
KINT/KGSO TAF SITES COULD SEE PRECIPITATION BEGIN AS LIGHT FREEZING 
RAIN IN THE 06-12Z TIME PERIOD...ALTHOUGH ONLY TRACE ACCUMULATIONS 
OF ICE WOULD BE POSSIBLE BEFORE A TRANSITION TO ALL RAIN. IFR/LIFR 
CONDITIONS IN RAIN ARE EXPECTED TO MOVE INTO THE AREA FROM THE WEST 
IN THE 12-18Z TIME FRAME AS THE COLD/OCCLUDED FRONT APPROACHES AND A 
WEAK WAVE OF LOW PRESSURE DEVELOPS ALONG THE FRONT IN VICINITY OF 
CHARLOTTE...MOVING NORTHEAST ACROSS CENTRAL NC FRIDAY AFT/EVE. 
CANNOT ENTIRELY RULE OUT AN ISOLD THUNDERSTORM AT KFAY/KRWI TAF 
SITES FRIDAY AFT/EVE...HOWEVER...CHANCES FOR CONVECTION APPEAR 
MINIMAL AT THIS TIME. SURFACE WINDS WILL BE NORTHEAST ~10 KNOTS 
TONIGHT...VEERING TO THE EAST THEN TO THE SOUTHEAST DURING THE DAY 
FRI AT 10-20 KNOTS...WITH VARIABLE WINDS IN VICINITY OF THE SURFACE 
LOW. GIVEN SURFACE WINDS LIKELY IN THE 10-15 KNOT RANGE...IT IS 
UNCLEAR WHETHER OR NOT LOW LEVEL FLOW WILL BE STRONG ENOUGH TO MEET 
LOW LEVEL WIND SHEAR CRITERIA TONIGHT THROUGH FRIDAY MORNING. AT 
THIS TIME HAVE DECIDED NOT TO MENTION LLWS IN THE 18Z TAF PACKAGE... 
ALTHOUGH THIS WILL NEED TO BE REVISITED IN THE 00Z TAF PACKAGE.

FRIDAY NIGHT THROUGH MONDAY:
CEILINGS SHOULD BEGIN TO IMPROVE FROM THE WEST FRIDAY EVENING/NIGHT 
AS MID/UPPER LEVEL DRY AIR RAPIDLY FILTERS INTO THE AREA. HOWEVER... 
GIVEN THAT THE FRONT PUSHING THROUGH THE AREA WILL BE WELL-SEPARATED 
FROM THE PARENT LOW...IT MAY TAKE A WHILE FOR THE LOW LEVELS TO DRY 
OUT...AND THERE WILL BE A CHANCE FOR IFR/LIFR CEILINGS TO LINGER 
INTO/THROUGH FRIDAY NIGHT. OTHERWISE...VFR CONDITIONS ARE EXPECTED 
SAT THROUGH MON AS HIGH PRESSURE BUILDS TOWARD THE CAROLINAS FROM 
THE SOUTHWEST. -VINCENT

&&

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

&&

$$

SYNOPSIS...VINCENT
NEAR TERM...VINCENT
SHORT TERM...VINCENT/HARTFIELD
LONG TERM...HARTFIELD
AVIATION...VINCENT