FXUS62 KRAH 261137
AFDRAH
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
635 AM EST SAT DEC 26 2009
.SYNOPSIS...
A COLD FRONT WILL PUSH EAST AND OFF THE COAST EARLY THIS MORNING.
WEAK HIGH PRESSURE WILL BUILD INTO NC FROM THE GULF COAST STATES
SATURDAY THROUGH SUNDAY.
&&
.NEAR TERM /THROUGH SUNDAY NIGHT/...
AS OF 300 AM SATURDAY...
COMPLEX SFC PATTERN THIS MORNING ACROSS THE MID ATLANTIC AND
CAROLINAS. A WEAK SFC LOW WAS MOVING NE ACROSS THE COASTAL PLAIN
WITH DEW POINTS AT OR ABOVE 60 DEG ACROSS THE COASTAL PLAIN AND
COASTAL REGION. BEHIND THE SFC WAVE...DEW POINTS DROP NOTICEABLY
INTO THE UPPER 30S TO MID 40S (KRDU DROPPED FROM 56 DEG AT 04Z TO 45
DEG AT 07Z WITH SIMILAR DROPS AT KHNZ AND KTTA.) THE EASTWARD
PROGRESSION OF THE LOW LEVEL DRY AIR WAS WILL HANDLED BY LOCAL 12KM
WRF GUIDANCE WHICH PROGS SFC DEW POINTS AT OR BELOW 45 DEG BY 12Z
SAT. EVEN WITH THE DRYING AT THE SFC...THE PERSISTENT LOW CLOUDS
WILL CONTINUE INTO THE POST DAYBREAK HOURS AS SATURATED CONDITIONS
ARE PROGGED TO CONTINUE BASED ON LATEST BUFR SOUNDING DATA. FOG IS
STILL REPORTED AT MOST LOCATIONS BUT VSBYS IMPROVED INTO THE 1-3SM
RANGE DURING THE PAST SEVERAL HOURS.
TODAY...NWP GUIDANCE MOVES THE SFC WAVE INTO THE LOWER CHESAPEAKE
BAY THIS AFTERNOON WITH A WEAK AREA OF HIGH PRESSURE BUILDING INTO
THE REGION FROM THE NORTHERN GULF COAST. SFC WINDS WILL BECOME LIGHT
FROM THE W TODAY ALLOWING THE LOW LEVELS TO DY OUT. MODEL BUFR
SOUNDINGS INDICATED SOME MOISTURE WILL PERSIST INTO MIDDAY BELOW A
SUBSIDENCE INVERSION RESULTING IN SCT-BKN CLOUDS AROUND 2K FEET
THROUGH EARLY THIS AFTERNOON. AS LOW LEVELS DRY FCST BUFR SOUNDINGS
AN INCREASE IN THE UPPER LEVEL MOISTURE THIS AFTN AND TONIGHT. HIGH
TEMPS SHOULD RANGE IN THE LOWER 50S NW TO NEAR 60 IN THE EAST.
TONIGHT...SURFACE RIDGE EXTENDS NE INTO THE CAROLINAS TODAY FROM A
SFC HIGH ACROSS AL/GA. FAIR WEATHER WITH PERIODS OF HIGH CLOUDS ARE
EXPECTED TONIGHT. LOW TEMPS TONIGHT SHOULD RANGE BETWEEN 29-34 DEG
F.
SUNDAY...SURFACE RIDGE MOVES EAST OFFSHORE ON SUNDAY. A WEAK SFC
TROUGH IS PROGGED TO DEVELOP IN THE LEE OF THE MTNS DURING THE DAY.
BOTH OF THE 26/00Z ECMWF AND CANADIAN INDICATE SOME VERY LIGHT QPF
SHOULD FALL ACROSS THE COASTAL REGION OF THE CAROLINAS AND GA ON SUN
AFTN OR EVE. QPF AMOUNTS ARE SMALL AND THIS SCENARIO IS NOT
SUPPORTED BY OPERATIONAL NAM/GFS AND THE 26/03Z SREF SO WILL
DISCOUNT POPS FOR NOW BUT PLAY UP CLOUDS A BIT. HIGH TEMPS IN THE
52-58 RANGE LOOK GOOD.
