Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 020757
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
357 AM EDT THU OCT 2 2014

.SYNOPSIS...
HIGH PRESSURE WILL REMAIN OVERHEAD THROUGH TONIGHT. A STRONG COLD
FRONT WILL APPROACH THE AREA FRIDAY BEFORE PASSING THROUGH FRIDAY
NIGHT INTO EARLY SATURDAY. HIGH PRESSURE WILL RETURN FOR THE
WEEKEND...BRINGING DRIER AND NOTICEABLY COOLER CONDITIONS. THE
HIGH WILL MOVE OFFSHORE EARLY NEXT WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
A RELATIVE REPRIEVE TODAY IN BETWEEN LOW PRESSURE SYSTEMS...W/
IN-SITU HIGH PRESSURE BUILDING BRIEFLY ACROSS THE REGION - AHEAD OF
THE NEXT FRONTAL PASSAGE. THE HIGH IS CENTERED WELL OFF TO THE NORTH
AND EAST...ACROSS NEW ENGLAND...SQUEEZING DOWN THE LEE OF THE APLCNS
BEHIND A SLOWLY EXITING CUT-OFF UPPER LOW. THIS LOW WILL CONTINUE TO
SWING BACK A COUPLE OF WAVES OF LOW LEVEL MOISTURE...LOCKING-IN THE
DECENT AMOUNT OF BOUNDARY LAYER MOISTURE CAUGHT UNDERNEATH A LARGE
DRY LAYER FURTHER UP. AN AXIS OF MOISTURE CONVERGENCE IS CENTERED
ROUGHLY ACROSS THE SHEN VLY...CROSSING THE BLUE RIDGE DOWN TOWARD S
CNTRL VA. CLOUDS ARE CONTINUING TO DEVELOP AS MOISTURE BANKS INTO
EITHER SIDE OF THIS AXIS. EARLIER CLEAR SKIES OVER THE DC/BALT METRO
ARE STARTING TO FILL-IN AS THE MTNS CLOUDS ARE MEETING UP W/ COASTAL
STRATUS MOVING IN FROM THE NE.

THE TRAPPED MOISTURE LOW LEVEL MOISTURE...AS IN THE PAST FEW
DAYS...WILL GIVE THE AREA ANOTHER ROUND OF DENSE CLOUD COVER INTO
THE MID-MRNG HRS. TOWARD THE EARLY AFTN HOWEVER...MIXING OF THE
BOUNDARY LAYER FROM AN UPPER RIDGE AXIS PASSING OVERHEAD WILL
PROMOTE SOME CLEARING AND DISSIPATE MUCH OF THE EARLIER STRATUS. WE
WILL AGAIN SEE TEMPS CLIMBING INTO THE MID AND EVEN SOME UPPER 70S
BY MID-AFTN - SLIGHTLY ABOVE NORMAL. ADD DEWPOINTS IN THE L60S AND
THERE WILL BE A SLIGHT HUMID FEEL TO THE AIR...RELATIVE TO THE TIME
OF YEAR.

ANOTHER MODERATED OVERNIGHT PERIOD AGAIN TONIGHT...W/ TEMPS HOVERING
IN THE 60S FOR MUCH OF THE NIGHT AND DEWPOINTS NOT FAR BEHIND. MORE
LOW CLOUDS...STRATUS...PATCHY FOG AND SOME DRIZZLE POSSIBLE ACROSS
PARTS OF THE REGION HEADING INTO EARLY FRI.

