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000
FXUS61 KLWX 060829
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
329 AM EST FRI DEC 6 2013

.SYNOPSIS...
A COLD FRONT WILL PASS THROUGH THE AREA THIS MORNING. A WAVE OF LOW
PRESSURE WILL DEVELOP ALONG THE FRONT...BRINGING UNSETTLED
CONDITIONS THROUGH TONIGHT. HIGH PRESSURE WILL BUILD OVERHEAD
SATURDAY...BUT LOW PRESSURE WILL IMPACT THE AREA SUNDAY INTO MONDAY
WITH WINTRY PRECIPITATION. AN UPPER-LEVEL DISTURBANCE WILL PASS
THROUGH THE AREA TUESDAY AND CANADIAN HIGH PRESSURE WILL BUILD
OVERHEAD DURING THE MIDDLE OF NEXT WEEK.
&&

.NEAR TERM /THROUGH TONIGHT/...
CURRENT ANALYSIS SHOWS A COLD FRONT MOVING INTO THE AREA FROM THE
NORTH EARLY THIS MORNING. A SOUTHERLY FLOW AHEAD OF THE FRONT
HAS ALLOWED FOR UNUSUALLY MILD CONDITIONS FOR THIS TIME OF YEAR.
HOWEVER...TEMPERATURES BEHIND THE FRONT ARE DROPPING QUICKLY.

THE COLD FRONT WILL CONTINUE TO DROP SOUTH THROUGH THE CWA THIS
MORNING. THE COLD FRONT WILL LIKELY CROSS THE CITIES OF WASHINGTON
AND BALTIMORE BEFORE SUNRISE BEFORE WORKING ITS WAY THROUGH CENTRAL
VIRGINIA BY MID-MORNING. NORTHERLY WINDS BEHIND THE FRONT WILL CAUSE
TEMPERATURES TO DROP QUICKLY INTO THE 40S...WITH 30S EXPECTED OVER
THE MOUNTAINS.

SHORTWAVE ENERGY IN THE SOUTHWEST FLOW ALOFT WILL COMBINE WITH WARM
AIR OVERRUNNING THE SHALLOW COLD AIR MOVING IN PLACE...RESULTING IN
PERIODS OF RAIN TODAY. THE STEADIEST RAIN WILL BE ACROSS THE
NORTHWESTERN PORTION OF THE CWA...CLOSER TO THE SHORTWAVE ENERGY AND
THE 850MB FRONT.

A WAVE OF LOW PRESSURE WILL DEVELOP ALONG THE FRONT THIS EVENING
BEFORE EVENTUALLY PASSING OFF TO OUR SOUTHEAST LATE TONIGHT. MORE
RAIN IS EXPECTED ACROSS THE ENTIRE AREA. A SOAKING RAIN IS EXPECTED
WITH RAINFALL AMOUNTS THROUGH TONIGHT RANGING FROM ONE HALF TO ONE
INCH ACROSS MOST AREAS...BUT OVER ONE INCH ACROSS PORTIONS OF THE
POTOMAC HIGHLANDS. A DRY NORTHWEST FLOW WILL WORK ITS WAY INTO THE
AREA AFTER MIDNIGHT...CAUSING PRECIPITATION TO TAPER OFF DURING THIS
TIME.

WILL CONTINUE TO WATCH LOW-LEVEL COLD AIR MOVING IN PLACE LATER THIS
AFTERNOON THROUGH TONIGHT. THERE WILL BE A LAYER OF BELOW FREEZING
TEMPS THAT MAY MOVE INTO PORTIONS OF THE ALLEGHENY HIGHLANDS DURING
THIS TIME. WITH WARM AIR ALOFT...THAT MAY CAUSE A PERIOD OF FREEZING
RAIN ACROSS THESE AREAS. THE BEST CHANCE FOR THAT TO HAPPEN WILL BE
THIS AFTERNOON AND EVENING. PRECIPITATION WILL END AS A LITTLE SNOW
AND SLEET AFTER MIDNIGHT...BUT SNOW AND SLEET ACCUMULATION WILL BE
LIGHT. HAVE NOT ISSUED AN ADVISORY AT THIS TIME SINCE IT WILL BE
MARGINAL AND CONFINED TO A SMALL LAYER BETWEEN AROUND 1000 AND 3000
FEET ABOVE SEA LEVEL. WILL HAVE TO MONITOR TEMPERATURES UPSTREAM
THROUGHOUT THE DAY TO SEE IF A WINTER WEATHER ADVISORY IS
WARRANTED.
&&

.SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/...
CANADIAN HIGH PRESSURE WILL BUILD TOWARD THE REGION AS THE COLD
FRONT CONTINUES TO MOVE WAY OFF TO OUR SOUTH AND EAST. A DRY
NORTHWEST FLOW WILL CONTINUE TO USHER IN DRIER CONDITIONS ALONG WITH
SOME SUNSHINE. ANY LEFTOVER SNOW SHOWERS ALONG THE ALLEGHENY
HIGHLANDS SHOULD END DURING THE MORNING AND ANY LEFTOVER SHOWERS
ACROSS EXTREME SOUTHERN MARYLAND WILL ALSO DISSIPATE DURING THE
MORNING.

