-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KLWX 080344 AAA
AFDLWX

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1044 PM EST SAT DEC 7 2013

.SYNOPSIS...
HIGH PRESSURE WILL SHIFT EAST TO OUR NORTH THROUGH SUNDAY NIGHT. LOW
PRESSURE WILL DEVELOP AND MOVE NORTHEAST ACROSS THE MID-ATLANTIC
EARLY SUNDAY THROUGH MONDAY...IMPACTING THE AREA WITH WINTRY
PRECIPITATION. AN UPPER- LEVEL DISTURBANCE WILL PASS THROUGH THE
AREA TUESDAY. CANADIAN HIGH PRESSURE WILL BUILD OVERHEAD THEN
THROUGH LATE NEXT WEEK.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
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WINTER STORM WARNING FOR MOST OF THE AREA ROUGHLY WEST FROM
INTERSTATE 95 TO THE ALLEGHENY FRONT. WINTER WEATHER ADVISORIES
ARE UP ELSEWHERE (ALL ZONES HAVE A HEADLINE).

GENERAL PRECIPITATION EXPECTATION REMAINS OF SNOW CHANGING TO
SLEET...THEN FREEZING RAIN...SLOWLY TURNING TO RAIN. COLD AIR
DAMMING IS EXPECTED TO HOLD ON THROUGH SUNDAY NIGHT...MORESO THAN
PROGGED BY LATEST GUIDANCE. THAT KEEPS SOME FREEZING RAIN INTO
MONDAY MORNING FOR THE NRN SHENANDOAH VALLEY AND WEST-CENTRAL
MARYLAND. THE POTENTIAL FOR A QUARTER INCH OF ICE IS QUITE HIGH
FOR MOST OF THE WARNING AREA. FOR VA/MD PIEDMONT AREA...THE
COMBINATION OF PERHAPS A COUPLE INCHES OF SNOW AND A COUPLE TENTHS
INCH ICE WARRANTS A WARNING.

TONIGHT...COLD AHEAD OF THE SYSTEM. DEWPOINTS WILL GENERALLY DROP
INTO THE TEENS AS A NORTH WIND BRINGS IN COLD AIR. MIN TEMPS BELOW
FREEZING ACROSS THE CWA...WITH LOW 20S FOR NRN AND WRN ZONES.
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&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/...
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PREVIOUS FORECAST...
THE CHALLENGES LIE IN DETERMINING P-TYPES AND QUANTITIES. THE
ENTIRE AREA IS XPCTD TO SEE PCPN BEGIN AS SNOW SUN MRNG...
BEGINNING IN CENTRAL VA AND WORKING NWD TO THE PA BRDR. WE ARE
CURRENTLY FCSTG 2-3 INCHES W OF I-81...1 INCH OR LESS IN I-95
CORRIDOR.

LOW PRES IS ALSO XPCTD TO DVLP OFF THE NC CST DURG SUNDAY. THE
COMBINATION OF THIS LOW AND THE NRN HIGH MEANS THE LOW LVL WINDS
SHOULD TURN TO THE E OR NE. THIS WL LKLY HV AN IMPACT ON THE
P-TYPE RCVD FM I-95 AND PTS E - THE WATER TEMP IN THE CHES BAY AND
THE CSTL ATLC IS IN THE M40S: SOME OF THIS HEAT WL BE PICKED UP BY
THE LOW LVL WINDS...WARMING THE ERN PART OF THE CWA.

THERE WL BE LARGE OUTDOOR EVENTS IN BOTH DC AND BALT SUN AFTN. FOR
THE CITIES THOUGHTS ARE THAT MRNG SNOW COULD FALL TO ARND AN
INCH...THEN CHANGING TO IP IN THE AFTN. BUT AT LEAST FOR BALT THE
WARMER MARINE-INFLUENCED AIR SHOULD KEEP TEMPS AOA FRZG. THIS
WOULD BE BENEFICIAL FOR DRIVING BUT STILL NOT A COMFORTABLE DAY TO
BE OUTSIDE FOR HRS.

W OF I-95 IP IS THOUGHT TO BE THE DOMINANT P-TYPE IN THE AFTN...
BUT IT IS ESSENTIAL TO KEEP IN MIND THAT ONE DEG OF WARMING OR
COOLING ALOFT CAN CAUSE A CHG TO THE P-TYPE. IT IS TOUGH TO PICK
UP LARGE ACCUMULATIONS OF SLEET...AND THIS CAN ACTUALLY PACK DOWN
ANY SNOW RCVD 1ST.

SUN NGT SLT WARMING IS XPCTD ALOFT...CHANGING PCPN TO LIQUID. BUT
THE HIGH TO THE N WL KEEP COLD AIR FUNNELING INTO THE AREA...WHICH
WL LKLY LEAD TO ACCUMULATING FRZG RA...WHICH IS THE BIGGEST
CONCERN FM THIS STORM. IT IS PSBL THAT A WINT STORM WRNG MAY BE
NEEDED FOR THE NWRN CORNER OF THE CWA...BUT AS THE ACCRETION WOULD
BE HIGHEST SUN NGT THIS WOULD BE ISSUED BY A LATER SHIFT. TEMPS
IN THE I-95/METRO AREAS WL BE BORDERLINE....AND AT CURRENT ROAD
TEMPS THERE ARE IN THE MU40S...SO FRZG ACCUMS MAY NOT BE AS BAD
THERE. BUT FURTHER W THE SUB FRZG COLD POCKET COULD LAST THRUT THE
NGT...ESPECIALLY IN WRN MD/MINERAL+GRANT/FREDERICK VA.
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&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
REINFORCING HIGH PRESSURE OVER THE CENTRAL CONUS MONDAY...ALONG
WITH A PERSISTENT BERMUDA HIGH...MAINTAINS A SIMILAR PATTERN
ACROSS THE AREA MONDAY NIGHT INTO TUESDAY. ANOTHER WAVE CROSSES
THE AREA WITH A WINTRY MIX ACROSS FORECAST AREA. WILL HAVE TO
WATCH ANOTHER ROUND OF ACCUMULATING RAIN/SNOW/SLEET/FREEZING RAIN.
IT IS WORTH NOTING THAT THE 12Z ECMWF SHUNTS THE PRECIP SOUTH
AFTER THE RAIN ENDS ON MONDAY.