&&

.SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/...
A VIGOROUS...POTENT...AND LARGE-SCALE LOW PRESSURE SYSTEM WILL BE
INTENSIFYING FROM LATE THU INTO FRI - OVER A GOOD HALF OF THE CONUS.
THIS WILL BE TAKING PLACE FROM THE PLAINS UP TO THE WINDWARD SIDE OF
THE APLCNS. MUCH OF THE PRECIP AND THE STRONGEST PART OF THE STORM
SYSTEM WILL BE MAKING ITS MARK ON THE UPPER MIDWEST AND GREAT LAKES
REGION LATE THU NIGHT INTO THE AFTN HRS ON FRI...JUST BEFORE
REACHING THE SPINE OF THE APLCNS. WHILE ALL THIS ACTIVITY IS
HAPPENING A TIER OF STATES TO THE WEST...WE`LL STILL BE UNDER THE
INFLUENCE OF HIGH-LEVELS OF MOISTURE CONTENT IN THE LOWEST FEW
THOUSAND FEET. MORE CLOUDS...HUMIDITY...FOG AND SOME DRIZZLE TO
START THE DAY.

HEADING INTO THE LATE MRNG HRS HOWEVER...THE BOUNDARY LAYER
CONDITIONS WILL BEGIN TO CHANGE RAPIDLY. LOW LEVEL WINDS WILL BEGIN
TO INCREASE...GRADUALLY MIXING OUT THE DENSE STRATUS DECK AND
STRENGTHENING SFC WINDS OUT OF THE S-SE. TEMPS WILL ALSO BE ON THE
INCREASE FROM THE INFLUX OF WARMER AIR FROM THE SRN ATLC. THESE
CONDITIONS WILL ADD SOME WEAK INSTABILITY TO THE AIR...SETTING UP
FOR THE EVENTUAL COLD FRONTAL PASSAGE LATER INTO THE OVERNIGHT HRS.
THE FRONT HOWEVER...IS NOT EXPECTED TO ARRIVE DURING THE WARMEST
PERIOD OF THE DAY. INSTEAD...THE OVERNIGHT PASSAGE MAY NOT BE ABLE
TO MAXIMIZE THE INSTABILITY AND WILL HAVE TO RELY ON SHEAR AND A
DRIVER FOR ANY POTENTIAL CONVECTIVE ELEMENTS AND ONGOING BATCHES OF
INCOMING PRECIP.

A STRONG COLD FRONT WILL PASS THROUGH THE AREA FRIDAY NIGHT. A
SOUTHERLY FLOW AHEAD OF THE COLD FRONT WILL USHER IN PLENTY OF
MOISTURE ACROSS OUR REGION. THE MOISTURE ALONG WITH FORCING FROM
THE FRONTAL PASSAGE WILL CAUSE SHOWERS ALONG AND AHEAD OF THE
FRONT. THE BEST CHANCE FOR SHOWERS WILL BE FRIDAY EVENING ACROSS
THE ALLEGHENY AND POTOMAC HIGHLANDS...LATE FRIDAY EVENING INTO THE
OVERNIGHT HOURS FOR THE SHENANDOAH VALLEY...AND DURING THE
OVERNIGHT HOURS FOR THE WASHINGTON AND BALTIMORE METROPOLITAN
AREAS INTO SOUTHERN MARYLAND. THE SYNOPTIC PATTERN CONTINUES TO
SUGGEST THAT A QLCS WOULD DEVELOP DUE TO THE STRONG FORCING FROM
THIS SYSTEM...BUT INSTABILITY LOOKS TO BE WEAK AND IT WILL BE
MOVING THROUGH AT AN UNFAVORABLE. THERE WILL BE STRONG WINDS ALOFT
FROM THE LOW-LEVEL JET THAT COULD MIX DOWN...BUT WITH LITTLE TO NO
INSTABILITY IT APPEARS THAT THE THREAT FOR SEVERE WEATHER IS
MINIMAL. MIN TEMPS WILL RANGE FROM THE 40S IN THE POTOMAC
HIGHLANDS WHERE COLDER AIR WILL FILTER IN BEHIND THE COLD
FRONT...TO THE LOWER AND MIDDLE 60S IN WASHINGTON/BALTIMORE INTO
LOWER SOUTHERN MARYLAND.


&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
THE COLD FRONT WILL MOVE OFF TO OUR EAST SATURDAY MORNING. A FEW
SHOWERS MAY HANG AROUND ACROSS EASTERN AREAS EARLY...BUT
NOTICEABLY COOLER AND DRIER AIR WILL FILTER INTO ALL AREAS BEHIND
THE FRONT LATER SATURDAY MORNING AND AFTERNOON.

