FXUS61 KLWX 051644 AAC
AFDLWX
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1144 AM EST SAT DEC 5 2009
.SYNOPSIS...
LOW PRESSURE WILL INTENSIFY AND TRACK NORTHEAST ALONG THE
SOUTHEAST US COAST TODAY...AND THEN MOVE OUT TO SEA TONIGHT. HIGH
PRESSURE WILL SETTLE IN OVER THE AREA SUNDAY AND WILL BE CENTERED
OVER THE REGION BY SUNDAY EVENING. A WEAK DISTURBANCE WILL PASS
OVERHEAD MONDAY. THAT WILL BE FOLLOWED BY A LARGE STORM SYSTEM ON
TUESDAY NIGHT AND WEDNESDAY.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
QUICK UPDT TO UPGRADE TO WINTER STORM WARNING FOR PORTIONS OF
POTOMAC HIGHLANDS...AS SNOW TOTALS THUS FAR SUGGEST THAT SNOW
AMOUNTS WILL REACH 5 TO 8 INCH BY THE TIME SNOW ENDS THIS EVENING.
PREVIOUS DISCUSSION FOLLOWS...
SYNOPTICALLY...COASTAL LOW STILL FORMING ALONG CAROLINA OUTER
BANKS. UPR SYSTEM MVG NEWD INTO SW VA...WHERE BACK EDGE OF
DEFORMATION BAND OF SNOW BEGINNING TO CROSS. LARGE SCALE LIFT
ASSOCIATED WITH RIGHT ENTRANCE REGION OF UPR JET CONTS TO PRODUCE
WIDESPREAD PRECIP ACROSS ENTIRE LWX CWA. RAISED TOTAL SNOW
ACCUMULATION BETWEEN ONE HALF AND ONE INCH...AS EARLIER TRANSITION
TO SNOW SHUD ALLOW FOR MORE WIDESPREAD 3 TO 4 INCH AMOUNTS WEST OF
URBAN CORRIDOR. AREAS WEST OF BLUE RIDGE HAVE RECEIVED BETWEEN ONE
AND THREE INCHES THIS MORNING. ADDITIONAL TWO TO FOUR INCHES XPCD
IN WARNING AREA...WITH HIGHEST STORM TOTALS OVER HIGHER
ELEVATIONS. E OF BLUE RIDGE...TEMPERATURES FALLING TO JUST ABOVE
FREEZING ALONG AND W OF I 95...WITH PRECIP TYPE ALL SNOW. RN/SN
MIX THROUGH URBAN CORRIDOR WITH ALL RAIN ACRS LOWER SOUTHERN MD.
NO CHANGES TO HEADLINES WITH MORNING UPDT. MODIFIED HRLY GRIDS FOR
QUICKER TRANSITION TO SNOW AND EARLIER ONSET OF ACCUMULATION.
OTHERWISE...ONLY MINOR ADJUSTMENTS TO REFLECT CURRENT CONDITIONS.
PREVIOUS DISCUSSION FOLLOWS...
MID/UPR LEVEL DIVERGENCE HAS ALLOWED PRECIP SHIELD TO EXPAND AND
NOW ENCOMPASSES ALL OF CWA...THEREFORE HAVE RAISED POPS TO 100
PERCENT THROUGH THE MRNG...CONTG THRU MUCH OF AFTN. PRECIP MIXING
WITH/CHANGING TO SNOW W OF BLUE RIDGE AS OF 800 AM EST...WITH
MINOR ACCUMULATION OVER HIGHER ELEVATIONS. A FEW FLAKES MIXING IN
E OF BLUE RIDGE/W OF I 95...BUT MAJORITY OF PRECIP SHUD RMN RAIN
THRU LT MRNG. NO CHANGES TO WINTER HEADLINES ATTM...AND OVERALL
END TIMING OF PRECIP LOOK ON TRACK. ADJUSTED HRLY GRIDS TO REFLECT
CURRENT CONDS...WILL BE UPDTD PRODUCTS ACCORDINGLY. PREVIOUS
DISCUSSION FOLLOWS...
LOPRES DVLPG OFF THE CAROLINAS ELY THIS MRNG...ALNG CSTL FNT.
MEANWHILE...A 2ND LOPRES CNTR CUD BE FOUND IN THE GLFMEX...THO ITS
BEEN WKNG SINCE 04Z...SUGGESTING THAT ENERGY TRANSFER TO THE CSTL
SYSTM HAS BEGUN. THE LONG SWATH OF PCPN ASSOC W/ THE CSTL FNT HAS
BEEN BACKING WWD...AND LGT PCPN HAS BEGUN ACRS THE TIP OF ST MARYS
CNTY. HWVR...W/ TEMPS WELL INTO THE 40S...NO PTYPE QSTN-- ITS -RA.