SUNDAY NIGHT...850 MB TROUGH WILL MOVE ACROSS THE STATE LATE SUNDAY
NIGHT AND MONDAY. THE SIGNIFICANT COLD ADVECTION DOES NOT START
ACROSS WESTERN SECTIONS OF CWA UNTIL WELL AFTER MID NIGHT WITH BEST
COLD ADVECTION LATER ON MONDAY. WILL KEEP LOW TEMPS MODERATED A BIT
WITH LOWS IN THE 29-35 RANGE.
&&
.SHORT TERM /MONDAY THROUGH WEDNESDAY/...
AS OF 320 AM SATURDAY...
AN UPPER TROUGH PROGGED TO CROSS THE CWA ON MONDAY MORNING WILL
BRING A DECENT VORTICITY LOBE ACROSS THE AREA BY 18Z. ALTHOUGH
THERE MAY BE DECENT DPVA WITH THIS UPPER TROUGH...COLD ADVECTION
WILL HELP TO NEGATE ANY FORCING FOR ASCENT (BEST Q-VECTOR
CONVERGENCE REMAINS WELL NORTH OF THE CWA) AND A DRY AIRMASS WITH
PWS AT OR BELOW 0.25" WILL KEEP THINGS DRY ON MONDAY. GIVEN THAT
THICKNESS FALL OR HOLD STEADY THROUGHOUT THE DAY AS THE COLD FRONT
PUSHES EAST...HAVE ELECTED TO ELAN TOWARDS NAM MOS GUIDANCE WITH
HIGHS IN THE 43-47 RANGE. LOWS MONDAY NIGHT IN THE MID TO UPPER 20S.
SHORTWAVE RIDGING ALOFT ON TUESDAY WILL LEAD TO A LITTLE MODERATION
AS A SURFACE HIGH SLIDES EAST TOWARDS THE MID ATLANTIC STATES.
EXPECT MOSTLY SUNNY SKIES AND TEMPS BACK TO NEAR NORMAL...47-52.
CLOUDS WILL BEGIN SPREAD BACK INTO THE AREA ON WEDNESDAY WITH TEMPS
FALLING BACK BELOW NORMAL AS A LATE WEEK SYSTEM TAKES SHAPE ALONG
STORM TRACK THAT HAS BEEN IN PLACE FOR SOME TIME NOW.
&&
.LONG TERM /WEDNESDAY NIGHT THROUGH FRIDAY NIGHT/...
AS OF 320 AM SATURDAY...
CONCERNING THE LATE WEEK SYSTEM....
MODELS CONTINUE TO INDICATE A POSSIBLE HYBRID CAD EVENT BY THE END
OF THE WEEK AS A FAIRLY STRONG 1032MB HIGH SETS UP OVER THE MID
ATLANTIC STATES...A DEEP UPPER TROUGH DEVELOPS OVER THE EASTERN
US...AND A LOW PRESSURE SYSTEM TRACKS FROM THE GULF TO THE EAST
COAST. HOWEVER...SOME SIGNIFICANT MODEL DIFFERENCES HAVE DEVELOPED
OVER THE PAST COUPLE OF RUNS...ESPECIALLY WITH THE ECMWF WHICH
SIGNIFICANTLY LATER WITH ITS ARRIVAL OF PRECIP AND SURFACE LOW
DEVELOPMENT.
