-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KLWX 071146
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
646 AM EST SAT DEC 7 2013

.SYNOPSIS...
HIGH PRESSURE WILL BRIEFLY BUILD OVERHEAD TODAY. LOW PRESSURE
WILL DEVELOP AND APPROACH FROM THE SOUTHWEST TONIGHT INTO EARLY
SUNDAY. THIS SYSTEM WILL IMPACT THE AREA WITH WINTRY PRECIPITATION
SUNDAY INTO MONDAY. AN UPPER-LEVEL DISTURBANCE WILL PASS THROUGH
THE AREA TUESDAY. CANADIAN HIGH PRESSURE WILL BUILD OVERHEAD
DURING THE MIDDLE OF NEXT WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
COLD FRONT WILL CONTINUE TO PUSH SOUTH AND EAST OF THE REGION THIS
MORNING. RADAR INDICATES BACK EDGE OF ANAFRONTAL RAIN HAS REACHED
SRN MD. THIS PRECIPITATION WILL CONTINUE TO SLIDE EWD THIS
MORNING.

FURTHER WEST...SEVERAL SURFACE OBS WEST OF THE POTOMAC HIGHLANDS
INDICATE LIGHT SNOW...ALONG WITH A BAND MOVING ACROSS SOUTH
CENTRAL WV ON RADAR. MODELS INDICATE LOW TO MID LEVELS WILL DRY
OUT AS THE MORNING PROGRESSES...WITH SNOW ENDING ACCORDINGLY. STILL
COULD SEE POTENTIAL FOR LIGHT ACCUMULATION IN THE HIGHLANDS...BUT
LESS THAN AN INCH FOR THE REST OF THE MORNING.

THE COLD FRONT WILL CONTINUE TO MOVE AWAY FROM THE AREA
TODAY...WHILE HIGH PRESSURE BUILDS IN FROM THE WEST. CLOUDS ARE
EXPECTED TO ERODE OVER THE COURSE OF THE DAY AS DRY AIR FILERS
IN...WITH PARTLY TO MOSTLY SUNNY SKIES EXPECTED BY THIS AFTERNOON.
N-NW WINDS EXPECTED...SOMETIMES GUSTY WITH COLDER AIR BUILDING IN
ALOFT. BIAS CORRECTED NAM/GFS USED FOR HIGHS TODAY...RANGING FROM
THE UPPER 20S OVER THE POTOMAC HIGHLANDS TO THE MID 40S OVER
PORTIONS OF THE PIEDMONT AND SRN MD.

HIGH PRESSURE BUILDS ACROSS PA AND NRN PORTIONS OF THE FCST AREA
OVERNIGHT...WHILE CYCLOGENESIS BEGINS ALONG THE FRONTAL BOUNDARY TO
OUR SOUTH. MOST OF THE AREA WILL BE DRY...ALTHOUGH SOME LIGHT SNOW
MAY BEGIN OVER THE SOUTHERNMOST COUNTIES IN THE PREDAWN HOURS.
LOW-LEVEL CAD IS EXPECTED TO DEVELOP DUE TO THE HIGH TO OUR NORTH.
LOW TEMPS RANGE FROM THE UPPER TEENS OVER THE POTOMAC HIGHLANDS
TO AROUND 30 IN METRO BALTIMORE/WASHINGTON.
-- End Changed Discussion --

