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FXUS62 KRAH 011645
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
1145 AM EST SUN MAR 01 2009

.SYNOPSIS...
A STRENGTHENING STORM SYSTEM OVER THE DEEP SOUTH WILL SWING EAST 
THEN NORTHEAST UP THE CAROLINA COAST THROUGH EARLY MONDAY MORNING. 
AS COLD AIR SPILLS INTO OUR REGION... WINTER STORM CONDITIONS ARE 
POSSIBLE OVER PORTIONS OF OUR REGION LATE SUNDAY INTO MONDAY.

&&

.NEAR TERM /TODAY THROUGH TONIGHT/...
AS OF 1140 AM SUNDAY...

A WINTER STORM WARNING REMAINS IN EFFECT THIS AFTERNOON THROUGH MID 
MORNING MONDAY FOR AREAS ALONG AND WEST OF HIGHWAY 1. A WINTER 
WEATHER ADVISORY REMAINS IN EFFECT FOR THE REMAINDER OF THE 
CWA EXCEPT FOR THE FAYETTEVILLE / CLINTON / GOLDSBORO AREAS FOR 
TONIGHT.

FOR TODAY: 12Z RAOB ANALYSES AND LATEST SATELLITE IMAGERY SUGGESTS 
LITTLE CHANGE IN OUR THINKING REGARDING THE UPPER AND LOWER LEVEL 
CYCLONE TRACKS AND RESULTANT TIMING AND DISTRIBUTION OF FORCING FOR 
ASCENT THROUGH TONIGHT. HOWEVER... THE TRANSITION OF PRECIPITATION 
TYPES TO SLEET AND SNOW WILL BE DELAYED FROM PREVIOUS THINKING... 
WHICH MAY YIELD A LITTLE LESS IN THE WAY OF SNOW/SLEET ACCUMULATION 
PRIOR TO SUNSET.  

THE VERY DYNAMIC UPPER LOW--CENTERED NEAR THE CENTRAL AL/GA BORDER 
AT 15Z--WILL CONTINUE TO MIGRATE NORTHEASTWARD TOWARD THE CAROLINAS 
THIS AFTERNOON. CLOUD TOPS CONTINUE TO COOL AND THE PRECIPITATION 
SHIELD CONTINUES TO EXPAND IN THE STRONGLY DIFLUENT DEFORMATION ZONE 
NORTH AND NORTHEAST OF THE UPPER LOW... AND IN THE DIVERGENT EXIT 
REGION OF 100+ KT JET NOW NOSING INTO SC. THIS STRONG LARGE SCALE 
FORCING FOR ASCENT AHEAD OF THE UPPER LOW AND JET ALOFT--IN 
CONJUNCTION WITH A STRONG AND DEEP ZONE OF FGEN (WHICH IS SUPPORTED 
BY A RATHER SHARP AND DEEP THERMAL GRADIENT OVER THE DEEP SOUTH AND 
WESTERN CAROLINAS ON 12 RAOBS)--WILL ACCORDINGLY CONTINUE TO SPREAD 
NORTHWARD AND SUPPORT INCREASING BANDED PRECIPITATION INTENSITY WITH 
TIME THIS AFTERNOON. MID LEVEL LAPSE RATES IN EXCESS OF 6 C/KM 
OVERHEAD THIS AFTERNOON COULD ALSO PRODUCE ISOLATED THUNDER JUST 
ABOUT ANYWHERE OVER CENTRAL NC. NORTHEASTERLY WINDS WILL INCREASE TO 
BETWEEN 15 AND 20 MPH WITH GUSTS 25-30 MPH BY SUNSET.

