Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 170941
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
441 AM EST WED DEC 17 2014

.SYNOPSIS...
A TROUGH SWINGS THROUGH TODAY WITH HIGH PRESSURE BUILDING IN FOR THE
SECOND HALF OF THE WEEK. A WEAK WAVE OF LOW PRESSURE WILL CROSS
THE AREA SATURDAY NIGHT.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
COUPLE ISSUES STILL OF CONCERN FOR THIS MORNING AS INITIAL COLD
FRONT SWINGS OFF TO THE EAST AND SECONDARY TROUGH MOVES THROUGH
LATER THIS MORNING. DESPITE THE WESTERLY WIND SHIFT WITH THE
FRONTAL PASSAGE EARLIER TONIGHT...WINDS REMAINING LIGHT ACROSS
MUCH OF THE EASTERN AREA. THIS COMBINED WITH A STILL MOISTURE
THICK ENVIRONMENT AS THE DRIER AIR HAS YET TO MOVE IN HAS RESULTED
IN THE WIDESPREAD FOG. GUIDANCE ALL OVER THE PLACE IN TRYING TO
CAPTURE THE REDUCED VIS WITH THE FOG FORMATION...BUT THINKING WILL
SEE CLEARING WEST TO EAST AS TROUGH PIVOTS THROUGH...INCREASING
WINDS AND USHERING IN THE DRIER AIR. DENSE FOG ALREADY DISSIPATING
ACROSS NORTHERN CENTRAL MD COUNTIES VIA 09Z OBS. HAVE THUS CANCELLED
THE DENSE FOG ADV THERE TO ACCOUNT FOR THIS. THE DENSE FOG ADV
REMAINS IN EFFECT FOR PORTIONS OF NORTHERN VA AND CENTRAL
MD...HOWEVER LATEST THINKING LOOKS LIKE THE ADV WILL MOST LIKELY
BE CANCELLED PRIOR TO THE 13Z END TIME AS CONDITIONS ARE GENERALLY
ON THE IMPROVING TRACK.

SECOND CONCERN IS PCPN FOR THE AREAS WEST OF THE ALLEGHENY FRONT.
09Z RADAR IMAGERY AND OBS INDICATING LIGHT PCPN ASSOCIATED WITH
THE TROUGH AND WEAK SHORTWAVE POSITIONED OVER WESTERN WV/PA.
INCREASING WESTERLY FLOW SHOULD WORK TO GENERATE SCT UPSLOPE
SHOWERS...WITH THE BEST CHC THIS MORNING...THEN TAPERING OFF
DURING THE AFTN. COLD AIR HAS BEEN SLOW TO MOVE IN...AND AS SUCH
CAN EXPECT MIX RAIN/SNOW SHOWERS...WITH ALL SNOW AT THE HIGHEST
ELEVATIONS. THE PCPN IS VERY LIGHT IN NATURE...AND ONLY A COUPLE
TENTHS OF AN INCH OF SNOW AT MOST IS FORECASTED.

FOR TEMPS TODAY...CAA FAIRLY WEAK AS TROUGH ALOFT TURNS MORE
ZONAL...KEEPING THE COLDER TEMPS TO THE NORTH. THE BETTER SHOT OF
CAA NOT EXPECTED TILL TONIGHT. SIDED MORE WITH A WARMER MAV SOLUTION
AS DOWNSLOPING COMPONENT FOR MOST OF THE CWA WITH SKIES SCATTERING
OUT SEEMS THE MORE REASONABLE SOLUTION.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH THURSDAY NIGHT/...
HIGH PRESSURE BEGINS TO BUILD IN FROM THE WEST TONIGHT THROUGH
THURSDAY...WITH THE AREA REMAINING ON THE WESTERN PERIPHERY DURING
THIS TIME. ZONAL FLOW ALOFT WILL WEAKEN TONIGHT AS A TROUGH PIVOTS
THROUGH...FOLLOWED BY A STRONGER SHORTWAVE TOMORROW. OVERALL
EXPECTING DRY CONDITIONS THOUGH FOR MOST OF THE AREA EXCEPT WEST OF
THE ALLEGHENY FRONT WHICH COULD SEE FLURRIES THIS EVENING. DESPITE
DECENT FORCING ALOFT WITH THE MULTIPLE SHORTWAVES DURING THIS
PERIOD...LACK OF MOISTURE WILL KEEP ANYTHING FROM FORMING...WITH THE
ONLY IMPACT FROM THE ENERGY THUS BEING INCREASED CLOUD COVER.

THE STRONGER CAA FINALLY DIPS SOUTH TONIGHT...WITH OVERNIGHT LOWS
TONIGHT AND TOMORROW DROPPING TO NEAR NORMAL LEVELS. SIDED MORE WITH
THE MET FOR LOWS AND CONTINUED WITH THE TREND OF LEANING TO THE MAV
FOR THE HIGHS ON THURSDAY.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
RDGG OVER CWFA SFC UP THRU H5 FRI-FRI NGT. THUS KEPT BOTH PDS DRY.
SHUD HV PLENTY OF SUN DURING THE DAY. MSTR INCREASES FM THE SW AT
NGT...SPCLY AFTR MIDNGT. WL HV SKIES BCMG MOCLDY IN VA...NE OF PTMC
RIVER MAY AVG OUT PTCLDY.

