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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KLWX 060254
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
954 PM EST THU DEC 5 2013

.SYNOPSIS...
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A COLD FRONT WILL MOVE INTO THE AREA TONIGHT AND FRIDAY MORNING.
HIGH PRESSURE WILL BUILD OVERHEAD SATURDAY. LOW PRESSURE WILL
IMPACT THE AREA SUNDAY INTO MONDAY. CANADIAN HIGH PRESSURE WILL
RETURN FOR THE MIDDLE OF NEXT WEEK.
-- End Changed Discussion --

&&

.NEAR TERM /THROUGH FRIDAY/...
-- Changed Discussion --
SFC COLD FRONT IS LOCATED OVER THE APPALACHIANS. SLY FLOW IN
PRE-FRONTAL WARM SECTOR HAS YIELDED A VERY MILD NIGHT FOR DEC. TEMPS
AT 9 PM ACROSS THE CWA RANGE FROM THE MID 50S TO THE MID 60S. THE
COLD FRONT WILL MOVE THRU THE POTOMAC HIGHLANDS LATE THIS EVE...AND
GRADUALLY PUSH SEWD TOWARD I-95 TOWARD DAWN. NW WINDS WILL BE
ACCOMPANIED BY A DROP IN TEMPS BEHIND THE FRONT WHILE TEMPS WILL
REMAIN MILD AHEAD OF THE FRONT. MIN TEMP FCST IS TRICKY IN THE SETUP
AS IT IS HIGHLY DEPENDENT ON THE POSITION OF THE FRONT BY MRNG.

ADJUSTED POPS BASED OFF RECENT RADAR TRENDS AND HRRR GUIDANCE...
WHICH HAD ACCURATELY CAPTURED THE RECENT WEAKENING TREND OF PRECIP
AHEAD OF THE FRONT AS THIS ACTIVITY CROSS THE MTS. SHOWERS THIS EVE
WILL BE VERY LIGHT AND INTERMITTENT. PRECIP SHOULD MAINLY BE LGT
OVNGT BUT HIGHER IN COVERAGE WHEN THE FROPA MOVES THRU.

THE COLD FRONT WILL SAG SWD INTO CENTRAL VA/SRN MD IN THE MRNG AND
SRN VA BY THE AFTN. FCST TEMPS DO NOT FOLLOW A DIURNAL CURVE WITH
CAA OCCURRING IN POST-FRONTAL SECTOR. THEREFORE...HIGHS WILL LIKELY
OCCUR AROUND MIDNIGHT BEFORE DROPPING IMMEDIATELY BEHIND THE FRONT
AND REMAINING STEADY IN THE AFTN. THE ANA-FRONTAL STRUCTURE OF THIS
SYSTEM WILL TRANSLATE TO A WET DAY ON FRI. MODELS CONTINUE TO SHOW
THE BEST FORCING ALONG AND ON THE COLD SIDE OF THE H8 BAROCLINIC
ZONE. MODELS ARE IN GOOD AGREEMENT WITH THE AXIS OF HEAVIER AND
STEADIER PRECIP CLOSER TOWARD THE MASON-DIXON LINE AND ALLEGHENY
FRONT. QPF AMOUNTS THRU FRI AFTN RANGE FROM LESS THAN A QUARTER INCH
S/E OF I-95 TO JUST UNDER AN INCH ALONG THE ALLEGHENY FRONT.
-- End Changed Discussion --

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY/...
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THE COLD FRONT - WHICH WL BE CAUGHT UP IN THE SW-NE RUNNING
JET...WL SLOWLY SLIDE THRU THE MID ATLC FRI NGT. FRI NGT WL BE
WET...BUT P-TYPE WL BE LIQUID OUTSIDE OF THE HIGHER ELEVS. PCPN WL
BE EXITING THE RGN BY SAT MRNG. FCST SNOWFALL ACCUMULATIONS ALONG
THE ALLEGHENY FRONT ARE UNDER AN INCH. TEMPS WL RANGE FM THE 20S
IN THE HIGHLANDS TO THE L40S ALONG THE BAY...30S ELSEWHERE.