REGARDING PRECIPITATION TYPE: THE 12Z GSO SOUNDING AND RECENT AMDAR 
SOUNDINGS FROM GSO AND EVEN RDU DEPICT A SHALLOW SUB-FREEZING COLD 
NOSE... TOPPED BY A MELTING WARM NOSE ALOFT. THIS HAS SUPPORTED 
FREEZING RAIN AND SLEET MAINLY OVER THE NW PIEDMONT THIS MORNING 
(SINCE THE COLD (WARM) NOSES ARE LESS (MORE) PRONOUNCED WITH 
EASTWARD EXTENT). IN FACT... THERE WAS A FEW HOUR PERIOD OF MAINLY 
FREEZING RAIN (WITH REPORTED TEMPERATURES BETWEEN 29 AND 32 DEGREES) 
OVER THE WESTERN PIEDMONT THIS MORNING... AS THE PRECIPITATION 
INITIALLY INUNDATED CENTRAL NC. WE RECEIVED MULTIPLE REPORTS OF 
LIGHT ICING ON ELEVATED SURFACES FROM WINSTON SALEM AND GREENSBORO 
TO EFLAND... BUT ROADWAYS (INCLUDING BRIDGES AND OVERPASSES) WERE 
JUST WET. SINCE THAT TIME... SURFACE TEMPERATURES HAVE WARMED 
SLIGHTLY TO BETWEEN 32 AND 35 DEGREES WITH A REPORTED CHANGEOVER TO 
RAIN. HOWEVER... AS WE HAVE SEEN IN PAST EVENTS... ICING HAS 
APPARENTLY CONTINUED AT TREE TOP LEVEL (WHERE THE EFFECT OF THE 
WARMER GROUND IS LESS PRONOUNCED)... AND THIS HAS LED TO OVER 1000 
REPORTED POWER OUTAGES IN THE GREENSBORO AREA. GIVEN THAT THE 
CENTRAL AND WESTERN PIEDMONT WILL BE ALONG THE TRACK OF THE H85 
LOW... AND SINCE UPSTREAM SFC TEMPERATURES IN VA ARE UNIFORMLY IN 
THE LOWER 30S... LOWER LEVEL THERMAL ADVECTION SHOULD BE WEAK. 
THUS... A CHANGEOVER TO SLEET AND SNOW SHOULD BE DICTATED BY MELTING 
AND INTENSE VERTICAL MOTION-ADIABATIC COOLING/PRECIPITATION RATES 
THIS AFTERNOON. THIS MAY RESULT IN SNOW ISLANDS RATHER THAN A 
WIDESPREAD... COHERENT CHANGEOVER TO FROZEN UNTIL VERY LATE THIS 
AFTERNOON AS THE BACK EDGE OF THE MORE STRONGLY FORCED ROUND ONE OF 
PRECIPITATION DEPARTS TO THE NE. THUS... FROZEN PRECIPITATION MAY 
OCCUR INTERMITTENTLY THROUGH EARLY AFTERNOON... BUT SHOULD NOT 
BECOME PREDOMINATE UNTIL COLDER AIR ATTENDANT THE COLD POOL ALOFT 
STARTS TO MAKE INROADS IN OUR REGION LATE THIS AFTERNOON IN THE 
TRIAD AND AROUND SUNSET IN THE TRIANGLE... LEAVING PERHAPS ONLY A 
COUPLE HOUR PERIOD OF POSSIBLE FROZEN ACCUMULATION WITH ROUND ONE... 
WHICH COULD STILL YIELD A QUICK BURST OF A SLUSHY INCH OR TWO IN THE 
WESTERN PIEDMONT TO A DUSTING TO AN INCH IN THE TRIANGLE (HIGHEST 
TOWARD CHAPEL HILL). THE EXACT TIMING OF THIS CHANGEOVER AS THE BACK 
EDGE OF THE PRECIPITATION SHIELD EXITS MAKES THIS A LOW CONFIDENCE 
ACCUMULATION FORECAST FOR ROUND ONE. WE HAVE MUCH HIGHER CONFIDENCE 
IN ACCUMULATING SNOW WITH THE TRAILING DEFORMATION/COMMA HEAD/TROWAL 
PRECIPITATION BAND FORECAST TO PIVOT NORTHEASTWARD TONIGHT. -MWS

