Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 241348
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
948 AM EDT THU APR 24 2014

.SYNOPSIS...
HIGH PRESSURE WILL BUILD OVER THE AREA THROUGH TODAY BEFORE
GRADUALLY SHIFTING TO THE EAST TONIGHT. A COLD FRONT WILL PASS
THROUGH THE AREA FRIDAY AND ANOTHER COLD FRONT IS EXPECTED TO MOVE
THROUGH LATE SATURDAY THROUGH SATURDAY NIGHT. HIGH PRESSURE WILL
BUILD IN ON SUNDAY AS THE COLD FRONT STALLS TO OUR SOUTH. SEVERAL
WAVES OF LOW PRESSURE WILL DEVELOP ALONG THE STALLED
BOUNDARY...BRINGING UNSETTLED CONDITIONS TO THE AREA NEXT WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
NORTHWEST WINDS WILL CONTINUE ACROSS MOST OF THE REGION THIS MORNING
AS HIGH PRESSURE MOVES INTO THE WEST AND LOW PRESSURE DEPARTS ACROSS
THE NRN ATLANTIC. THE TIGHT PRESSURE GRADIENT EAST OF THE POTOMAC
RIVER AND BLUE RIDGE WILL LEAD TO BREEZY CONDITIONS FOR THE ABOVE MENTIONED
AREA. THE GRADIENT WILL SHIFT TO THE EAST THIS AFTERNOON AND WINDS
WILL DECREASE BY THIS AFTERNOON. TEMPS WILL RISE INTO THE 60S
TODAY WHICH IS SLIGHTLY BELOW CLIMO.

MOISTURE WILL MOVE AROUND AN UPPER LEVEL RIDGE ACROSS THE OHIO
VALLEY AND MID TO HIGH LEVEL CLOUDS WILL MOVE ACROSS THE CENTRAL
FOOTHILLS AND POTOMAC HIGHLANDS THIS MORNING.

PREVIOUS DISCUSSION...
THE HIGH WILL GRADUALLY SHIFT TOWARD MID-ATLANTIC COAST TONIGHT
ALONG WITH THE UPPER-LEVEL RIDGING. A POTENT SHORTWAVE AND ITS
ASSOCIATED SURFACE LOW WILL TRACK INTO THE MIDWEST DURING THIS
TIME. THERE WILL BE SOME HIGH AND MID- LEVEL CLOUDS INCREASING
OVERNIGHT...BUT DRY CONDITIONS WILL PERSIST. MIN TEMPS WILL RANGE
FROM THE UPPER 30S ACROSS PORTIONS OF NORTHERN MARYLAND WHERE
THERE MAY BE SOME RADIATIONAL COOLING TO NEAR 50 IN DOWNTOWN
WASHINGTON AND BALTIMORE.

&&

.SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/...
THE SHORTWAVE AND SURFACE LOW WILL TRACK INTO THE OHIO VALLEY
FRIDAY MORNING BEFORE MOVING INTO OUR AREA FRIDAY AFTERNOON. THE
COLD FRONT ASSOCIATED WITH THE SURFACE LOW WILL ALSO MOVE INTO OUR
AREA DURING THIS TIME. A SOUTHERLY FLOW WILL INCREASE AHEAD OF THE
BOUNDARY...ALLOWING FOR WARM AND MOIST AIR TO MOVE INTO THE
REGION. GUIDANCE HAS TRENDED A BIT SLOWER WITH THIS SYSTEM...WHICH
WILL ALLOW FOR SOME MORE MOISTURE TO MAKE IT INTO THE AREA BEFORE
IT MOVES THROUGH. THEREFORE...POPS HAVE BEEN INCREASED AND
WIDESPREAD SHOWERS ARE EXPECTED. THE BEST CHANCE FOR PRECIPITATION
WILL BE FROM MID-MORNING THROUGH THROUGH FRIDAY AFTERNOON WEST OF
THE BLUE RIDGE MOUNTAINS...AND FRIDAY AFTERNOON EAST OF THE BLUE
RIDGE MOUNTAINS.

