Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 170846
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
346 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 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 STILL 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...WITH AREAS OF DENSE FOG. AS SUCH...WITH ON GOING DENSE FOG
ACROSS CENTRAL MD/NORTHERN VA...MAINLY SANDWICHED BETWEEN THE
BALTIMORE/DC METRO AREAS AND THE BLUE RIDGE...HAVE DENSE FOG ADV IN
EFFECT FOR THIS AREA THRU 13Z. PATCHY FOG PSBL IN REMAINING AREAS
THRU AT LEAST DAYBREAK. 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. DEPENDENT UPON TIMING...COULD
VERY WELL END UP SEEING THE ADV ENDING BEFORE 13Z.

SECOND CONCERN IS PCPN FOR THE AREAS WEST OF THE ALLEGHENY FRONT.
08Z 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 /09Z WEDNESDAY THROUGH SUNDAY/...
ON GOING IFR OR LOWER CONDITIONS AT KIAD AND KDCA THIS
MORNING...WITH THE REMAINING AREA MVFR OR HIGHER. MODERATE
CONFIDENCE FOR THE NON IFR LOCATIONS STAYING ABV IFR. LOW CONFIDENCE
ON IMPROVEMENT TIME AT KIAD...THOUGH GUIDANCE INDICATES DIMINISHED
VIS/CIGS THRU AT LEAST 12Z. KDCA SHOULD SEE IMPROVING CIGS BY 14Z.

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 MDZ004>006-
     503>506.
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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