THE KEY TO WATCH TDA WL BE THE PROGESS OF THE CSTL LOW...WHICH WL
DRAW COLD AIR SEWD. H5 TROF AXIS...TAKING ON A NEG TILT AS THE DAY
TRANSPIRES...AND RRQ OF H3 JET WL BE PROVIDING A FVRBL DYNAMIC SETUP
FOR PCPN TO DVLP THIS MRNG. THE JET STREAK WL BE MORE OF THE MRNG
LIFTING TRIGGER...THE H5 TROF WL BE ARND IN THE AFTN/EVE. SO...THE
CATALYST FOR PCPN PRESENT.
NOW...FOR THE TEMPS. BASED ON LTST MDL GDNC...THATS NOT AS MUCH OF A
GIVEN...SPCLY FOR SERN CNTYS...WHERE RAFL TO DOMINATE AT ONSET.
HWVR...H10-8 TKNS VALUES DROPPING THRU AFTN...PRBLY A RSLT OF EVAP
COOLING AND H8 CAA...WHICH WL PERMIT A CHGOVR TO SNW. BUT...CRIT
TKNS LINES STRUGGLE TO MAKE IT TO I-95 DURING DAYLIGHT HRS. SEEING
SIMLR RESPONSE IN TEMP FIELDS/MOS TEMP VALUES. THEREFORE...FEEL MOST
CONFIDENT THAT SNW WL DOMINATE IN HIGHLANDS/SHEN VLY/ALNG THE
BLURDG. CONCURENTLY THE QPF WL BE THE HIEST SRN HALF OF CWFA...
NEARER PATH OF H8 LOW. THAT MEANS THE CRRNT WRNG AREA AT
INTERSECTION OF MSTR AND COLD TEMPS...AND DOES INDEED STAND THE BEST
CHC AT GOOD SNW TTLS.
OVRALL...SEE LTL NEED TO MAKE SUBSTANTIVE CHGS TO FCST. HV REFINED
THE TIMING A LTL...BACKING OFF ON ELY MRNG PCPN...SPCLY ACRS NERN
MD. THAT/S IN LINE W/ RDR TRENDS. STILL PERFER FASTER NAM AS ITS
INITIALIZED CSTL LOW BETTER...AND STILL SUGGESTS THAT PCPN WL BE
AFTR 12Z FOR MOST OF CWFA. IN THE END...WRNG/ADVY STRUCTURE WL STAND
AS IS.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SUNDAY/...
SFC LOW WL QUICKLY MV NE OF CWFA AS IT DEEPENS TNGT. THAT WL DRAW
COLD /SUBFRZG/ AIR ACRS REST OF CWFA AS THE DEFORMATION AXIS
CROSSES. END RSLT WL BE SNWFALL MAKING IT S/E OF DC TO THE BAY PRIOR
TO ALL PCPN ENDING. BLYR TEMPS WL STILL BE MARGINAL THO...SO CHC AT
ACCUM SNW DWINDLE FURTHER OUT ONTO THE TIP OF SRN MD. BUT THE AMS
ANOMOLOUS ENUF AND CONTAINS SUFFICIENT DYNAMIC SUPPORT TO PRODUCE
ACCUMS ACRS ENTIRE CWFA...JUST NOT TO ADVY CRIT /AOB AN INCH/ ACRS
CALVERT/ST MARYS.
ALSO IN THE WRAP ARND WL BE A PD UP UPSLP SNW FOR THE ALLEGANY FNT.
ATTM DONT THINK IT WL LAST LONG AS LARGE/STRONG HIPRES BLDS INTO
APPLCHNS OVNGT...QUIKLY LWRG INVSN HGTS.
ANTICIPATING SNWCVR AND PERHAPS PARTIALY CLRG PER CAA/DRY AIR
ADVCTN...HV UNDERCUT MOS BY A PINCH. ENPHASIS WL BE BEST IN THE
W...AS THOSE SXNS HV BEST CHC AT DCPLG.
&&
.LONG TERM /SUNDAY THROUGH FRIDAY/...
HIGH PRESSURE WILL SETTLE IN ON SUNDAY WITH SUNNY SKIES...HOWEVER
THE HIGH WILL BE CENTERED ON THE REGION SUNDAY NIGHT AND WITH CALM
WINDS AND SOME SNOW COVER LIKELY WEST OF I-95...TEMPS WILL TANK.
A VERY WEAK COLD FRONT SLIDES THRU MONDAY WITH A CHANCE OR SLIGHT
CHC OF RAIN SHOWERS WITH DAYTIME TEMPS IN THE 40S.
