FXUS62 KRAH 242354
AFDRAH
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
654 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 BY LATE TONIGHT THROUGH CHRISTMAS NIGHT. DRIER AIR
WILL RETURN SATURDAY THROUGH MONDAY... AS COOL HIGH PRESSURE BUILDS
IN FROM THE NORTHWEST.
&&
.NEAR TERM /THROUGH FRIDAY/...
AS OF 559 PM PM THURSDAY...
WE WILL GO AHEAD AN ISSUE A FREEZING RAIN ADVISORY FOR THE I-40/85
CORRIDOR FROM WINSTON-SALEM THROUGH GREENSBORO... BURLINGTON...
HILLSBOROUGH... AND ROXBORO FROM 400 AM THROUGH 900 AM FRIDAY. THE
HIGH TO THE NORTH IS STRONG ENOUGH (1030+ MB) TO CONTINUE TO
DELIVER CAA INTO OUR NW PIEDMONT THROUGH THE EARLY MORNING HOURS.
THIS CAA WILL CONTINUE TO BE OVER THE DEEP SNOW COVER (4+ INCHES) OVER
VA AND NW NC. THE HIGH RAPIDLY RETREATS FRIDAY MORNING. HOWEVER...
THE RAPID DEVELOPMENT OF WAA PRECIPITATION IS EXPECTED BETWEEN
09Z-12Z IN THE WESTERN PIEDMONT... WHICH MAY REACH THE ROXBORO
AREA BEFORE 12Z. THE NAM AND RUC BOTH INDICATE SURFACE WET BULBS
OF BETWEEN 30-32 FROM 09Z-13Z... BEFORE RISING TO 32 OR ABOVE BY
13-15Z. THE TIMING OF THE CHANGEOVER TO RAIN WILL BE SLOWEST IN
THE FAR NW. STILL... SOME TRACE TO 1/10 INCH OF FREEZING RAIN CAN
BE EXPECTED ON EXPOSED SURFACES BEFORE THE WARMER AND HEAVIER RAINS
BEGIN AT MID MORNING. -BADGETT
PREVIOUS DISCUSSION ISSUED AT 200 PM FRIDAY...
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
AIR MASS 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 WET BULB 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 NIGHT THROUGH SUNDAY NIGHT/...
AS OF 310 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 THROUGH SUNDAY NIGHT
THE MAJORITY OF MODELS HAVE A SURFACE TROUGH LINE FROM BURLINGTON
TO LUMBERTON AT SUNSET FRIDAY AND QUICKLY SHIFT THIS FEATURE EAST...
OUT OF CENTRAL NORTH CAROLINA AROUND MIDNIGHT. WITH UPPER LEVEL
DYNAMICS WELL EAST OF THE SURFACE TROUGH FRIDAY NIGHT... RAIN SHOULD
END AS THE SURFACE TROUGH PASSES. RAIN IN THE WEST WILL END FRIDAY
EVENING AND IN THE EAST AROUND MIDNIGHT. THE REMAINDER OF THIS
FORECAST PERIOD WILL BE DRY.
WEAK SURFACE HIGH PRESSURE TO THE SOUTH WILL BE IN CONTROL OF THE
WEATHER SATURDAY INTO SUNDAY NIGHT. PARTLY CLOUDY SKIES ARE
EXPECTED.
COLD AIR TO RUSH IN BEHIND THE EXITING FRONT ON FRIDAY NIGHT.
THICKNESS GRADIENT AND ELEVATION SUGGEST AT LEAST A TWELVE DEGREE
SPREAD. MID 30S NORTHWEST TO UPPER 40S EXTREME EAST. PLEASANT
AFTERNOON TEMPERATURES WITH MID 50S NORTHWEST TO LOWER 60 SOUTHEAST
SATURDAY THEN NEAR 50 TO MID 50S SUNDAY. LOW TEMPERATURES SATURDAY
NIGHT IN THE 30 TO 35 DEGREE RANGE.
&&
.LONG TERM /MONDAY THROUGH THURSDAY/...
AS OF 310 PM...
RESPECTABLE UPPER WAVE APPROACHING THE APPALACHIAN MOUNTAINS AT
SUNRISE MONDAY. WITH NORTHWEST TO WEST FLOW AT THE SURFACE AND NO
LOW LEVEL DYNAMICS... CENTRAL NORTH CAROLINA SHOULD BE DRY. SURFACE
HIGH PRESSURE SETTLES OVER NORTH CAROLINA BY TUESDAY EVENING AS
UPPER LEVEL RIDGING APPROACHES NORTH CAROLINA FROM THE WEST. THE 12Z
ECMWF MODEL HAS SIGNIFICANTLY DEEPENED A MIDWEST UPPER TROUGH FOR
WEDNESDAY MORNING... AND IS THEREFORE MUCH MORE AGGRESSIVE IN
LIFTING MOISTURE INTO NORTH CAROLINA WEDNESDAY NIGHT. THIS SCENARIO
IS REJECTED FOR LACK OF SUPPORT FROM OTHER MODELS... WHICH ARE MUCH
MORE ZONAL IN THEIR UPPER LEVEL FLOW. NO SIGNIFICANT PRECIPITATION
CHANCES DURING THIS FORECAST PERIOD.
LOW LEVEL THICKNESSES BELOW NORMAL FOR THE PERIOD AND THIS IS
REFLECTED IN SLIGHTLY BELOW NORMAL TEMPERATURES. AFTERNOON HIGH
TEMPERATURES ROUGHLY MID 40S TO LOWER 50S THROUGH THE PERIOD.
OVERNIGHT LOW TEMPERATURES MID 20S TO LOWER 30S.
&&
.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
AS OF 645 PM THURSDAY...
CEILINGS WILL LOWER 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 DURING THE
09-14Z 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 JUST SOUTH OF THE REGION ALONG THE APPROACHING
FRONT. THIS LOW IS EXPECTED TO MOVE NORTHEAST ACROSS CENTRAL NORTH
CAROLINA THROUGH FRIDAY AFTERNOON/EVENING. THERE WILL ALSO BE A
SLIGHT CHANCE OF AN ISOLATED THUNDERSTORM AT THE KFAY/KRWI TAF SITES
FRIDAY AFTERNOON/EVENING. HOWEVER...CHANCES FOR CONVECTION APPEAR
MINIMAL AT THIS TIME AND THEREFORE WILL LEAVE ANY MENTION OF TSRA
OUT OF THE TAFS. SURFACE WINDS WILL GENERALLY BE NORTHEAST AROUND 10
KNOTS OVERNIGHT AND WILL GRADUALLY VEER TO THE EAST AND EVENTUALLY
TO THE SOUTHEAST DURING THE DAY FRIDAY...AS WELL AS INCREASE TO NEAR
15-20 KNOTS. A STRONG LOW LEVEL JET WILL BE IN PLACE OVERHEAD (35 TO
45 KNOTS)...HOWEVER WITH WINDS AT THE SURFACE LIKELY IN THE 15-20
KNOT RANGE...LOW LEVEL WIND SHEAR WILL BE MARGINAL. FOR NOW...HAVE
DECIDED NOT TO INCLUDE LLWS IN THE TAFS...HOWEVER THIS WILL HAVE TO
BE MONITORED CLOSELY. -KRR
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...
FREEZING RAIN ADVISORY FROM 4 AM TO 9 AM EST FRIDAY FOR NCZ007-
021>024.
&&
$$
SYNOPSIS...VINCENT/BADGETT
NEAR TERM...BADGETT/VINCENT
SHORT TERM...VINCENT
LONG TERM...RWH
AVIATION...KRR/VINCENT