HIGH PRESSURE WILL BUILD OVER THE REGION SATURDAY NIGHT INTO
SUNDAY...BRINGING MORE DRY AND COOL CONDITIONS. IN FACT...IT WILL
TURN OUT QUITE CHILLY ACROSS THE ALLEGHENY HIGHLANDS WHERE A FEW
LOCATIONS MAY DIP BELOW FREEZING OVERNIGHT SATURDAY ALONG THE
RIDGE TOPS.

THE HIGH WILL MOVE OFF THE COAST EARLY NEXT WEEK AND A LONGWAVE
UPPER-LEVEL TROUGH WILL DEVELOP OVER THE CENTRAL CONUS DURING THIS
TIME. A SOUTHERLY FLOW WILL CAUSE MILDER CONDITIONS. A WEAK COLD
FRONT MAY MOVE THROUGH DURING THE MIDDLE PORTION OF NEXT WEEK.
LITTLE IMPACT IS EXPECTED WITH THIS SYSTEM...BUT A COUPLE SHOWERS
CANNOT BE RULED OUT.

&&

.AVIATION /07Z THURSDAY THROUGH MONDAY/...
THE APLCNS TO THE BLUE RIDGE CONTINUE TO BE THE FOCAL ZONE OF
TRAPPED LOW LEVEL MOISTURE...WHICH IS HELPING TO CREATE A WIDE ARRAY
OF LOW CLOUDS AND FOG. MOST OBS ACROSS THE MID-ATLC ARE SHOWING A
HIGHER-END FOG IN THE 2-5SM RANGE...W/ ONLY ISOLATED LOWER VALUES.
MORE SITES WILL CONTINUE TO DROP AS SFC CONDITIONS SATURATE BUT IT
WILL BE A CHALLENGE TO GET WIDESPREAD DENSE FOG W/ THE VARYING LOW
LEVEL WIND PROFILES AND SCT CLOUD DECK HEIGHTS.

HIGH PRESSURE WILL EVENTUALLY HELP CLEAR OUT MUCH OF THE DENSE MRNG
STRATUS TOWARD THE MID-LATE MRNG HRS...THEN WEAK ONSHORE FLOW WILL
AGAIN TAKE OVER THE SFC FLOW. MORE PATCHY FOG AND LOW CLOUDS
POSSIBLE AGAIN OVERNIGHT TONIGHT.

A COLD FRONT WILL PASS THROUGH THE TERMINALS LATE FRIDAY NIGHT.
SHOWERS AND SOUTHERLY WINDS ARE EXPECTED AHEAD OF THE FRONT.
MVFR/IFR CIGS ARE ALSO EXPECTED AS MOISTURE CONTINUES TO MOVE IN
FROM THE SOUTH. THE WINDS WILL SHIFT TO THE WEST-NORTHWEST
EARLY SATURDAY MORNING BEHIND THE FRONT. MUCH DRIER AIR WILL MOVE
IN DURING THIS TIME ALLOWING FOR VFR CONDITIONS. VFR CONDITIONS
AND GUSTY WEST-NORTHWEST WINDS ARE EXPECTED FOR THE REST OF
SATURDAY.

HIGH PRESSURE WILL SLOWLY MOVE OFF TO THE EAST SUNDAY AND
MONDAY...ALLOWING FOR A SOUTHERLY FLOW TO RETURN. VFR CONDITIONS
ARE LIKELY DURING THIS TIME.

