FXUS62 KRAH 181533
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
1033 AM EST THU JAN 18 2007

.SHORT TERM /REST OF TODAY/...
12Z UPPER AIR ANALYSIS REVEALED TWO FEATURES THAT WILL [LAY MAJOR
ROLES IN P-TYPE THIS AFTERNOON. FIRST, DRIER AIR NOTED UPSTREAM
OF CENTRAL NC IN THE 700-500MB LAYER. THIS LAYER COINCIDES
IN FAVORED DENDRITE REGION. WITH MOISTURE DECREASING...EXPECT
SNOW TO DIMINISH NEXT FEW HOURS. ALSO NOTED WAS STRONG FETCH OF
WARMER AIR AROUND 850MB UPSTREAM. THIS WARM AIR SURGE ALSO NOTED
IN AIRCRAFT SOUNDINGS FROM CLT AND AREA VAD WIND PROFILES FROM
ACROSS AREA. THUS EXPECT PATCHES OF SNOW OVER THE NW PIEDMONT TO
TRANSITION TO FREEZING RAIN NEXT COUPLE HOURS WITH MAINLY LIGHT
PRECIP EXPECTED THROUGH THE AFTERNOON. DO NOT EXPECT THE TRIAD
REGION TO WARM TO AROUND FREEZING UNTIL LATE IN THE DAY. THE
PERSISTENT FREEZING PRECIP WILL LIKELY RESULT IN ICE ACCUMULATION
OF A TENTH OF AN INCH.

IN THE NE PIEDMONT...WIDESPREAD FREEZING RAIN WILL TRANSITION TO
RAIN AS SURFACE TEMPS RISE TO AROUND FREEZING WITH MUCH WARMER AIR
ALOFT. WILL MAINTAIN CATEGORICAL POPS FOR NOW. EXPECT PRECIP TO
DIMINISH SW-NE LATE TODAY AND EARLY TONIGHT.

FINALLY...ADJUSTED MAX TEMPS DOWN A DEGREE OR TWO...MAINLY IN THE
NORTHERN PIEDMONT.

&&

.PREV DISCUSSION...
/ISSUED 617 AM EST THU JAN 18 2007/ 

SHORT TERM /REST OF TODAY THROUGH SATURDAY NIGHT/...
THE WINTER WEATHER ADVISORY HAS BEEN EXPANDED TO INCLUDE THE
NORTHERN COASTAL PLAIN UNTIL NOON TODAY.

PREV DISCUSSION...
/ISSUED 412 AM EST THU JAN 18 2007/ 

CORRECTION TO WSW ENDING TIME NW PIEDMONT.
RFG

PREV DISCUSSION...
/ISSUED 339 AM EST THU JAN 18 2007/ 

UPDATE...
RADAR ECHOES ARE RAPIDLY SPREADING ACROSS CENTRAL NC. MOST PCPN
REMAINS ALOFT...BUT SOME IN THE FORM OF SNOW HAS BEEN REPORTED IN
THE SOUTHERN TIER COUNTIES. ADVISORIES HAVE REVERTED TO THEIR
EARLIER START TIMES OF 4 AM ACROSS THE SOUTH AND 6 AM ACROSS THE
NORTH TO MAKE PEOPLE AWARE THAT PCPN IS BEGINNING TO REACH THE
GROUND AS EARLIER PREDICTED. -RFG

PREV DISCUSSION...
/ISSUED 220 AM EST THU JAN 18 2007/ 

SHORT TERM /TODAY THROUGH SATURDAY NIGHT/...
TODAY...STRONG JET ALOFT WITH 160+ KTS OUT OF THE RED RIVER VALLEY 
TOWARD NC IS HELPING TO DRAW WARMER MOIST AIR ALOFT FROM THE GULF 
STATES TOWARD THE CAROLINAS.  RADAR SHOWS DEVELOPING PCPN AREAS FROM 
ALABAMA EASTWARD WITH JUST A SLIGHT NORTHWARD PROGRESSION. MOIST 
SOUTHERLY FLOW ALOFT IS ENCOUNTERING AND BEGINNING TO OVERRUN MUCH 
DRIER AIR OVER CENTRAL NC AND MOST PCPN IS LIKELY TO EVAP/SUBLIMATE 
FOR SEVERAL HOURS BEFORE THE COLUMN SATURATES OVER THIS AREA.  