SKIES WILL CLEAR BY TUESDAY NIGHT AS SURFACE RIDGING BUILDS INTO THE
AREA. CANADIAN HIGH PRESSURE OVER THE MISSISSIPPI VALLEY WILL LEAD
TO COLD NORTHERLY FLOW LOCALLY. EURO HAS SOME WESTERLY COMPONENT TO
THIS FLOW WHILE THE GFS ADDS A BIT OF AN EASTERLY COMPONENT. UPSLOPE
SNOW NEAR THE ALLEGHENY FRONT WILL BE POSSIBLE IF THE FLOW DOES
DISPLAY ENOUGH OF A WESTERLY COMPONENT TO GATHER MOISTURE FROM THE
GREAT LAKES UPSTREAM...BUT THIS SCENARIO HAS BEEN LEFT OUT OF THE
GRIDS FOR NOW AS CONFIDENCE IN THE EXACT ORIENTATION OF THE FLOW IS
LOW.

HIGH PRESSURE WILL PASS OVERHEAD ON FRIDAY AND OUT TO SEA THROUGH
THE WEEKEND. THERE IS POTENTIAL FOR A COASTAL LOW TO IMPACT THE AREA
BEGINNING SATURDAY EVENING...BUT CONFIDENCE IS VERY LOW AT THIS
POINT AS THERE IS MUCH DISAGREEMENT IN THE MODELS.

&&

.AVIATION /04Z SUNDAY THROUGH THURSDAY/...
VFR CONDITIONS BECOME MVFR LATE TONIGHT. SNOW/IFR IS EXPECTED TO
SPREAD NORTH ACROSS THE TERMINALS SUNDAY MORNING BEFORE CHANGING
TO PL IN THE AFTERNOON...THEN FZRA SUNDAY EVENING. FZRA WILL
CONTINUE THROUGH SUNDAY NIGHT FOR CHO-MRB-IAD. LOWER CONFIDENCE IN
CONSTANT FZRA FOR BWI-MTN-DCA DUE TO TEMPS NEAR FRZG MVFR/IFR
CONDITIONS ARE POSSIBLE DURING THIS TIME.

HIGH PRESSURE MOVES INTO THE REGION TUESDAY AND CONTINUES THROUGH
THE MIDDLE OF THE WEEK.

&&

.MARINE...
SMALL CRAFT ADVISORY IN EFFECT FOR ALL BUT THE WESTERN TRIBUTARIES
TONIGHT FOR 20 KT NLY GUSTS. WENT SCA FOR MD WATERS SOUTH OF SANDY
POINT FOR SUNDAY FOR CONTINUED NORTH WINDS.

SNOW/RAIN EXPECTED SUNDAY MORNING BEFORE CHANGING OVER A MIX OF
FZRA-SLEET-MORE RAIN SUNDAY AFTERNOON. NLY WNDS WL VEER NELY
SUN...AND ELY SUN NGT. SPDS SHUD BE AOB 10 KT.

CHANNELING OF NORTHERLY WINDS COULD LEAD TO GUSTY CONDITIONS
NECESSITATING A SMALL CRAFT ADVISORY FOR AT LEAST THE MIDDLE
CHESAPEAKE BAY OVERNIGHT TUESDAY AND OVERNGT THURSDAY.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
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DC...WINTER WEATHER ADVISORY FROM 8 AM SUNDAY TO 7 AM EST MONDAY
     FOR DCZ001.
MD...WINTER STORM WARNING FROM 8 AM SUNDAY TO 10 AM EST MONDAY FOR
     MDZ003>006-009-010-502.
     WINTER WEATHER ADVISORY FROM 8 AM SUNDAY TO 7 AM EST MONDAY
     FOR MDZ007-011-013-014-016.
     WINTER WEATHER ADVISORY FROM 10 AM SUNDAY TO 10 AM EST MONDAY
     FOR MDZ501.
     WINTER WEATHER ADVISORY FROM 8 AM TO 8 PM EST SUNDAY FOR
     MDZ017-018.
VA...WINTER STORM WARNING FROM 8 AM SUNDAY TO 10 AM EST MONDAY FOR
     VAZ025>031-036>040-042-050>053-501>504.
     WINTER WEATHER ADVISORY FROM 8 AM SUNDAY TO 7 AM EST MONDAY
     FOR VAZ054>057.
WV...WINTER STORM WARNING FROM 8 AM SUNDAY TO 10 AM EST MONDAY FOR
     WVZ050>053-055-502-504>506.
     WINTER WEATHER ADVISORY FROM 10 AM SUNDAY TO 10 AM EST MONDAY
     FOR WVZ501-503.
MARINE...SMALL CRAFT ADVISORY UNTIL 6 PM EST SUNDAY FOR ANZ532>534-537-
     540-541-543.
     SMALL CRAFT ADVISORY UNTIL 6 AM EST SUNDAY FOR ANZ530-531-539.
-- End Changed Discussion --

&&

$$
UPDATE...JACKSON
PREVIOUS...ABW/KLW/CEB