&&

.MARINE...
AN UPPER LOW SLOWLY MOVING OFF THE NEW ENGLAND COAST AND HIGH
PRESSURE CENTERED JUST NORTH OF THERE ARE PUMPING IN ELY ONSHORE
FLOW OVERNIGHT AND WILL CONTINUE TO THROUGHOUT THE DAY. DRY WX TODAY
AND ONLY A LIGHT E-SE ONSHORE FLOW TONIGHT INTO THU...AS A HIGH PRES
RIDGE MOVES ACROSS THE AREA INTO EARLY FRI. A STRONG COLD FRONT WILL
BE ON THE WAY ON FRIDAY...THOUGH STILL FAIRLY FAR OFF TO THE WEST
DURING THE DAYTIME HRS. EVEN STILL...SCA CONDITIONS WILL BECOME MORE
PROBABLE LATER IN THE AFTN AS THE FRONT NEARS THE AREA.

A COLD FRONT WILL PASS THROUGH THE WATERS LATE FRIDAY NIGHT INTO
SATURDAY MORNING. GUSTY SOUTHERLY WINDS ARE EXPECTED AHEAD OF THE
FRONT. WINDS WILL SHIFT TO THE WEST-NORTHWEST BEHIND THE FRONT.
HIGH PRESSURE WILL BUILD OVERHEAD SATURDAY NIGHT BEFORE SLOWLY
MOVING OFF THE COAST SUNDAY AND MONDAY. WINDS WILL SHIFT TO THE
SOUTH FOR SUNDAY AND MONDAY. A SMALL CRAFT ADVISORY WILL LIKELY BE
NEEDED FOR PORTIONS OF THE WATERS FRIDAY NIGHT THROUGH MONDAY.


&&

.TIDES/COASTAL FLOODING...
TIDAL ANOMALIES ARE AROUND ONE FOOT ABOVE NORMAL EARLY THIS
MORNING. THIS HAS CAUSED MINOR TIDAL FLOODING NEAR HIGH TIDE. THE
TIDAL ANOMALIES SHOULD REMAIN NEARLY STEADY THROUGH TODAY. THE
NEXT HIGH TIDE CYCLE THIS AFTERNOON WILL BE THE LOWER OF THE
TWO...SO WATER LEVELS SHOULD NOT BE QUITE AS HIGH AS THEY WERE
LATE WEDNESDAY NIGHT AND EARLY THIS MORNING. HOWEVER...MINOR TIDAL
FLOODING FOR SENSITIVE AREAS IS STILL POSSIBLE NEAR HIGH TIDE THIS
AFTERNOON FOR THE WESTERN SHORE OF THE MARYLAND CHESAPEAKE BAY
ESPECIALLY FROM ANNE ARUNDEL COUNTY THROUGH ST MARYS COUNTY.

THE POSITIVE TIDAL ANOMALIES WILL CONTINUE TONIGHT AND THE HIGH
TIDE WILL BE THE HIGHER OF THE TWO ASTRONOMICAL NORMS.
THEREFORE...MINOR FLOODING IS EXPECTED WITH THIS HIGH TIDE CYCLE.
CONFIDENCE IS HIGHEST FROM ANNE ARUNDEL THROUGH ST MARYS
COUNTIES SO A COASTAL FLOOD ADVISORY IS IN EFFECT FOR THESE
AREAS. HOWEVER...A COASTAL FLOOD ADVISORY MAY STILL BE NEEDED FOR
AREAS ALONG THE UPPER TIDAL POTOMAC RIVER AND THE REST OF THE
WESTERN SHORE ALONG THE CHESAPEAKE BAY.

A SOUTHERLY FLOW WILL INCREASE AHEAD OF A COLD FRONT FRIDAY INTO
FRIDAY NIGHT. MINOR TIDAL FLOODING IS LIKELY NEAR HIGH TIDE...WITH
THE HIGHEST WATER LEVELS EXPECTED DURING THE HIGH TIDE CYCLE
FRIDAY NIGHT INTO EARLY SATURDAY. THE FLOW WILL TURN OFFSHORE
BEHIND THE COLD FRONT LATER SATURDAY AND ANOMALIES SHOULD SHARPLY
DECREASE.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...COASTAL FLOOD ADVISORY UNTIL 4 AM EDT FRIDAY FOR MDZ014-017-
     018.
VA...NONE.
WV...NONE.
MARINE...NONE.

&&

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







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