&&

.SHORT TERM /SUNDAY THROUGH MONDAY/...
-- Changed Discussion --
SYNOPTICALLY...THE WX SITUATION REMAINS CONSISTENT RUN-TO-RUN. SFC
HIPRES WL BE LOCATED ACRS THE NERN CONUS SUN MRNG...WHILE FAST WSWLY
MID-UPR FLOW RESIDES ABV IT. MSTR...W/ A RATHER SHARP LEADING
EDGE...WL OVERSPREAD AREA DURING THE MRNG HRS. SINCE AMS WL BE
SUFFICIENTLY COLD...SUPPLIED BY NLY FLOW AND ENHANCED BY EVAP
COOLING...PCPN AT ONSET WL BE ALL SNOW. A RIBBON FGEN FORCING NOTED
IN THIS AREA...SO A QUICK BURST OF SNFL LKLY. THEREAFTER...A
VIGOROUS THRUST OF H8 WAA WL GLIDE ATOP THE COLD POOL...INTRODUCING
MIXED PCPN. APPEARS AS THO THE WARM NOSE WL BE MORE SHALLOW
INLAND...AND DEEPER NEAR THE COAST DUE TO MARINE AIR. TRANSITION WL
GO FM SNW TO PL AND EVENTUALLY TO FZRA DURING THE AFTN...W/ SFC
TEMPS REACHING OR EXCEEDING 32F ALONG THE COAST FOR JUST RA THERE.

SFC RDG WL BE PINCHED OFF SUN NGT AS CYCLOGENESIS INITIATES OFF THE
CST. UP TO THAT PT...FORCING WL BE DRIVEN PURELY BY ISENT LIFT AND
JET DYNAMICS. WHILE SFC WARMTH WL ATTEMPT TO PROGRESS INLAND...SETUP
FOR CAD APPEARS TO BE PRETTY STRONG...AND WL EMPH FZRA THRU MUCH OF
SUN NGT...SPCLY ALONG AND W OF BLURDG. HV SLOWED TRANSITION TO RA BY
SVRL HRS...SPCLY FOR THE NRN SHEN VLY/PTMC HIGHLANDS. NO NEED TO
EXTEND ENDING TIME OF WATCH...BUT GRIDS NOW PUSHING UP AGAINST THAT
BACK END...W/ A FRZA MENTION NOW INTO MON MRNG W OF I-95.

CWFA WL BE IN DEF BAND BY MON MRNG. PCPN RATES SHUD BRIEFLY INCREASE
BEFORE AXIS MVS OFFSHORE. AS LOW DEPARTS...WL BE ABLE TO GET WINDS
TO VEER SWLY...WHICH IS THE FINAL PIECE TO ENSURE A TRANSITION TO
RA.

WINTER STORM WATCHES ALREADY IN PLACE. SNOW ACCUMS ADJUSTED A LTL TO
FIT INIT BURST OF SNW. AFTER THAT...RATES SHUD BE ON THE LIGHTER
SIDE AS THE TRANSITIONS TAKE PLACE. WHILE AM CONFIDENT THAT THERE WUD
BE A PROLONGED PD OF FZRA W OF THE BLURDG...ICE ACCRETION IS A MORE
DIFFICULT ITEM TO NAIL DOWN. HIER RAFL RATES DOES NOT NECESSARILY
LEAD TO GREATER ACCRETION...AND A COLDER SOLN /STILL PSBL/ WUD
ADJUST FCST TO LESS FZRA AND MORE PL. WHILE AM BCMG FAIRLY CERTAIN
THAT WRNGS WL BE NEEDED AT SOME POINT...FEEL ITS PRUDENT TO RECEIVE
ANTHR MDL RUN OF SO TO ASSESS WHEN/WHERE TO PLACE IT.
-- End Changed Discussion --

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
CDFNT WL REMAIN STALLED SE OF CWFA MON NGT...W/ AN ADDTL RIPPLE CPLD
W/ A DEEPENING TROF AXIS ACRS THE GRTLKS COAXING IT EWD TUE MRNG. WL
KEEP POPS IN FCST THRU THEN...AS RA OR SNW AS THERMALLY APPROPRIATE.
AFTER THAT...COLD CNDN HIPRES BLDG SEWD THRU THE END OF THE WK.

&&

.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
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SOME MVFR/IFR CIGS LINGER THIS MORNING...BUT CONDITIONS IMPROVE
THROUGHOUT THE DAY AS A COLD FRONT MOVES AWAY FROM THE REGION AND
HIGH PRESSURE BUILDS IN. WINDS N-NW AROUND 10-15KT WITH SOME GUSTS
TO 20KT.