FOR TONIGHT: THE VORTEX WILL MOVE NORTHEAST THROUGH CENTRAL NC 
TONIGHT WITH COOLING THROUGH THE COLUMN TO ALL BELOW FREEZING. WE DO 
LOSE ENOUGH SATURATION WITHIN THE CRYSTAL GROWTH ZONE ALOFT THAT WE 
MAY TRANSITION TO MAINLY FREEZING DRIZZLE FOR A TIME THIS EVENING. 
AS THE 700 MB LOW SKIRTS ACROSS THE SOUTHEAST CWA SHORTLY AFTER 
MIDNIGHT... ANOTHER ROUND OF BANDED SNOWFALL IS EXPECTED ACROSS 
CENTRAL NC. PARTS OF TN HAVE RECEIVED VERY HEAVY SNOWFALL OVERNIGHT 
WITH RATES OF 1-2 INCHES PER HOUR WITHIN THE SNOW BANDS TO THE 
NORTHWEST OF THE VORTEX. BUT A COUPLE OF FACTORS MAY WORK AGAINST 
RENEWED STRONG BANDING IN NC TONIGHT... INCLUDING WANING LOW LEVEL 
FRONTOGENESIS AND ONLY MINOR MID LEVEL DEFORMATION NOTED ON BOTH THE 
NAM AND GFS... PLUS MARGINAL MOISTURE ABOVE -10C ALOFT WHICH WOULD 
LIMIT CRYSTAL GROWTH. WHEN ALL IS SAID AND DONE THOUGH... LIQUID 
PRECIP AMOUNTS ARE EXPECTED TO TOTAL AROUND 2 INCHES... AND 
FACTORING IN LOWER SNOW-LIQUID RATIOS DURING THE PERIODS OF WINTRY 
MIX... TRANSITIONING TO 10:1 TO 12:1 RATIOS AFTER THE CHANGEOVER TO 
PREDOMINANTLY SNOW... YIELDS STORM TOTAL SNOWFALL RANGING FROM LESS 
THAN ONE INCH OVER THE SOUTHEAST CWA TO 3-6 INCHES OVER MUCH OF THE 
PIEDMONT. ANY PERIOD OF FREEZING RAIN OR DRIZZLE IS EXPECTED TO 
PRODUCE ONLY NUISANCE ICING MAINLY ON ELEVATED SURFACES AND 
BRIDGE/OVERPASSES. LOW WIND CHILLS WILL PERSIST THROUGH TONIGHT AND 
GUSTS TO 35-40 MPH WILL BE POSSIBLE. EXPECT LOWS OF 25-32. -GIH

&&

.SHORT TERM /MONDAY/...
AS OF 445 AM SUNDAY...

FOR MONDAY: THE SNOW SHOULD TAPER OFF QUICKLY AS THE SURFACE LOW 
ZIPS UP OFF THE NORTHEAST COAST AND LOW LEVEL WINDS BECOME NNWRLY. 
LITTLE ADDITIONAL ACCUMULATION IS EXPECTED MONDAY MORNING. EXPECT 
SKIES TO PARTIALLY CLEAR FROM SW TO NE... ALTHOUGH WITH EXPECTED 
DAMP OR SNOWY GROUND... HIGHS SHOULD ONLY REACH 32-36... AND EVEN 
THIS MAY BE GENEROUS. WINDS WILL TAPER DOWN QUICKLY DURING THE 
AFTERNOON. -GIH

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
AS OF 355 AM SUNDAY...

MAIN CHANGE TO THE LONG TERM WAS TO ADJUST TEMPS DOWNWARD MONDAY 
NIGHT AND TUESDAY IN ANTICIPATION OF SNOW COVERAGE. ARCTIC HIGH OVER 
THE GREAT LAKES WILL BUILD/DROP SEWD TOWARD CENTRAL NC MON NIGHT AND 
TUESDAY. WHILE NOT EXPECTING NEAR SURFACE LAYER TO DECOUPLE...STILL 
EXPECT VERY COLD MIN TEMPS BY TUESDAY MORNING DUE TO THE ABNORMALLY 
COLD AIR ASSOCIATED WITH THE HIGH. MODEL THICKNESSES IN THE 1240S 
HISTORICALLY SUPPORT MIN TEMPS CLUSTERING AROUND 11-12 DEGREES 
ABOVE. MOS GUIDANCE TRENDING COOLER SO HAVE ADJUSTED MIN TEMPS 
SIMILAR TO HISTORICAL VALUES (NEAR 12 DEGREES NW TO 17/18 DEGREES 
FAR SE. SURFACE HIGH SETTLES OVER REGION BY LATE IN THE DAY. FULL 
SUN THICKNESSES SUGGEST MAX TEMPS IN THE MID/UPPER 30S. ACCOUNTING 
FOR EARLY MARCH SUN ANGLE AND WINDS BECOMING LIGHT...EXPECT MAX 
TEMPS TO RANGE UPPER 30S IN THE NW TO THE LOWER/MID 40S SOUTH. 
DEPENDING UPON DEPTH OF SNOW PACK...MAX TEMPS TUESDAY MAY END UP 
BEING A FEW DEGREES COOLER.