THERE WILL BE ENOUGH WARM AND MOIST AIR FOR SOME INSTABILITY TO
DEVELOP AS WELL. THEREFORE...A FEW THUNDERSTORMS CANNOT BE RULED
OUT. CLOUD COVER AND MARINE AIR SHOULD KEEP INSTABILITY LIMITED
ENOUGH TO KEEP THE SEVERE THREAT MAINLY TO OUR SOUTH.
HOWEVER...SHOULD THERE BE MORE SUNSHINE THAT BREAKS OUT...THEN
SEVERE THUNDERSTORMS WOULD BE POSSIBLE DUE TO FAVORABLE SHEAR
PROFILES...ESPECIALLY ACROSS CENTRAL VIRGINIA.

MOST MODELS STILL A BIT DIVERGENT IN THE PROGRESS/SPEED OF THE UPPER
LEVEL FEATURE THAT IS EXPECTED TO SLIDE ACROSS OUR REGION ON FRI...
EXITING LATE FRI NIGHT. A BULK OF THE PRECIP WILL HAVE ALREADY MOVED
THRU EARLIER IN THE DAY...W/ THE BACK END SUBSIDENCE MOVING ANY
LINGERING PRECIP OFF THE COAST LATE FRI NIGHT. THE DRIER AIR INFLUX
WILL HELP DROP DEWPOINTS A FEW DEGREES FROM THEIR EARLIER
VALUES...BUT STILL PLENTY MOIST WHICH WILL KEEP OVERNIGHT LOWS IN
THE U40S-L50S.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
OVER THE PAST SEVERAL YEARS...HAVE SEEN A NUMBER OF LATE APRIL
CLOSED UPPER LOWS THAT MEANDER AND DRIFT OVER A PORTION OF EITHER
THE UPPER MIDWEST/OHIO VLY OR DEEP SOUTH AND EVENTUALLY OFF THE ATLC
COAST. CANNOT REMEMBER SEEING/FORECASTING ONE AS LARGE AS THE ONE
LONG RANGE GUIDANCE IS DEPICTING FOR THE BETTER PART OF NEXT WEEK.
ONE OF THE REASONS THIS SYSTEM WILL LIKELY BE SO VAST IS THAT IT
ORIGINALLY WILL HAVE STARTED OUT AS TWO SEPARATE UPPER WAVES THAT
COMBINE OVER THE UPPER MIDWEST.

THE FRIDAY UPPER WAVE AFFECTING OUR AREA WILL SLIDE OFF THE MID ATLC
COASTLINE AND STALL BASICALLY OFF THE SRN NEW ENGLAND COAST THIS
WEEKEND. MEANWHILE...A COLD AND DEEP UPPER WAVE OVER THE INTER-MTN
WEST WILL BE GEARING UP FOR AN INTENSIFICATION ONCE IT MOVES EAST OF
THE ROCKIES THIS COMING WEEKEND. THE STALLED NEW ENGLAND COASTAL LOW
WILL PREVENT THE FORWARD PROGRESS OF THE NOW LARGE-SCALE UPPER
SYSTEM OVER THE NRN PLAINS SUN/MON...AND ALSO SQUEEZE DOWN A COLDER
UPPER VORT DOWN FROM HUDSON VLY IN BETWEEN THE TWO LARGER SYSTEMS.
THE CONTINUAL ROTATION OF SMALLER VORT LOBES AROUND THE PARENT
SYSTEM WILL KEEP AN ACTIVE PERIOD OF WX FOR ROUGHLY THE ENTIRE ERN
HALF OF THE CONUS FOR MOST OF NEXT WEEK.