VFR CONDITIONS CONTINUE OVERNIGHT WITH N-NW WINDS AROUND 5-10KT.

SNOW AND SLEET ARE EXPECTED ACROSS THE TERMINALS SUNDAY MORNING
BEFORE CHANGING TO FZRA SUNDAY AFTERNOON. FZRA WILL CONTINUE THROUGH
SUNDAY NIGHT FOR CHO-MRB-IAD. LOWER CONFIDENCE IN CONSTANT FZRA
FOR BWI-MTN-DCA DUE TO TEMP MODERATING. MVFR/IFR CONDITIONS ARE
POSSIBLE DURING THIS TIME.

HIGH PRESSURE MOVES INTO THE REGION TUESDAY AND CONTINUES THROUGH
THE MIDDLE OF THE WEEK.
-- End Changed Discussion --

&&

.MARINE...
SMALL CRAFT ADVISORY IN EFFECT FOR ALL WATERS SATURDAY...WITH GUSTY
N-NW WINDS BEHIND THE COLD FRONT THAT MOVED THROUGH OVERNIGHT. SCA
EXPIRES THIS EVENING OVER THE NRN POTOMAC RIVER ZONES AS HIGH
PRESSURE BUILDS IN. SCA REMAINS IN PLACE OVER THE BAY AND LOWER
TIDAL POTOMAC...WHERE A PRESSURE GRADIENT SHOULD REMAIN IN PLACE
BETWEEN HIGH PRESSURE TO THE NORTH AND OFFSHORE LOW PRESSURE.

SNOW AND SLEET ARE EXPECTED SUNDAY MORNING BEFORE CHANGING OVER A
MIX OF FZRA-SLEET-RAIN SUNDAY AFTERNOON. ICE ACCUMULATION IS
POSSIBLE MAINLY NEAR THE LAND AS WATER TEMPS ARE STILL IN THE MID
40S. MIXING WL BE IMPEDED THRU THIS TIME FRAME. NLY WNDS WL VEER
NELY SUN...AND ELY SUN NGT. SPDS SHUD BE AOB 10 KT.

LOPRES WL DVLP OFFSHORE MON AND MV NEWD BY TUE. WNDS WL INCR IN
THE WAKE OF THIS LOW...RELATIVE TO BLDG HIPRES ACRS THE GRTLKS. SCA
CONDITIONS POSSIBLE MID WEEK WITH N-NW FLOW OVER THE WATERS.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
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DC...WINTER STORM WATCH FROM SUNDAY MORNING THROUGH MONDAY MORNING
     FOR DCZ001.
MD...WINTER STORM WATCH FROM SUNDAY MORNING THROUGH MONDAY MORNING
     FOR MDZ003-501-502.
     WINTER STORM WATCH FROM SUNDAY MORNING THROUGH MONDAY MORNING
     FOR MDZ004>007-009>011-013-014-016.
VA...WINTER STORM WATCH FROM SUNDAY MORNING THROUGH MONDAY MORNING
     FOR VAZ025>031-036>038-503-504.
     WINTER STORM WATCH FROM SUNDAY MORNING THROUGH MONDAY MORNING
     FOR VAZ039-040-042-050>057-501-502.
WV...WINTER STORM WATCH FROM SUNDAY MORNING THROUGH MONDAY MORNING
     FOR WVZ050>053-055-501>506.
MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EST SUNDAY FOR ANZ530>534-537-
     539>541-543.
     SMALL CRAFT ADVISORY UNTIL 6 PM EST THIS EVENING FOR ANZ535-
     536-538-542.
-- End Changed Discussion --

&&

$$
SYNOPSIS...KCS
NEAR TERM...KCS
SHORT TERM...HTS
LONG TERM...HTS
AVIATION...KCS/HTS
MARINE...KCS/HTS