WEDNESDAY THROUGH SATURDAY WILL SEE A WARMING TREND AS L/W TROUGH 
LIFTS NE AND UPPER LEVEL FLOW BACKS WESTERLY. TEMPS SHOULD RETURN TO 
NEAR NORMAL LEVELS THU WITH ABOVE NORMAL VALUES EXPECTED FRI AS LOW 
LEVEL FLOW BECOMES SW IN RESPONSE TO SURFACE RIDGE DRIFTING OFFSHORE 
AND A COLD FRONT ADVANCING EAST ACROSS THE MID MS VALLEY AND LOWER 
OH VALLEY. EXPECT TO SEE AN INCREASE IN CLOUDINESS AS WARM AIR 
ADVECTION PATTERN WILL ALSO INCREASE MOISTURE ACROSS THE REGION. 
HOWEVER FRI INTO SATURDAY PERIOD STILL APPEARS TO BE DRY AS BEST 
FORCING FOR PRECIP REMAINS TO OUR NW. ABOVE NORMAL TEMPS EXPECTED ON 
SATURDAY...IN THE UPPER 60S TO NEAR 70. DEPENDING UPON CLOUD 
COVERAGE...MAX TEMPS SATURDAY COULD EASILY BE IN THE LOW/MID 70S.-WSS

&&

.AVIATION /12Z SUNDAY THROUGH THURSDAY/...
AS OF 740 AM SUNDAY...

IFR/LIFR CONDITIONS EXPECTED THROUGH THE TAF FORECAST PERIOD.

WIDESPREAD PRECIPITATION IS CURRENTLY MOVING INTO CENTRAL NORTH 
CAROLINA THIS MORNING... IN RESPONSE TO INTENSE LIFT AHEAD OF A 
VIGOROUS UPPER LEVEL LOW. SOME ELEVATED CONVECTION HAS MOVED INTO 
WITH THIS AREA OF PRECIP. DO NOT EXPECT TO SEE MANY EMBEDDED 
THUNDERSTORMS THIS MORNING. HOWEVER... WILL INCLUDE A MENTION OF CB 
AT KRDU... KFAY... AND KRWI FOR THIS MORNING... AND ADD THUNDER IF 
NECESSARY. AS COLDER AIR SPILLS INTO CENTRAL NORTH CAROLINA LATE 
THIS MORNING THROUGH INTO THE AFTERNOON... THE PRECIPITATION LIKELY 
WILL TRANSITION TO A WINTRY MIX.... MAINLY FROM RDU WESTWARD. A 
TRANSITION TO ALL SNOW IS EXPECTED TO ACROSS INT/GSO/RDU TERMINALS 
LATE THIS MORNING INTO THIS AFTERNOON. THE SNOW HAS THE POTENTIAL TO 
BECOME HEAVY AT TIMES OVER INT/GSO SUNDAY AFTERNOON AND EVENING 
WHICH COULD POSE SIGNIFICANT AVIATION IMPACTS. 

FARTHER EAST AND SOUTH AT KRWI/KFAY... IN THE FORM OF RAIN AND OR 
DRIZZLE BEFORE TRANSITIONING TO A BRIEF PERIOD OF LIGHT SNOW AT 
AROUND 04Z TO 05Z...BUT THE BEST LIFT AND MOISTURE APPEARS TO STAY 
NORTH AND WEST OF THESE TERMINALS. THUS... IFR/LIFR CIGS SHOULD 
CONTINUE THROUGH SUNDAY... WITH LIFR VISIBILITIES POSSIBLE AS THE 
PRECIPITATION CHANGES TO SNOW. 

IN ADDITION TO THE WINTRY PRECIP...WINDS WILL BE STRONG OUT OF THE 
NNE AT AROUND 15 KTS SUSTAINED WITH OCCASIONALLY GUSTS MIDDAY SUNDAY 
INTO SUNDAY NIGHT UPWARD OF 25 TO 30 KTS. WHILE THE LOW LEVELS MAY 
REMAIN WELL-MIXED... LLWS COULD BE A THREAT TONIGHT... AS A STRONG 
40-50 KT NORTHEASTERLY LOW LEVEL JET AT 2000 FT DEVELOPS OVERHEAD. 
HAVE INCLUDED A LLWS AT ALL TAF SITES GENERALLY BETWEEN 00Z AND 
06Z... AS WINDS ALOFT LOOK TO BE THE STRONGEST THEN... AND MEET 
CRITERIA.

VFR CONDITIONS MAKE A RETURN FROM WEST TO EAST VERY MONDAY... AND 
WILL PERSIST INTO THURSDAY.

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WARNING FROM NOON TODAY TO 9 AM EST MONDAY FOR 
NCZ007>010-021>026-038>041-073>076-083-084.
WINTER WEATHER ADVISORY FROM 6 PM THIS EVENING TO 9 AM EST 
MONDAY FOR NCZ011-027-028-042-043-077-085-086.

&&

1132

SYNOPSIS...MWS/HARTFIELD
NEAR TERM...HARTFIELD
SHORT TERM...HARTFIELD
LONG TERM...WSS
AVIATION...BSD