CURRENT ALIGNMENT OF WINTER WEATHER ADVISORIES WILL BE KEPT IN PLACE 
ACROSS CENTRAL NC...BUT ONSET DELAYED A COUPLE HOURS...AND POSSIBLY 
ENDING EARLIER.  AREAS OF PCPN IN THE FORM OF SLEET OR FRZG 
RAIN SHOULD START IN THE SRN TIER TOWARD DAYBREAK...WITH MEASURABLE 
PCPN AS FAR NORTH AS HIGHWAY 64 BY 10 AM AND AS FAR NORTH AS THE VA 
BORDER AROUND NOON.

MODEL THICKNESS VALUES ARE SHOWING A MORE RAPID WARMUP DURING THE 
DAY MEANING A QUICKER TRANSITION FROM SLEET TO FRZG RAIN TO RAIN. 
DRYNESS IN THE DENDRITE GROWTH ZONE ALOFT SUGGESTS NEGLIGIBLE 
CHANCES OF SNOW.  PROGNOSES OF SURFACE WET BULB TEMPERATURES SHOWS 
THE THREAT OF FREEZING RAIN RETREATING WEST OF U.S. ROUTE 1 BY 10 AM 
AND LIMITED TO THE TRIAD AROUND NOON...ABOVE FREEZING THROUGHOUT THE 
CWA AFTER 1 PM.

GIVEN THE TIGHT GRADIENT WESTERLY FLOW ALOFT...THERE IS LITTLE 
OPPORTUNITY FOR WAVE AMPLIFICATION...EFFECTIVELY CUTTING OFF THE 
NORTHWARD SURGE OF WARM MOIST AIR.  THIS SHOULD MEAN RAPIDLY 
DECREASING QPF NORTHWARD OVER THE NRN TIER OF CENTRAL NC. EXPECT QPF 
OF .25-.50 IN THE SOUTHEAST THIRD TAPERING TO ONLY A FEW HUNDREDTHS 
OF AN INCH IN THE NORTHERN TIER OF COUNTIES.  MAX TEMPERATURES NEAR 
34 IN THE TRIAD TO 43 IN SAMPSON CO.  

TNGT..THE THREAT OF RAIN CONTINUES IN THE EASTERN HALF UNTIL AROUND 
MIDNIGHT WITH SKIES REMAINING CLOUDY THROUGHOUT OVERNIGHT.  THE RAIN 
COOLED PIEDMONT AIRMASS SHOULD LINGER INTO FRI.  LOWS OF 30 NW TO 37 
SE MEANS SOME ICY PATCHES IN THE NW THIRD ARE POSSIBLE EARLY FRI. 
-RFG

FRIDAY AND FRIDAY NIGHT...THE SFC CYCLONE WILL CONTINUE TO DEPART 
THE REGION AS IT HEADS FURTHER NORTHEAST. THIS WILL LEAVE THE CWA IN 
DRY NORTHWEST FLOW BOTH AT THE SFC AND ALOFT. FORECAST SOUNDINGS 
INDICATE THAT MIXING SHOULD OCCUR TO NEAR 850 MB WHERE WINDS OF 40 
TO 45 KTS WILL BE PRESENT. MEANWHILE...THE SFC PRESSURE GRADIENT 
TIGHTENS OVER CENTRAL NORTH CAROLINA AS THE ATLANTIC LOW DEEPENS AND 
HIGH PRESSURE MOVES INTO THE CENTRAL U.S. THESE FACTORS WILL RESULT 
IN BREEZY CONDITIONS WITH WINDS POSSIBLY GUSTING TO 25 TO 30 MPH 
DURING THE AFTERNOON. TEMPERATURES WILL ALSO CONTINUE TO BE ON THE 
COOL SIDE AS LOW LEVEL THICKNESSES INDICATE HIGHS IN THE MID TO 
UPPER 40S...WHICH ARE LOWER THAN THE CONSENSUS MOS. LOWS FRIDAY 
NIGHT WILL DIP INTO THE MID 20S TO NEAR 30.