GDNC CONTINUING TO CONVERGE ON A SOLUTION THRU THE WKND...WHICH
TAKES AN OPEN SRN STREAM WV WELL SOUTH OF THE CWFA SAT. LTST ECMWF
MUCH LESS DVLPD WRT CSTL LOW. NONETHELESS...THIS TRACK...AND A NRN
STREAM S/WV...WL BE SUFFICIENT TO TOSS LGT PCPN THIS WAY. COLD AIR
WL BE MARGINAL AT BEST...SUGGESTING THERE MAY BE A DIURNAL AND ELEV
COMPONENT TO PTYPE. STILL HV SNOWY/MIXED PDS...SPCLY W OF THE I-95
CRRDR. THE WETTEST PD MAY TURN OUT TO BE SAT NGT...WHICH WUD BE ABT
WHEN LOW WL TRANSFER ITS ENERGY TO THE COAST...AND WE/LL ALSO HV PVA
ALOFT. AM KEEPING SCHC/CHC POPS INTO SUNDAY...MORE OUT OF RESPECT TO
ECMWF...AND THE TIMING/STRENGTH DIFFS THAT LINGER.

SUBSIDENCE BLDS BHD THIS SYSTEM FOR SUN NGT-MON NGT. H5 FLOW STILL
QUITE ZNL...SO THERE WONT BE A LOT OF COLD AIR AVBL. HV TEMPS ONLY A
CPL DEGF BLO AVG. THERE MAY BE YET ANOTHER STORM SYSTEM ON THE
HORIZON BY DAY 7. WL BE GENERIC ATTM...AS THERE/S A LOT OF WX TO GET
THROUGH FIRST.

&&

.AVIATION /10Z WEDNESDAY THROUGH SUNDAY/...
ALL TAF SITES ON THE IMPROVING TRACK THIS MORNING AS KIAD AND KDCA
HAVE BOTH INCREASED TO MVFR. VFR CONDITIONS FOR THE REMAINING
SITES. SHOULD SEE VFR CONDITIONS AT KIAD AND KDCA BY 12Z WITH VFR
THEN IN PLACE DURING THE DAY TODAY.

LIGHT FLOW EARLY THIS MORNING WILL INCREASE FROM THE WEST AFTER
DAYBREAK...WITH GUSTS AROUND 20-25 KTS MIXING IN BETWEEN 14-16Z.
GUSTS END BY 00Z TONIGHT...WITH W FLOW CONTINUING
OVERNIGHT...GENERALLY LESS THAN 10 KTS. OCNL GUSTS PSBL KDCA
OVERNIGHT...BUT NOT ENOUGH CONFIDENCE TO INCLUDE IN TAF.

VFR CONDITIONS TONIGHT THROUGH THURSDAY.

VFR FRI-FRI NGT. FLGT RESTRICTIONS SHUD OVERSPREAD TERMINALS SAT...
AND LINGER INTO ELY SUN. PCPN MAY BE ON THE LGT SIDE...WHICH WUD
SUGGEST THAT MVFR MAY PREVAIL...W/ PDS OF IFR. PTYPE STILL IN QSTN.

&&

.MARINE...
SCA IN EFFECT FOR TODAY FOR ALL WATERS WITH INCREASING WEST
WINDS...GUSTING UP TO 20 KTS. THE SCA REMAINS IN EFFECT THROUGH
TONIGHT AND THROUGH THURSDAY. THERE COULD BE PERIODS TONIGHT WHERE
THE WINDS DROP BELOW 18 KTS...BUT THE WINDOW SMALL ENOUGH TO WARRANT
THE CONTINUATION OF THE SCA. THE SCA REMAINS ON ALL WATERS THURSDAY
MORNING...THEN WITH HIGHER CONFIDENCE OF THE GUSTS REMAINING ABV 18
KTS OVER JUST THE NORTHERN CHESAPEAKE BAY MAINTAIN THE SCA THERE
TILL THURS EVENING.

HIPRES OVER THE WATERS FRI. WK LOPRES PASSING WELL S OVER THE WKND.
WHILE PCPN XPCTD TO REACH WATERS...THE GRADIENT SHUD BE ON THE LGT
SIDE. FOR THAT REASON...NO FLAGS XPCTD ATTM.

&&

.TIDES/COASTAL FLOODING...
WATER LEVEL DEPARTURES DOWN TO A FOOT OR SLIGHTLY LESS. THAT TREND
SHOULD CONTINUE FOR THE NEXT DAY OR TWO.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...DENSE FOG ADVISORY UNTIL 8 AM EST THIS MORNING FOR MDZ503-504.
VA...DENSE FOG ADVISORY UNTIL 8 AM EST THIS MORNING FOR VAZ040-
     051>053-501-502-505-506.
WV...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 9 AM THIS MORNING TO 6 PM EST
     THURSDAY FOR ANZ530>532-538>540.
     SMALL CRAFT ADVISORY FROM 9 AM THIS MORNING TO 1 PM EST
     THURSDAY FOR ANZ533>537-541>543.

&&

$$
SYNOPSIS...SEARS/HTS
NEAR TERM...SEARS
SHORT TERM...SEARS
LONG TERM...HTS
AVIATION...SEARS/HTS
MARINE...SEARS/HTS
TIDES/COASTAL FLOODING...HTS






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