DESPITE DRY CONDITIONS AND INCREASING SUNSHINE...TEMPERATURES WILL
BE MUCH COLDER COMPARED TO RECENT DAYS DUE TO THE COLD NORTHWEST
FLOW. MAX TEMPS WILL RANGE FROM THE UPPER 20S IN THE MOUNTAINS TO
THE LOWER AND MIDDLE 40S IN CENTRAL VIRGINIA.

CANADIAN HIGH PRESSURE WILL SETTLE OVERHEAD SATURDAY NIGHT...CAUSING
COLD CONDITIONS. MIN TEMPS WILL BE IN THE 20S ACROSS MOST AREAS. A
STORM SYSTEM WILL MOVE OUT OF THE ROCKIES INTO THE CENTRAL CONUS
SATURDAY NIGHT. HIGH AND MID-LEVEL CLOUDS WILL INCREASE AHEAD OF
THIS SYSTEM. A SOUTHWEST FLOW ALOFT AHEAD OF THIS SYSTEM WILL
CAUSE PLENTY OF WARM AND MOIST AIR FROM THE GULF OF MEXICO TO
OVERRUN THE LOW-LEVEL COLD AIR IN PLACE. THIS WILL CAUSE
PRECIPITATION TO BREAK OUT OVER THE TENNESSEE VALLEY SATURDAY NIGHT.
THIS PRECIPITATION WILL SPREAD TO OUR SOUTHWESTERN AREAS TOWARD DAY
BREAK. TEMPERATURES WILL BE COLD ENOUGH TO SUPPORT SNOW...AND SNOW
MAY BEGIN TOWARD SUNRISE ACROSS PORTIONS OF CENTRAL VIRGINIA.
ELSEWHERE...WINTRY PRECIPITATION WILL LIKELY HOLD OFF UNTIL SUNDAY.
&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
SUN-MON STILL LOOKING LIKE A COMPLICATED FCST...BUT HGT FIELDS
DEPICTING REMARKABLE AGREEMENT IN OVERALL PTTN. THERMAL PTTN H9-7
STILL A BIT UNCERTAIN...WHICH WL BE THE KEY TO THIS FCST.

THE DAY WL START SUNDAY W/ A HIPRES RDG /SFC PRES 1036 MB/ OVER
NY/PA...SUPPLYING PLENTY OF LLVL COLD AIR. WAA WL GET CRANKING ACRS
THE MS/OH VLYS...PROVIDING A WARM AIR INTRUSION-- THE DEPTH AND
EXTENT OF WHICH STILL TBD. AM THINKING THAT EVAP COOLING WL ASSIST
IN STARTING PCPN AS SNOW...EVENTUALLY MIXING W/ PL/FZRA. AS SFC RDG
BECOMES ENTRENCHED ALONG THE APLCHNS AND WAA CONTS H9-7...PCPN WL
BECOME INCRSGLY FZRA BASED...CHGG OVER TO RA AS THE MARINE INFLUENCE
STRENGTHENS. AM NOT WILLING TO SPECIFICALLY TIME TRANSITIONS AS
DRIVING FORCES SUBTLE...AND STILL SUBJECT TO CHG. THERE ARE NO SGFNT
SYNOP FEATURES INVOLVED ASIDE FM SFC HIPRES...PURELY MID-UPR LVL
DYNAMICS. REGARDLESS OF SPECIFICS...THE SUNDAY INTO ELY MON PD
LOOKING MESSY. ALL INTERESTS SHUD MONITOR FUTURE FCSTS. AS THE WV OF
PCPN EXITS MON...THE GNRL THEME SHUD PT TO MAINLY RAIN AS TEMPS DO
GET ABV FRZG.

GFS/ECMWF PART WAYS AT THIS POINT. EURO PLACING GREATER EMPHASIS ON
COLD SFC HIGH...GFS LEADING TWD ANTHR WV RIDING ALNG STALLED BNDRY
TUE. VORT DROPPING INTO GRTLKS SHUD BUMP BNDRY EWD A BIT...AND
THEREFORE WL BE LEANING FCST ON THE DRIER SIDE. WUD CONSIDER XTNDD
FCST CONFIDENCE A LTL LOW BASED ON THIS SPREAD.
&&

.AVIATION /08Z FRIDAY THROUGH TUESDAY/...
MOSTLY MVFR CIGS ARE EXPECTED EARLY THIS MORNING...BUT THERE MAY BE
A PERIOD OF IFR CONDITIONS AS A COLD FRONT PASSES THROUGH DURING
THIS TIME. CIGS WILL LIKELY IMPROVE TO MVFR LEVELS FOR MOST OF
TODAY...BUT THERE WILL BE PERIODS OF RAIN.