CLOSED UPPER LOWS TYPICALLY PRESENT A NUMBER OF FORECAST
CHALLENGES...AND THE DAILY DEPICTIONS OF THIS FEATURE WILL BE AN
INTRIGUING STORY FOR THE NEXT SEVERAL DAYS. EACH PHASING PERIOD OF
THIS SYSTEM COULD CAUSE ANOTHER ROUND OR WAVE OF PRECIP ACROSS OUR
REGION W/ PERIODIC BREAKS IN BETWEEN. COMPARING THE GFS AND EURO`S
LATEST VERSIONS - THE GFS IS A MUCH COLDER AND COMPACT UPPER LOW
SLIDING OVER THE UPPER MIDWEST WHILE THE EURO...THOUGH SHOWING SOME
SIMILAR PROGRESS AND INTERACTIONS - NOT AS STRONG AS THE GFS. THE
CURRENT FORECAST FOR OUR AREA REVOLVES ESSENTIALLY AROUND A WET
MIDDLE OF THE WEEK PERIOD...W/ A SLOW BUILD UP TO IT THIS WEEKEND
INTO EARLY NEXT WEEK. TEMPS UNDER THIS TYPE OF REGIME WOULD BE WELL
BELOW AVG BUT NOT VERY COLD - MORE LIKE A MODERATED ENVIRONMENT W/
LITTLE DIURNAL CHANGE.

&&

.AVIATION /14Z THURSDAY THROUGH MONDAY/...
VFR CONDITIONS ARE EXPECTED THROUGH TONIGHT. NORTHWEST WINDS WILL
GUST AROUND 15 TO 20 KNOTS THIS MORNING THROUGH MID-AFTERNOON
ACROSS THE EASTERN TERMINALS. HIGH PRESSURE WILL ALLOW FOR LIGHT
WINDS TONIGHT.

SOUTHERLY WINDS WILL INCREASE AHEAD OF A COLD FRONT FRIDAY WITH
GUSTS AROUND 15 TO 20 KNOTS EXPECTED IN THE AFTERNOON. SHOWERS ARE
EXPECTED...ESPECIALLY DURING THE AFTERNOON. CIGS/VSBYS WILL LOWER
TO MVFR LEVELS AND POSSIBLY IFR LEVELS IN BANDS OF HEAVIER
SHOWERS.

A QUIET WX WEEKEND IN STORE...AS ONE UPPER LEVEL SYSTEM MOVES OFF
THE COAST FRI NIGHT - ALLOWING HIGH PRESSURE TO SQUEEZE IN OVER THE
AREA SAT/SUN AND LASTING THRU LATE MON. HOWEVER...THE FRI/FRI NIGHT
SYSTEM WILL HANG OUT OFF THE NEW ENGLAND COAST AND HELP STEER A COLD
UPPER LOW INTO A LARGE AND POTENT LOW PRESSURE SYSTEM OVER THE NRN
PLAINS. THESE FEATURES WILL EVENTUALLY COMBINE INTO A LARGER SYSTEM
THAT WILL SLOWLY DRIFT TOWARD AND OVER THE AREA FOR MUCH OF NEXT
WEEK...STARTING LIKELY TUE AND ONWARD. PERIODS OF RAIN AND
PERIODICALLY LOWERED FLIGHT CATEGORIES WILL LIKELY BE COMMON INTO
THE MIDDLE AND LATTER PARTS OF NEXT WEEK.

&&

.MARINE...
A SMALL CRAFT ADVISORY IS IN EFFECT FOR THE WATERS TODAY. MIXING
WILL CONTINUE THIS MORNING AND SHOULD CAUSE GUSTS AROUND 20 KNOTS
LATER THIS MORNING INTO EARLY THIS AFTERNOON. THE PRESSURE
GRADIENT WILL DECREASE THIS AFTERNOON AND WINDS WILL DIMINISH
DURING THIS TIME FROM WEST TO EAST. THE SMALL CRAFT ADVISORY MAY
BE ABLE TO BE CANCELLED LATER THIS AFTERNOON,

HIGH PRESSURE WILL ALLOW FOR LIGHTER WINDS TONIGHT. NO MARINE
HEADLINES ARE EXPECTED. A SOUTHERLY FLOW WILL INCREASE AHEAD OF A
COLD FRONT FRIDAY. A SMALL CRAFT ADVISORY IS IN EFFECT FOR THE
WATERS FRIDAY AFTERNOON. SHOWERS WILL DEVELOP DURING THE
AFTERNOON.

