FXUS62 KRAH 250611
AFDRAH
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
110 AM EST FRI DEC 25 2009
.SYNOPSIS...
A STORM SYSTEM TO OUR SOUTHWEST WILL MOVE NORTHEAST AND AFFECT THE
REGION THROUGH CHRISTMAS DAY AND THROUGH THE EVENING... SLOWLY
EXITING TO OUR NORTHEAST SATURDAY MORNING. A DRY HIGH PRESSURE AREA
WILL BUILD IN OVER THE WEEKEND... THEN A SECONDARY COLD FRONT WILL
BRING COOLER TEMPERATURES FOR MONDAY THROUGH TUESDAY.
&&
.NEAR TERM /THROUGH FRIDAY/...
AS OF 945 PM THURSDAY...
A FEW CONCERNS THIS EVENING. 1) THE THREAT OF LIGHT FREEZING RAIN
EXISTS OVER THE NORTHWEST INTO NORTH CENTRAL PIEDMONT OF NC...
ROUGHLY ALONG AND NORTH OF THE 1-40/85 CORRIDOR FROM WINSTON-SALEM
AND GREENSBORO TO BURLINGTON TO HILLSBOROUGH AND ROXBORO. THE MAIN
THREAT PERIOD APPEARS TO BE BETWEEN 09Z AND 14Z. HOWEVER... DUE TO
THE RAIN DEVELOPING ALREADY ACROSS AREAS ALONG AND WEST OF
HICKORY... WE MAY BEGIN TO GET SOME LIGHT FREEZING RAIN A FEW HOURS
BEFORE THIS.
THE FREEZING RAIN IS SUPPORTED BY THE P-TYPE NOMOGRAM PARTIALS THAT
FORECAST LOW AND MID LEVEL THICKNESSES IN THE 1305-1310M/1560-1570M
RANGE BY 12Z FRIDAY IN THIS AREA. THIS GIVES FREEZING RAIN OR RAIN
WITH THE EMPHASIS ON FREEZING RAIN WHERE THE SURFACE WET BULB
FORECASTS ARE 31.9 OR LOWER. THE LATEST NAM/RUC FORECASTS CONTINUE
TO INDICATE 30-32 SURFACE WET BULB FORECASTS FROM WINSTON-SALEM AND
GREENSBORO TO ROXBORO FROM 06Z-12Z... RAPIDLY INCREASING TO 35-40
BETWEEN 15Z-18Z. THIS OCCURS AS A STRONG WARM INTRUSION ALOFT SURGES
OVERHEAD. QPF BY 12Z COULD NEAR OR REACH 0.25 IN THE ADVISORY
AREA... BUT ONLY 0.01 TO 0.10 OR SO SHOULD ACTUALLY FREEZE ON IMPACT
AS ICE ESPECIALLY ON ELEVATED SURFACES. ADDITIONAL ADDED SUPPORT FOR
SOME FREEZING RAIN TOWARD DAYBREAK IS THAT THE PARENT HIGH TO THE
NORTH WAS DELIVERING GOOD CAA INTO THE PIEDMONT THIS EVENING (DEW
POINTS IN VA WERE IN THE TEENS WITH TEMPS IN THE 20S). THE HIGH WILL
BE RETREATING BY AROUND DAYBREAK... BUT WILL STILL HAVE DELIVERED
COLD DRY AIR INTO THE PIEDMONT SUPPORTING SURFACE WET BULBS 31.9 OR
BELOW BY 12Z.
OVERALL... WE EXPECT THIS TO BE A NUISANCE EVENT DUE TO THE
TRANSITORY COLD HIGH... STRONG WARMING ALOFT (MUCH MORE THAN THE
DECEMBER 18 STORM... AND THE HEAVY RAINFALL RATES. THEREFORE...
MOST ICING SHOULD BE CONFINED TO THE ELEVATED SURFACES EARLY ON WHEN
IT WILL BE COLDEST AND WHEN THE PRECIPITATION RATES ARE LIGHTER.
THERE COULD BE SOME SLICK SPOTS... ESPECIALLY ON BRIDGES AND
OVERPASSES IN THE ADVISORY AREA. ADVISORIES ARE ISSUED WHEN ANY
ACCUMULATION OF ICE IS EXPECTED.
