Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 300143
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
943 PM EDT SUN MAR 29 2015

.SYNOPSIS...
HIGH PRESSURE PUSHES OFFSHORE TONIGHT WITH A COLD FRONT CROSSING
THROUGH THE REGION ON MONDAY. A REINFORCING CLIPPER LOW WILL PASS
OVER THE REGION ON TUESDAY. THE HIGH PRESSURE THAT FOLLOWS WILL
SLIDE TO OUR SOUTHEAST THURSDAY AND FRIDAY ALLOWING FOR WARM
TEMPERATURES. ANOTHER COLD FRONT IS EXPECTED AT THE END OF THE
WEEK.

&&

.NEAR TERM /THROUGH MONDAY/...
01Z OBS HAS SFC HIGH TO THE SOUTH OFF THE CAROLINA COAST...WITH
APPROACHING FRONTAL SYSTEM BACK OVER OHIO. WITH THE HIGH
POSITIONED TO THE SOUTH...SOUTHERLY FLOW NOW OVER THE
AREA...WORKING TO INJECT IN MORE MOISTURE RICH AIR. A VERY DRY
AIRMASS NEEDS TO BE OVERCOME THOUGH...AS EVIDENT WITH DEW PTS
STILL HOVERING IN THE SINGLE DIGITS ACROSS MUCH OF THE AREA.
THINKING THE STRONGER SURGE OF MORE MOIST AIR...AS WELL AS WAA...WILL
COME WITH THE LLJ INCREASING AFTER MIDNIGHT TONIGHT...WITH SW
WINDS BETWEEN 40-50 KTS.

LOOKING UPSTREAM...THERE ARE A FEW SPOTS REPORTING LIGHT RAIN WITH
DEW PT DEPRESSIONS OF ALMOST 20. AS SUCH...HAVE VERY LIGHT RAIN
MENTIONED THRU 07Z FOR ONLY EXTREME WESTERN AREAS...THEN THINKING
WITH MORE MOISTURE ADVECTION SHOULD SEE THE AIRMASS SATURATE
ENOUGH FOR LIGHT RAIN TO OCCUR. TRICKY SITUATION WHEN RELATING TO
TEMPS...AS FORECASTED TEMPS HAVE DROPPED THIS EVENING...BUT ARE
EXPECTED TO REMAIN NEAR STEADY AROUND MIDNIGHT THEN INCREASE
TOWARD DAWN WITH THE WAA. DESPITE THE LOW DEW PTS...THE PCPN IS
EXPECTED TO REMAIN LIGHT ENOUGH SO NOT ANTICIPATING WET BULBING.
SO HAVE MAINLY LIGHT RAIN MENTIONED...WITH ISOLATED SPOTS THAT
COULD DROP TO THE LOWER 30S POTENTIALLY SEEING SOME SNOWFLAKES MIX
IN WITH THE RAIN. AFTER HAVING A DAY WITH HIGHS IN THE 40S AND
LOWER 50S...NOT ANTICIPATING SFCS TO DROP TO OR BELOW FREEZING FOR
LONG ENOUGH TO BE CONCERNED WITH ICE...ESP WITH ROAD TEMPS
CURRENTLY SHOWING IN THE 40S AND 50S (AS OF 01Z). THE EXCEPTION TO
THIS FORECAST WILL BE THE WESTERN SLOPES OF THE ALLEGHENIES WHICH
SHOULD SEE A PERIOD OF SNOW SHOWERS...AND PSBL UP TO A COUPLE
TENTHS OF AN INCH ACCUM.

THE FNT ITSELF WL BE RATHER MSTR STARVED. THEREFORE XPCT MOST OF THE
PCPN AHD OF THE FNT...AND THUS HAVE PCPN ENDING BY MIDDAY AS CFP
WL OCCUR BY NOON AREAWIDE. CAA MAY RESULT IN A QUICK CHGOVER TO
SHSN ON THE WRN SLOPES OF THE MTNS PRIOR TO A RAPID PCPN /AND
CLDCVR/ DECREASE. AT THE SAME TIME...WINDS WL BE INCREASING...AND
THE COMPRESSIONAL WARMING MAY YIELD MAXT WARMER THAN TDA. IT
APPEARS AS THO THE CORE OF HIER WINDS WL BE AT THE TOP /OR JUST
ABV/ THE MIXED LYR...W/ CLDS PRESENT TO INTERFERE W/ DP LYR
MIXING. THEREFORE AM KEEPING GUSTS 20-25 KT.