A SFC LOW IS EXPECTED TO PASS BY THE NRN PART OF THE BAY FRI
NIGHT...BUT THEN WINDS WILL PICK UP AGAIN BEHIND THE LOW. WINDS WILL
THEN CONTINUE TO GUST INTO SAT...W/ PERIODS OF BREEZY CHANNELING
WINDS OVER THE BAY/TP INTO NEXT WEEK. A BREEZY SAT WILL GIVE WAY TO
A QUIET START TO NEXT WEEK...AS HIGH PRESSURE MOVES IN - THEN OUT BY
LATE MON/EARLY TUE. ONSHORE FLOW WILL THEN BEGIN AHEAD OF ANOTHER
SYSTEM FOR MID NEXT WEEK.

&&

.FIRE WEATHER...
A NORTHWEST FLOW HAS CAUSED DEWPOINTS TO DROP SEVERAL DEGREES
COMPARED TO WEDNESDAY. THEREFORE...THE RELATIVE HUMIDITY WILL BE
SIGNIFICANTLY LOWER TODAY WITH MIN RH VALUES AROUND 15 TO 25
PERCENT THIS AFTERNOON. GUSTY NORTHWEST WINDS ARE STILL EXPECTED
ACROSS NORTHEASTERN MARYLAND SO A RED FLAG WARNING IS IN EFFECT.
ELSEWHERE...WINDS MAY GUST AROUND 15 TO 20 MPH THIS MORNING INTO
EARLY THIS AFTERNOON...ESPECIALLY EAST OF THE BLUE RIDGE
MOUNTAINS. HOWEVER...WINDS SHOULD DIMINISH THIS AFTERNOON AS HIGH
PRESSURE BUILDS OVERHEAD. THEREFORE...NO FIRE WEATHER HEADLINES
ARE IN EFFECT.

WINDS WILL BE LIGHT TONIGHT WITH A STRONG NOCTURNAL INVERSION.
SOUTHERLY WINDS WILL INCREASE FRIDAY AND SHOWERS WILL DEVELOP
AHEAD OF A COLD FRONT. THE BEST CHANCE FOR SHOWERS WILL BE FRIDAY
MORNING AND FRIDAY AFTERNOON WEST OF THE BLUE RIDGE MOUNTAINS...AND
FRIDAY AFTERNOON INTO FRIDAY NIGHT EAST OF THE BLUE RIDGE
MOUNTAINS. RAINFALL AMOUNTS WILL AVERAGE BETWEEN ONE-QUARTER AND
ONE-HALF INCH ACROSS MOST LOCATIONS. HOWEVER...LOCALLY HIGHER
AMOUNTS ARE LIKELY SINCE THERE WILL BE A CONVECTIVE ELEMENT TO THE
PRECIPITATION.

&&

.TIDES/COASTAL FLOODING...
A SOUTHERLY FLOW WILL STRENGTHEN AHEAD OF A COLD FRONT FRIDAY
AFTERNOON THROUGH FRIDAY EVENING. THIS WILL CAUSE TIDAL ANOMALIES
TO SHARPLY INCREASE. THE FLOW WILL TURN OFFSHORE BEHIND A COLD
FRONT AFTER MIDNIGHT...CAUSING TIDAL ANOMALIES TO DECREASE BY
SATURDAY MORNING. MINOR COASTAL FLOODING IS POSSIBLE NEAR TIMES
OF HIGH TIDE FRIDAY NIGHT...ESPECIALLY IF THE ARRIVAL OF THE
OFFSHORE FLOW IS DELAYED A BIT.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...RED FLAG WARNING UNTIL 6 PM EDT THIS EVENING FOR MDZ005>007-
     010-011-014.
VA...NONE.
WV...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 6 PM EDT THIS EVENING FOR
     ANZ530>543.
     SMALL CRAFT ADVISORY FROM NOON TO 6 PM EDT FRIDAY FOR
     ANZ530>543.

&&

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







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