TO THE SOUTH AND EAST OF THE ADVISORY AREA... WE EXPECT RAIN TO
DEVELOP FROM THE SW OVERNIGHT. LOWS IN THE MID TO UPPER 30S ARE
EXPECTED.
2) THE SECOND CONCERN TONIGHT IS THE SLIGHT RISK OF SEVERE
THUNDERSTORMS FRIDAY AFTERNOON OVER OUR FAR SE COASTAL PLAIN
COUNTIES. A TRIPLE POINT LOW IS EXPECTED TO TRACK NE FROM SC ACROSS
THE COASTAL PLAIN FRIDAY AFTERNOON AND EARLY EVENING. A FORCED LINE
OF SHOWERS AND ISOLATED THUNDERSTORMS SHOULD TRACK ALONG THE COLD
FRONT AS IT PUSHES THROUGH THE COASTAL PLAIN FRIDAY AFTERNOON.
MODELS DO INDICATE SURFACE DEW POINTS MAY APPROACH 60 FROM
FAYETTEVILLE TO GOLDSBORO BETWEEN 18Z-22Z. HIGHS SHOULD SOAR INTO
THE LOWER 60S IN THIS REGION. A NEGATIVELY TILED UPPER TROUGH
APPROACHING COMBINED WITH A TRIPLE POINT LOW DEVELOPMENT OVER OUR SE
ZONES SHOULD ALLOW FOR THE BAND OF CONVECTION TO REMAIN ORGANIZED AS
IT MOVES THROUGH THE COASTAL PLAIN AND COASTAL AREA. THE BACKED LOW
LEVEL WINDS ALONG THE WEDGE BOUNDARY MAY PRODUCE WIND PROFILES
SUPPORTIVE OF ROTATING STORMS AND POSSIBLY A SUPERCELL OR TWO. THE
MAIN THREAT APPEARS THAT IT WOULD REMAIN JUST SE OF FAY TO GSB...
BUT WE WILL HAVE TO MONITOR CLOSELY. FOR NOW... WE WILL MENTION THE
SLIGHT RISK OF SEVERE FOR THE SE ZONES DURING THE AFTERNOON.
3) FLOODING POTENTIAL
FOR NOW... IT APPEARS THAT THE THREAT OF FLASH FLOODING WILL BE LOW.
HOWEVER... WITH A QPF IN THE 1 TO 2 INCH RANGE... AND MOSTLY IN 6
HOURS TIME... THERE WILL LIKELY BE SOME MINOR RUNOFF PROBLEMS. THE
SNOW COVER REMAINS OVER FORSYTH... NW GUILFORD... AND PERSON
COUNTIES WHERE SOME LOCAL STILL HAD 3-4 INCHES ON THE GROUND. THIS
QPF ON TOP OF THE MELTING SNOW FRIDAY AFTERNOON SUGGEST AT LEAST
MINOR RUNOFF CONCERNS. WE WILL NOT ISSUE A FLASH FLOOD WATCH AT THIS
TIME SINCE THE FLOODING ISSUES SHOULD REMAIN MINOR. THIS IS
SUPPORTED BY THE 3-6 HOUR FLASH FLOOD GUIDANCE OF 2.3 TO 2.4 INCHES
OVER THE FORSYTH/PERSON ZONES. WE WILL HIGHLIGHT THIS THREAT IN THE
HAZARDOUS WEATHER OUTLOOK.
-BADGETT
PREVIOUS DISCUSSION ISSUED 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
&&
.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 /06Z FRIDAY THROUGH TUESDAY/...
AS OF 110 AM FRIDAY...
CEILINGS WILL LOWER TO IFR/LIFR BY 12Z THIS MORNING AS WARM
ADVECTION STRENGTHENS AND PRECIPITATION SPREADS NORTH OVER THE
CAROLINAS IN ADVANCE OF AN APPROACHING COLD 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 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 THIS AFTERNOON/EVENING. 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...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. -KRR
SATURDAY THROUGH MONDAY:
VFR CONDITIONS ARE EXPECTED TO RETURN BY SAT AND LAST THROUGH MON
AS HIGH PRESSURE BUILDS TOWARD THE CAROLINAS FROM THE SOUTHWEST.
&&
.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
SHORT TERM...VINCENT
LONG TERM...RWH
AVIATION...KRR/SMITH