&&

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/...
IN A RELATIVELY SHORT AMOUNT OF TIME AFTER THE EXIT OF THE GUSTY
MONDAY SYSTEM...THE NEXT UPPER LEVEL DISTURBANCE WILL BE RIGHT ON
THE DOORSTEP TO OUR NW. THIS FEATURE WILL BE MUCH MORE COMPACT AND
THEREFORE AFFECTING MUCH LESS AREA...ALSO BEING DRIVEN BY A MORE
COMPACT ADVECTION PATTERN - TIGHTLY WOUND AROUND THE SYSTEM. AHEAD
OF AND BEHIND THIS NEXT UPPER WAVE SOME WIND...MAINLY AROUND 5-10KT
BUT GENERALLY THE SYSTEM WILL PASS W/O THE DAY-LONG PERIOD OF STRONG
WINDS BEHIND IT.

THE NEXT QUESTION IS ABOUT PRECIP AND PTYPE. THE PAST FEW RUNS OF
ALL MAIN GUIDANCE SUITES HAVE BEEN WAVERING BACK/FORTH ABOUT THE SFC
LOW TREKKING DIRECTLY OVER THE CWA...A HUNDRED MILES TO THE
NORTH...OR SOMEWHERE IN BETWEEN. THE 12Z NAM IS GOING W/ THE MASON-
DIXON LINE SOLN...BUT IN TERMS OF PRECIP - THAT MEANS VERY LITTLE
FOR AREAS S OF THE SFC LOW. MUCH OF THE PRECIP IS CARRIED ALONG
NORTH OF THE LOW...AS IT IS FOR THE EURO AND GFS BUT THEIR
DETERMINISTIC 12Z RUNS HAVE THE LOW FURTHER SOUTH - BETWEEN THE I-70
AND I-66 CORRIDOR OF THE CWA. AHEAD OF THE FEATURE...SWLY LOW LEVEL
WINDS WILL INCREASE AND SO WILL SFC TEMPS - INTO 40S/50S FROM S TO
N. ALTHOUGH A RAIN/SNOW MIX IS POSSIBLE EARLY TUE MRNG OVER THE
EXTREME NW QUAD OF THE CWA AS PRECIP ARRIVES...PRECIP EXPECTED TO BE
ALL RAIN FOR THE DAYTIME HRS AND MUCH OF IT WILL SPREAD ACROSS THE
NRN HALF OF THE CWA. KEPT A HIGH CHANCE AND SOME LIKLIES IN FOR
THESE AREAS. ON THE IMMEDIATE BACK END OF THE LOW`S PASSAGE IS STILL
SOMEWHAT IN QUESTION. THE COLD AIR W/ THE FEATURE WILL AGAIN BE
COMPACT AND CLOSE INTO THE BACK END OF THE SYSTEM. THERE MAY BE
ENOUGH OVER NERN MD FOR A BRIEF PERIOD AND THE COLD FRONT SWINGS
THRU TO MIX IN SOME SNOW BUT ALSO THE PRECIP MAY BE WELL E OF THE
AREA BY THAT TIME.

AS W/ A TYPICAL UPPER WAVE PASSAGE...THE DAY AFTER WILL BE A
MODERATED VERSION OF THE PREV DAY IN TERMS OF TEMPS AND DRY. SFC
WINDS WILL BE A STEADY NW AND DRIER BREEZE BUT NOT ALL THAT STRONG
AND HIGHS WILL BE ALLOWED TO REACH THE 50S ACROSS MUCH OF THE
AREA...NEAR 60 ACROSS THE SOUTH.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
HIGH PRESSURE...MOVING OFFSHORE THE EAST COAST...WILL SPONSOR DRY
CONDITIONS AND NEAR NORMAL TEMPERATURES WEDNESDAY NIGHT. AN
INCREASED SOUTHERLY FLOW WILL DEVELOP WEDNESDAY NIGHT AND THURSDAY
AHEAD OF AN APPROACHING COLD FRONT. HIGHS ARE EXPECTED TO APPROACH
70 DEGREES ACROSS MUCH OF THE REGION THURSDAY WITH A CHANCE OF RAIN
SHOWERS ACROSS THE WESTERN HALF OF THE REGION.

THE COLD FRONT SHOULD PUSH ACROSS THE REGION THURSDAY NIGHT
INTO FRIDAY BEFORE STALLING TO THE SOUTH FRIDAY NIGHT.
ADDITIONAL RAIN SHOWERS AND PERHAPS A THUNDERSTORM OR TWO COULD
DEVELOP IN LIEU OF THE PASSING FRONT. TEMPERATURES SHOULD REMAIN
MILD THURSDAY NIGHT AND FRIDAY WITH HIGHS REACHING THE UPPER
60S TO NEAR 70 FRIDAY.

THE STALLED FRONT SHOULD MEANDER NORTH AND SOUTH FRIDAY NIGHT
AND SATURDAY...ONLY TO REMAIN THE FOCAL ZONE FOR ADDITIONAL
RAIN SHOWERS OR RUMBLES OF THUNDER AND COOLER TEMPERATURES. A
LOW PRESSURE SYSTEM IS EXPECTED TO DEVELOP ALONG THIS FRONT BEFORE
PUSHING TO THE EAST COAST LATER SATURDAY INTO SATURDAY NIGHT.