SAT WL DFNTLY BE THE NICER DAY OF THE WKND AS HIGH PRES MOVES OVER
THE RGN. HIGHS IN THE 30S AND L40S.
-- End Changed Discussion --

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
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SUNDAY`S MET PATTERN IS COMPLEX. THE HIGH WHICH WAS OVR THE RGN
SAT WL BE TRACKING NE OVR LONG ISLAND. AT SAME TIME LOW PRES IS
PROGGED TO FORM ON THE TAIL END OF THE BNDRY WHICH CAME THRU FRI
NGT. THIS IS GOING TO PLACE THE MID ALTC RGN IN THE CLASSIC CAD
SITUATION W/ ISOTHERMS/ISOBARS KINKING DOWN THE ERN SIDE OF THE
APLCHNS.

PCPN LKLY TO BEGIN SUN MRNG AS A PD OF SNOW...BCMG A WINTRY MIX
BY SUN AFTN. WE ARE STILL 3 DAYS OUT...SO I AM HESITANT TO TRY TO
PIN DOWN EXACTLY WHAT I THINK WL HAPPEN...BUT FZRA/IP ARE XPCTD W
OF I-95 SUN AFTN/EVE. ALONG THE BAY THE WATER TEMP IS STILL IN THE
L40S...W/ ERLY FLOW BLV PCPN CLOSE TO THE WATER WL BE RA SUN AFTN.
IN THE CITIES/ALONG I-95 COULD BE RA OR ZR DEPENDING ON THE
ATMOSPHERIC TEMP PROFILE. IN THE MAJOR CITIES TEMPS WL PRBLY BE
CLOSE TO FRZG...SO EVEN IF P-TYPE IS FZRA ACCUMULATING FZRA WL
PRBLY BE DIFFICULT. W OF I-95 COULD A DIFFERENT STORY...BUT THERE
ARE STILL MULTIPLE MDL RUNS TO COME IN OVR THE NEXT 48-60 HRS.
ADJUSTMENTS WL LKLY HV TO BE MADE TO THIS FCST.

CSTL LOW XPCTD TO DVLP NEAR ORF SUN NGT...KEEPING THE MID ATLC
WET. THE CAD PATTERN IS ALSO XPCTD TO CONT...WHICH WOULD LEAD TO
PROLONGING THE WINTRY WX. A MIX IS XPCTD. LOWS IN THE L30S XCPT
WARMER ALONG BAY.

HIGH PRES FINALLY BLDS BACK INTO THE RGN TUE...BUT THIS WL LKLY
LEAD TO A BRZY/WINDY DAY.
-- End Changed Discussion --

&&

.AVIATION /03Z FRIDAY THROUGH TUESDAY/...
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PERIODS OF LGT RAIN ARE EXPECTED THRU THE NGT AS A COLD FRONT
MOVES THRU THE TERMINALS. EXPECT FROPA TO OCCUR FROM WEST TO EAST
BETWEEN OVNGT AT MRB AND ERY TO MID FRI MRNG FARTHER SOUTH AND
EAST. SLY WINDS AND MAINLY MVFR VSBYS AHEAD OF THE FRONT BECOME
NWLY WITH CIGS LOWERING TO BORDERLINE MVFR-IFR BEHIND THE FRONT.

MORE WIDESPREAD RAIN WILL ENTER THE REGION FRIDAY AS LOW PRESSURE
FORMS ALONG THE FRONTAL BOUNDARY. LOW CONFIDENCE IN CIGS IMPROVING
TO MVFR/VFR DUE TO THE SLOW NATURE OF THE FRONT AND DEVELOPING LOW
PRESSURE.

FRI NGT RA/LOW CIGS/FOG PSBL AT ALL TAF SITES...THEN IMPRVG SAT AS
HIGH PRES BLDS OVR THE RGN. SUN/SUN NGT COULD BE POOR AT ALL TAF
SITES AS LOW CIGS/POOR VSBY/WINTRY PCPN XPCTD. HIGH PRES FINALLY
BUILDS BACK INTO THE MID ATLC TUE....WHICH SHOULD CREATE GUSTY W WINDS.
-- End Changed Discussion --

&&

.MARINE...
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SLY CHANNELING IN THE MAIN STEM OF THE CHSPK BAY HAVE PRODUCED
WIND GUSTS AROUND 15 KT. DELAYED ONSET OF SCA ELSEHWERE UNTIL LATE
TNGT. A WARM AIRMASS ATOP COLD WATER DOES NOT PRODUCE A FAVORABLE
SETUP FOR MIXING...SO AM ON THE FENCE OF CANCELLING SCA FOR AREAS
THAT ARE NOT PRONE TO SLY CHANNELING.

