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