CURRENTLY...MODELS DEPICT A SERIES SHORTWAVES THAT WILL DRIVE THE
EVOLUTION OF THE LATE WEEK STORM SYSTEM. THE GFS PRODUCES A
STRONGER LEAD SOUTHERN STREAM SHORTWAVE THAT DRIVES A SURFACE LOW
FROM THE GULF OF MEXICO WED NIGHT TO THE CAROLINA COAST THURS
MORNING...BRINGING PRECIP TO THE CWA AS EARLY AS WED NIGHT AND
POTENTIALLY GIVING A BETTER CHANCE AT MIXED PRECIP IN THE NW BASED
ON
LOW LEVEL THICKNESS EVOLUTION. THEN...A TRAILING NORTHERN STREAM
WAVE DIVES SOUTH THROUGH THE MISSISSIPPI VALLEY REGION. WITH THE
SURFACE LOW WELL OFFSHORE BY THURS EVENING... THE MAIN BAROCLINIC
ZONE IS PULLED FURTHER EAST AND THERE IS LITTLE IMPACT OVER CENTRAL
NC WHEN THE TRAILING WAVES FINALLY ROUND THE BASE OF THE UPPER
TROUGH.
THE ECMWF ON THE OTHER HAND HAS A SLOWER DEVELOPMENT OF THE
FIRST SYSTEM ON WED NIGHT (OWING TO A WEAKER LEAD SHORTWAVE)...AND
THUS WHEN THE TRAILING WAVE APPROACHES (POSSIBLY PHASING WITH A
SECOND SOUTHERN STREAM WAVE)...CYCLOGENESIS ALONG THE COAST IS
DELAYED UNTIL LATE FRIDAY..WHICH LEADS TO CONTINUED PRECIP CHANCES
ON FRIDAY AND A POTENTIAL NOR'EASTER AS IT STANDS RIGHT NOW...THIS
SCENARIO WOULD MORE LIKELY BE ALL RAIN.
GIVEN THE ABOVE...HAVE ELECTED NOT TO MAKE SIGNIFICANT CHANGES TO
THE EXTENDED FORECAST OTHER THAN TO SHOW THAT THURSDAY AND FRIDAY
WILL BE CLOUDY WITH HIGHS BELOW NORMAL AND A PERIOD OF PRECIP
BETWEEN THURSDAY MORNING AND MIDDAY FRIDAY.
&&
.AVIATION /12Z SATURDAY THROUGH TUESDAY/...
AS OF 635 AM SATURDAY...
COMPLEX SFC PATTERN EARLY THIS MORNING ACROSS THE MID ATLANTIC WITH
A DEPARTING SFC WAVE MOVING FROM NE NC INTO SOUTHEAST VA.
WIDESPREAD LOW CIGS AND VSBYS EARLIER TONIGHT HAVE GENERALLY
IMPROVED ON THE WHOLE WHILE SOME LOCATIONS...ESPECIALLY IN THE TRIAD
ARE STILL CONFINED IN IFR/LIFR CONDITIONS.
WEAK HIGH PRESSURE WILL BUILD INTO THE REGION FROM THE SOUTHWEST
TODAY BRINGING COOL AND DRIER AIR INTO THE LOW LEVELS OF THE ATMOS.
DEGRADED AVIATION CONDITIONS EARLY THIS MORNING WITH IFR/LIFR
CONDITIONS WILL GIVE WAY TO IMPROVING CONDITIONS LATER THIS MORNING
AND ESPECIALLY THIS AFTERNOON. TODAY...CIGS AND VSBYS IMPROVE WITH A
LIGHT W TO NW FLOW IN THE AFTN. EXPECT VFR CONDITIONS TO ARRIVE
AROUND OR JUST BEFORE MIDDAY WITH BKN CLOUDS AROUND 2KFT GIVING WAY
TO BKN CLOUDS AT AROUND 20KFT DURING THE AFTN.
LOOKING FURTHER AHEAD THROUGH EARLY NEXT WEEK...MAINLY FAIR WEATHER
WITH VFR CONDITIONS ARE EXPECTED THROUGH TUESDAY AS HIGH PRESSURE
GENERALLY CONTROLS THE WEATHER.
&&
.RAH WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SYNOPSIS...BLAES
NEAR TERM...BLAES
SHORT TERM...SMITH
LONG TERM...SMITH
AVIATION...BLAES