SATURDAY AND SATURDAY NIGHT...COOL DRY NORTHWEST FLOW WILL PERSIST 
ACROSS THE FORECAST AREA. A REINFORCING SHOT OF COOLER AIR FILTERS 
INTO THE AREA ON SATURDAY AFTERNOON...EVIDENT BY 850MB TEMPS 
DROPPING TO AROUND -8C. HIGHS ARE ONCE AGAIN EXPECTED TO BE BELOW 
MOS GUIDANCE...FROM AROUND 40 IN THE NE PIEDMONT TO MID 40S IN THE 
COASTAL PLAIN. LOW LEVEL THICKNESS TECHNIQUE SUGGESTS IT MAY BE EVEN 
COOLER THAN THIS...SO WILL CONTINUE TO MONITOR. 

SFC HIGH PRESSURE SETTLES OVER CENTRAL NC BY SUNDAY MORNING. LIGHT 
WINDS AND LOW DEWPOINTS POINT TO A VERY CHILLY NIGHT...BUT 
INCREASING MID TO HIGH LEVEL CLOUDS WILL LIKELY HOLD TEMPS UP 
SOMEWHAT. TEMPS STILL EXPECTED TO DROP INTO THE 20S.   -JFB

LONG TERM /SUNDAY THROUGH WEDNESDAY/...
NOT A LOT OF CONFIDENCE IN THE TIMING OF THE EVENT LATE THIS WEEKEND 
AS MODEL EVOLUTION WAS FAST LAST NIGHT...AND HAS SPED UP EVEN 
MORE TONIGHT. LOW PRESSURE RACES ACROSS THE SOUTHERN STATES AND THE 
TRANSITORY COLD HIGH WILL BE REINFORCED AS PRECIP OVERSPREADS THE 
AREA SUNDAY AFTERNOON/EVENING. WARM AIR ASSOCIATED WITH THE 
OVERRUNNING WILL BE STRONG WITH A 50KT LLJ...THUS MIXED PRECIP IS A 
FAIR BET AS EVAPORATIVE COOLING COULD EASILY LOCK TEMPS IN 
THE CLIMATOLOGICALLY FAVORED AREA IN THE 30S ALL DAY. THERMAL 
STRUCTURE AND TIMING OF THE ONSET IS STILL QUITE UNCERTAIN...WILL 
ONLY MENTION R/S FOR NOW UNTIL THE TIMING MATTER IS RESOLVED. 
OTHERWISE...WILL BE ENDING THE PRECIP A LITTLE EARLIER AS ON 
MONDAY...OTHERWISE NO CHANGES TO THE LATER EXTENDED. -MM

AVIATION /06Z-06Z/...
VFR CONDS EARLY IN THE TAF PERIOD WILL GIVE WAY TO MVFR/IFR CIGS AND 
VIS FOR THE REMAINDER OF THE TAF PERIOD AS PRECIP DEVELOPS AND 
ADVECTS INTO THE CWA FROM THE SOUTH BETWEEN 10-13Z THIS MORNING. 
PRECIP IS EXPECTED TO BEGIN AS SNOW AT GSO...TRANSITIONING TO SN/PL 
AND EVENTUALLY FZRA BY 18Z. FZRA AND EVENTUALLY RAIN ARE EXPECTED 
FOR THE REMAINDER OF THE TAF PERIOD AT GSO. AT RDU/FAY...PRECIP IS 
MORE APT TO BEGIN AS FZRA BEFORE TRANSITIONING TO RAIN BY 
15-18Z...ALTHOUGH A BRIEF PERIOD OF SN/PL CANNOT BE RULED OUT AT 
ONSET. AT RWI...PRECIP WILL LIKELY FALL AS RAIN WITH THE EXCEPTION 
OF A BRIEF PERIOD OF FZRA AT ONSET. PRECIP ASSOC/W THE WEAK COASTAL 
LOW WILL END FROM SOUTHWEST TO NORTHEAST NEAR THE END OF THE TAF 
PERIOD. -VINCENT/MM

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY UNTIL NOON EST TODAY FOR NCZ008>011-
025>028-040-041-043-073>076-083-084.

WINTER WEATHER ADVISORY UNTIL 4 PM EST THIS AFTERNOON FOR 
NCZ007-021>024-038-039.

&&

$$