SCA ISSUED FOR LATE FRI NGT AS A COLD FRONT MOVES SOUTH OF THE
WATERS AND THE PRESSURE GRADIENT INCREASES. NLY GUSTS 20-25 KT WILL
ACCOMPANY THIS PRESSURE SURGE. SCA WILL LIKELY NEED TO BE EXTENDED
INTO SAT.

WINDS MAY DECREASE SUNDAY AS HIGH PRESSURE PASSES TO OUR NORTH...THEN
INCREASE TO AT LEAST MARGINAL CONDITIONS AGAIN MONDAY AS A COLD
FRONT APPROACHES. A MORE SIGNIFICANT SCA...PSBLY GALE IS PSBL TUE
AS HIGH PRES BLDS BACK INTO THE WATERS.
-- End Changed Discussion --

&&

.HYDROLOGY...
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AN UNSETTLED WEATHER PERIOD IS IN STORE FOR THE MID-ATLANTIC REGION.
FORECAST RAINFALL AMOUNTS THRU FRI NGT ARE LOWER THAN PREVIOUSLY
EXPECTED...GENERALLY ON THE ORDER OF 0.50-1 INCH...WHICH CREATES
ONLY MINOR RISES IN RIVERS.

HOWEVER...MORE PRECIPITATION IS PROJECTED OVER THE REGION SUNDAY
INTO MONDAY...AND THIS WILL LIKELY BE HEAVIER THAN THE FIRST ROUND.
GFS ENSEMBLE MEAN RAINFALL FOR BOTH EVENTS COMBINED IS CLOSE TO
THREE INCHES...WITH SOME MEMBERS SHOWING OVER 4 INCHES. GIVEN
LITTLE RECOVERY TIME IN BETWEEN EVENTS...THIS AMOUNT OF
RAINFALL...IF IT OCCURS...COULD BE SUFFICIENT TO GENERATE FLOODING
ON BOTH SMALL STREAMS AND ON THE MAINSTEM RIVERS SUNDAY THROUGH
EARLY NEXT WEEK. IF FROZEN PRECIP FALLS...THE MELTING OF IT FACTORS
INTO THE EQUATION TOO. THERE IS STILL A GREAT DEAL OF UNCERTAINTY
REGARDING WHERE THE HEAVIEST PRECIPITATION SETS UP...AND WHETHER IT
STAYS IN ONE PLACE FOR A WHILE. THIS SITUATION WILL CONTINUE TO BE
MONITORED IN THE DAYS AHEAD.
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&&

.TIDES/COASTAL FLOODING...
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ANOMALIES REMAIN STEADY AROUND 3/4 FOOT ABOVE. NO COASTAL FLOODING
IS EXPECTED TNGT...AND WINDS WILL SHIFT TO THE NORTHWEST BEHIND A
COLD FRONT LATER FRIDAY THROUGH FRIDAY NIGHT. WATERS LEVELS WILL
DECREASE DURING THIS TIME. HAVE REMOVED THREAT OF COASTAL FLOODING
OUT OF THE HWO.
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&&

.LWX WATCHES/WARNINGS/ADVISORIES...
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DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 1 PM EST FRIDAY FOR ANZ531>534-537-
     539>541-543.
     SMALL CRAFT ADVISORY FROM MIDNIGHT FRIDAY NIGHT TO 6 AM EST
     SATURDAY FOR ANZ530>543.
     SMALL CRAFT ADVISORY UNTIL 1 PM EST FRIDAY FOR ANZ530-535-536-
     538-542.
-- End Changed Discussion --

&&

$$
UPDATE...JRK
PREV FCST...HAS/WOODY!