FXUS62 KRAH 261737
AFDRAH
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
1237 PM EST SAT DEC 26 2009
.SYNOPSIS...
WEAK HIGH PRESSURE WILL BUILD INTO NC FROM THE GULF COAST STATES
TODAY THROUGH SUNDAY.
&&
.NEAR TERM /THROUGH SUNDAY NIGHT/...
AS OF 1030 AM SATURDAY...
15Z SFC ANALYSIS SHOWED 1011 MB LOW PRESSURE CENTERED NEAR VIRGINIA
BEACH. 1001 MB LOW PRESSURE WAS CENTERED OVER IOWA. 1039 MB HIGH
PRESSURE WAS CENTERED OVER NEW BRUNSWICK (CANADA)...WITH A SFC RIDGE
AXIS EXTENDING SOUTH THROUGH NEW ENGLAND. 1021 MB HIGH PRESSURE WAS
CENTERED OVER THE DEEP SOUTH...WITH A RIDGE AXIS EXTENDING NORTH
INTO THE EASTERN TN/OH VALLEYS. ALOFT...12Z RAOB ANALYSIS SHOWED A
DEEP/EXPANSIVE UPPER LOW IN THE MIDWEST...CENTERED OVER SOUTHERN
WISCONSIN. SOUTHWEST FLOW ALOFT WAS NOTED OVER THE CAROLINAS AND
SOUTHEAST STATES. A WEAK TROUGH WAS NOTED IN THE LOWER LEVELS
(925-850 MB) OVER NC/VA.
TODAY:
CHALLENGING CLOUD COVER AND TEMPERATURE FORECAST TODAY...WITH THE
FORECAST HINGING ON HOW LONG IT TAKES THE STAGNANT POOL OF LOW LEVEL
MOISTURE TO SCATTER OUT. THE 12Z GSO SOUNDING SHOWED A VERY SHALLOW
SATURATED LAYER IN THE LOWEST LEVELS...NO MORE THAN 1500-3000 FT
THICK...CAPPED OFF BY A STRONG/ DRY SUBSIDENCE INVERSION ABOVE 900
MILLIBARS. ALTHOUGH VERY DRY AIR IS PRESENT IN THE MID-LEVELS...
MOISTURE EMANATING FROM THE SUBTROPICAL PACIFIC HAS QUICKLY MOVED
INTO THE CAROLINAS THIS MORNING VIA THE SUBTROPICAL JET...RESULTING
IN BROKEN/OVERCAST CEILINGS AT 20-25 KFT AS WELL. THE LATEST
FORECAST MODELS SHOW THE LOW LEVEL TROUGH AND WEAK SFC LOW CURRENTLY
OVER EASTERN NC/VA LIFTING NORTHEAST INTO THE DELMARVA THIS
AFTERNOON...WITH SFC-925MB FLOW ACROSS CENTRAL NC BECOMING
INCREASINGLY NORTHWESTERLY AT ~10 KT. THIS SHOULD HELP TO SLOWLY
ERODE AND SCATTER OUT THE SHALLOW/STAGNANT POOL OF LOW LEVEL
MOISTURE IN PLACE ACROSS THE AREA FROM WEST TO EAST THROUGH THE DAY.
LATEST OBSERVATIONAL TRENDS SUPPORT THIS CONCLUSION...WITH
INT/GSO/EXX/HBI SITES ALREADY SCATTERED OUT AS OF 15Z...AND LATEST
VIS SAT IMAGERY SHOWING THE SHALLOW POOL OF MOISTURE ERODING SLOWLY
TOWARD THE EAST/SE. FCST SOUNDINGS SUGGEST THAT THE TRIANGLE SHOULD
SCATTER OUT BY ~18Z...WITH EASTERN PORTIONS OF THE AREA (I.E. RWI)
NOT SCATTERING OUT UNTIL CLOSER TO 21Z. AS A RESULT...WILL FORECAST
CLOUDY SKIES IN THE EAST FOR MUCH OF THE DAY...WITH PARTLY TO MOSTLY
CLOUDY SKIES IN THE WEST...PRIMARILY DUE TO A FAIR AMOUNT OF UPPER
LEVEL CLOUD COVER. HAVE LOWERED MAX TEMPS OVER MUCH OF THE AREA
TODAY...CLOSER TOWARD THE COOLER METMOS GUIDANCE...RANGING FROM ~54F
IN THE COASTAL PLAIN...TO 55-56F IN THE TRIANGLE...AND LOWER 50S IN
THE TRIAD. THESE HIGH TEMPS COULD EASILY BUST BY SEVERAL DEGREES IN
SOME LOCATIONS...DEPENDING ON THE TIMING OF THE EROSION OF THE
SHALLOW MOISTURE POOL. -VINCENT
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 29-34F.
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. -BLAES
&&
.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 /18Z SATURDAY THROUGH TUESDAY/...
AS OF 1230 PM SATURDAY...
24-HR TAF PERIOD:
LINGERING IFR/MVFR CEILINGS WILL AFFECT KRDU THROUGH 18-19Z AT
LATEST...AND THROUGH 19-22Z AT LATEST FOR KFAY/KRWI AS THE
SHALLOW/STAGNANT POOL OF MOISTURE OVER THE AREA CONTINUES TO SLOWLY
ERODE FROM WEST TO EAST. OTHERWISE...EXPECT VFR CONDITIONS TO
PREDOMINATE FROM 00Z THROUGH THE REMAINDER OF THE TAF PERIOD AS HIGH
PRESSURE OVER THE DEEP SOUTH BUILDS NORTHEAST TOWARD THE CAROLINAS.
CANNOT RULE OUT A PERIOD OF REDUCED VISBYS IN FOG BETWEEN 07-12Z
SUN...WITH THE BETTER CHANCE AT KFAY/KRWI TAF SITES. WEST/NW
WINDS AT 4-9 KNOTS ARE EXPECTED THIS AFTERNOON...BECOMING
LIGHT/VARIABLE AFTER 00Z. LIGHT/VARIABLE WINDS ARE EXPECTED TO
BECOME SOUTHERLY AT 4-9 KNOTS BY THE END OF THE TAF PERIOD (~18Z
SUN).
LOOKING AHEAD...VFR CONDITIONS ARE EXPECTED TO PREDOMINATE FROM
SUNDAY EVENING THROUGH WEDNESDAY...WITH THE NEXT CHANCE FOR ADVERSE
AVIATION CONDITIONS HOLDING OFF UNTIL LATE IN THE WEEK. -VINCENT
&&
.RAH WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SYNOPSIS...VINCENT
NEAR TERM...VINCENT/BLAES
SHORT TERM...SMITH
LONG TERM...SMITH
AVIATION...VINCENT