HIGH PRESSURE WILL BRING DRIER CONDITIONS AND REINFORCING COOLER AIR
INTO THE MID ATLANTIC FOR SUNDAY.

&&

.AVIATION /02Z MONDAY THROUGH FRIDAY/...
MAINLY VFR CONDITIONS THRU MON. PSBL MVFR CIGS WITH LIGHT RAIN
TONIGHT...MAINLY BETWEEN 08-12Z. HAVE INCLUDED -RA AT THE METRO
TERMINALS FOR 3 HR BLOCKS...THE PCPN COULD VERY WELL END UP MORE
OCNL IN NATURE. LIGHT S FLOW TONIGHT...THOGUH WITH INCRSNG SW FLOW
ALOFT...HAVE INCLUDED LLWS MENTION THRU 08/09Z.

NO PCPN CONCERNS MONDAY...BUT INCRSNG WNW FLOW DURING THE
DAY...WITH GUSTS 25-30 KTS. WINDS WILL DIMINISH MONDAY NIGHT.

YET ANOTHER QUICK-MOVING UPPER LEVEL LOW WILL SWING BY THE AREA ON
TUE...MAINLY DURING THE DAYTIME HRS. ANY PCPN IS EXPECTED TO BE
RAIN...W/ WARMER TEMPS WORKING INTO THE SRN END OF THE SYSTEM AS
IT PASSES BY. BRIEF MVFR CIGS COULD RESULT FROM THIS SYSTEM DURING
THE DAYTIME HRS...BUT QUICKLY IMPROVING TUE NIGHT INTO WED AS
SKIES CLEAR OUT.

VFR CONDITIONS WEDNESDAY NIGHT. LIGHT SOUTHEAST WINDS WILL BECOME
SOUTHERLY. VFR CONDITIONS AT ALL TERMINALS THU NGT INTO FRI...EXCEPT
FOR MRB AND PERHAPS IAD WHERE MVFR COULD EVOLVE DUE TO SPOTTY RAIN
SHOWERS IN THE AREA. SOUTH WINDS BECOMING SOUTHWEST AND GUSTING
AROUND 15 KNOTS.

&&

.MARINE...
WITH WINDS AROUND 17 KTS OVER THE NORTHERN CHESAPEAKE BAY...HAVE
GONE AHEAD AND BEGUN THE SCA THERE. REMAINING WATERS HAVE THE SCA
STARTING AT MIDNIGHT...THEN ALL WATERS GO THRU THE DAY MONDAY AS
WINDS INCREASE BEHIND A PASSING COLD FRONT. EXPECTING SOLID SCA
CONDITIONS...WITH PSBL HIGHER GUSTS WITH STRONG WINDS ALOFT.
HOWEVER...BUFKIT SOUNDINGS LOOK TO RESTRICT MIXING TO THESE
STRONGEST WINDS AND THINK THE SCA WILL BE SUFFICIENT. SUB-SCA
CONDITIONS THEN EXPECTED MON NIGHT.

A COLD FRONT WILL CROSS THE REGION LATE TUE...W/ A PERIOD OF LOW-END
SCA GUSTS POSSIBLE FROM SW WINDS AHEAD OF THE FRONT. HIGH PRES WILL
CLEAR OUT THE CLOUDS/PRECIP TUE NIGHT. LOW-END SCA WINDS BEHIND THIS
FEATURE WILL PICK UP AGAIN OVER THE WATERS DURING THE DAYTIME HRS
WED.

NO MARINE HAZARDS EXPECTED WEDNESDAY NIGHT AND THURSDAY. WINDS
GENERALLY AROUND 5 KNOTS WEDNESDAY NIGHT...BECOMING SOUTH TO
SOUTHWEST AT 10 KNOTS WITH OCCASIONAL GUSTS AROUND 15 KNOTS.

&&

.TIDES/COASTAL FLOODING...
WATER LEVELS RUNNING A FOOT TO A FOOT AND A HALF BELOW ASTRO
PREDICTIONS DUE TO RECENT BLOWOUT WINDS. LEVELS SHOULD NORMALIZE
SOMEWHAT TONIGHT IN SLY FLOW. BLOWOUT TIDES WILL RETURN MON AFTN
AS NW WINDS RESUME.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 8 PM EDT MONDAY FOR ANZ530-531-538-
     539.
     SMALL CRAFT ADVISORY UNTIL 8 PM EDT MONDAY FOR ANZ532>534-537-
     540>543.
     SMALL CRAFT ADVISORY FROM 9 AM TO 8 PM EDT MONDAY FOR ANZ535-
     536.

&&

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



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