RAIN WILL CONTINUE FOR MOST OF TONIGHT AND CIGS MAY DROP TO IFR
LEVELS LATE THIS AFTERNOON THROUGH MUCH OF TONIGHT AS A WAVE OF LOW
PRESSURE PASSES BY TO THE SOUTH. NORTH-NORTHWEST WINDS WILL DRY
THINGS OUT LATE TONIGHT INTO SATURDAY MORNING...CAUSING CIGS TO
IMPROVE TO VFR LEVELS DURING THIS TIME. VFR CONDITIONS WILL PERSIST
SATURDAY NIGHT.

NORTH-NORTHWEST WINDS WILL GUST AROUND 20 KNOTS FOR A FEW HOURS
BEHIND THE FRONT THIS MORNING...BUT A WEAKER GRADIENT WILL CAUSE
GUSTY WINDS TO DIMINISH FOR THIS AFTERNOON AND EVENING. ANOTHER
PRESSURE SURGE IS EXPECTED BEHIND THE WAVE OF LOW PRESSURE LATE
TONIGHT THROUGH SATURDAY AND NORTH-NORTHWEST WINDS WILL GUST AROUND
20 KNOTS. WINDS WILL DIMINISH SATURDAY NIGHT.

NMRS FLGT RESTRICTIONS SUN INTO MON IN WINTRY WX. PCPN SHUD START AS
SNW...THEN MIX/CHG TO PL/FZRA...AND EVENTUALLY RA. DCA/BWI/MTN WL
COMPLETE THE PROCESS QUICKEST...MRB WL BE THE SLOWEST. SOME OF THESE
RESTRICTIONS MAY LINGER INTO THE MON MRNG PUSH. ALTHO TEMPS WL
SLOWLY RISE ABV FRZG MON...STILL XPCTG LOW CIGS. GRDL IMPVMNT WL
COME MON NGT-TUE.
&&

.MARINE...
A COLD FRONT WILL PASS THROUGH THE WATERS THIS MORNING. A PRESSURE
SURGE BEHIND THE FRONT WILL CAUSE NORTH-NORTHWEST WINDS TO GUST
AROUND 20 KNOTS. A SMALL CRAFT ADVISORY REMAINS IN EFFECT.

A WAVE OF LOW PRESSURE WILL PASS BY TO THE SOUTH THIS EVENING AND
ANOTHER PRESSURE SURGE IS EXPECTED BEHIND THE WAVE LATE TONIGHT
THROUGH SATURDAY. A SMALL CRAFT ADVISORY IS IN EFFECT FOR THE WATERS
DURING THIS TIME. NORTH-NORTHWEST WINDS WILL CONTINUE SATURDAY NIGHT
AND A SMALL CRAFT ADVISORY MAY BE NEEDED FOR PORTIONS OF THE
MARYLAND CHESAPEAKE BAY AND LOWER TIDAL POTOMAC RIVER.

A PD OF WINTRY WX XPCTD SUN-SUN NGT. HWVR...WATER TEMPS SHUD ASSIST
IN TRANSITIONING PCPN TO RAIN...SPCLY ON THE OPEN WATERS OF THE BAY.
MIXING THRU THIS PD SHUD BE POOR. NLY WNDS WL GRDLY BECOME ELY...
GENLY AOB 10 KT. WNDS WL ATTEMPT TO VEER SELY ON MON...IT LKLY WL BE
A SLOW PROCESS.

AS THE STORM SYSTEM PROGRESSES INTO THE ATLC...WLY WNDS WL TAKE
HOLD. SHUD HV SOME GUSTY WNDS AT THAT PT.
&&

.HYDROLOGY...
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.

MORE PRECIPITATION IS PROJECTED OVER THE REGION SUNDAY INTO
MONDAY...AND THIS WILL LIKELY BE HEAVIER THAN THE FIRST ROUND.
NAEFS AND GEFS MEAN RAINFALL FOR BOTH EVENTS COMBINED IS BETWEEN
TWO AND THREE INCHES. WHILE THE LATEST MODELS HAVE BACKED OFF ON
QPF AND RIVER STAGE FORECASTS A BIT...THERE IS STILL A POTENTIAL
FOR SOME FLOODING ISSUES ON 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.
&&

.TIDES/COASTAL FLOODING...
TIDAL ANOMALIES REMAIN AROUND ONE HALF TO ONE FOOT ABOVE NORMAL THIS
MORNING. HOWEVER...NORTH-NORTHWEST WINDS BEHIND A COLD FRONT WILL
LIKELY CAUSE ANOMALIES TO DECREASE THIS AFTERNOON. THEREFORE...
COASTAL FLOODING IS NOT EXPECTED AT THIS TIME.
&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 1 PM EST THIS AFTERNOON FOR
     ANZ530>543.
     SMALL CRAFT ADVISORY FROM MIDNIGHT TONIGHT TO 6 PM EST
     SATURDAY FOR ANZ530>543.

&&

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