NEXT BIG THING WILL BE A VERY LARGE STORM SYSTEM THAT WILL MOVE
ACROSS THE S STATES BEFORE SWEEPING UP TO THE NORTHEAST OVER OUR
REGION TUE NIGHT INTO WED. COULD BE SOME MIXED WINTRY PRECIP ON TUE
NIGHT.
COLD/COOL AND BLUSTERY FOR WED NIGHT THRU THU NIGHT BEFORE HIGH
PRESSURE SETTLES IN OVER THE REGION ON FRIDAY.
&&
.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
MVFR CONDS IN RN/SN AT DCA AND BALTIMORE TAF SITES WILL TRANSITION
TO IFR AS SNOW BECOMES PREVALENT P-TYPE BY 17Z. IFR OR BELOW
VSBY/CIGS ELSEWHERE. XPCD SN TO CONT THRU 0Z...WITH VSBY UNDER 1SM
AND CIGS AOB 500FT. AFTER 0Z...MVFR CONDS...WITH VFR CONDS
BEGINNING SHORTLY THEREAFTER AT KCHO...EXPANDED NEWD TO ALL
AIRPORTS BY AROUND 6Z. PREVIOUS DISCUSSION FOLLOWS...
VFR CONDITIONS EXPECTED FOR THE EARLY PART OF THE WEEK BEFORE THE
NEXT SYSTEM BRINGS LOW CIGS AND VSBYS TUE NIGHT AND WED. STRONG
WINDS BEHIND THAT STORM FOR WED NIGHT THRU THU NIGHT.
&&
.MARINE...
LOPRES WL DVLP OFF THE CAROLINAS TDA...DEEPENING AND MVG E OF
DELMARVA TNGT. WHILE WNDS MOSTLY AOB 10 KT ATTM /TPLM2 16KT/ THAT WL
SUPPORT SCA CONDS BGNG AFTR DAYBREAK. HV TRIMMED ONSET...SPCLY FOR
UPR PTMC WHERE FETCH AND DISTANCE NOT AS FVRBL. LOW PASSING BY
TAFTN...WHICH WL BE WHEN PCPN WL BE HVIEST AND WNDS STRONGEST /SHUD
HV G30KT ON THE MAIN CHANNEL BAY/. AFTR THAT...DIMINISHING WNDS AS
LOW DEPARTS. HIPRES BLDS QUICKLY FM W...AND WL END SCA ACRS UPR PTMC
AT 07Z.
SMALL CRAFT CONDITIONS WILL LINGER ON THE BAY INTO SUNDAY BEFORE
WINDS ENTIRELY SUBSIDE. NEXT SHOT AT HAZARDOUS MARINE WEATHER WILL
BE WITH A STORM SYSTEMS ON TUE NIGHT AND WED. THEN STRONG WINDS AND
SMALL CRAFT ADVISORIES ARE EXPECTED BEHIND THE STORM FOR WED NIGHT
THRU THU NIGHT.
&&
.LWX WATCHES/WARNINGS/ADVISORIES...
DC...WINTER WEATHER ADVISORY UNTIL 11 PM EST THIS EVENING FOR
DCZ001.
MD...WINTER WEATHER ADVISORY UNTIL 11 PM EST THIS EVENING FOR
MDZ011-013-014-016.
WINTER STORM WARNING UNTIL 7 PM EST THIS EVENING FOR MDZ501-
502.
WINTER WEATHER ADVISORY UNTIL 9 PM EST THIS EVENING FOR
MDZ003>007-009-010.
VA...WINTER WEATHER ADVISORY UNTIL 11 PM EST THIS EVENING FOR
VAZ054>057.
WINTER STORM WARNING UNTIL 7 PM EST THIS EVENING FOR VAZ021-
025>027-029-030-036>040.
WINTER WEATHER ADVISORY UNTIL 9 PM EST THIS EVENING FOR VAZ028-
031-041-042-050>053.
WV...WINTER STORM WARNING UNTIL 7 PM EST THIS EVENING FOR WVZ050-
054-055-501>504.
WINTER WEATHER ADVISORY UNTIL 9 PM EST THIS EVENING FOR
WVZ051>053.
MARINE...SMALL CRAFT ADVISORY UNTIL 10 AM EST SUNDAY FOR ANZ531>534-
538>541-543.
SMALL CRAFT ADVISORY UNTIL 5 AM EST SUNDAY FOR ANZ530-537-542.
SMALL CRAFT ADVISORY UNTIL 2 AM EST SUNDAY FOR ANZ535-536.
&&
$$
SYNOPSIS...CAS
NEAR TERM...SBK/HTS
SHORT TERM...HTS
LONG TERM...CAS
AVIATION...SBK/CAS/HTS
MARINE...SBK/CAS/HTS
