Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 281420
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1020 AM EDT THU APR 28 2016

.SYNOPSIS...
A COLD FRONT WILL REMAIN STALLED TO THE SOUTH THROUGH FRIDAY.
WAVES OF LOW PRESSURE WILL RIDE ALONG THE BOUNDARY DURING THIS
TIME. THE BOUNDARY WILL DROP FARTHER SOUTH SATURDAY...BUT IT WILL
THEN LIFT NORTHWARD CLOSER TO THE REGION AGAIN SUNDAY AND MONDAY
AS ANOTHER WAVE OF LOW PRESSURE MOVES ALONG IT.

&&

.NEAR TERM /THROUGH TONIGHT/...
LTL SYNOP CHG TO FCST THIS MRNG. STALLED SFC BOUNDARY STILL
LOCATED NEAR NC...SNAKING TO VERTICALLY STACKED LOW PRESSURE OVER
IOWA. MARITIME FLOW DOMINATES WITH PLENTY OF CLOUD COVER. A SWATH
OF SHRA STRETCHES FM THE PTMC HIGHLANDS ACRS METRO DC TO SRN MD.
BEHIND THIS ACTIVITY...FAIRLY SUBSTANTIAL DRY SLOT IS NOTED IN
WATER VAPOR IMAGERY. THIS WILL LIKELY LEAD TO RAPIDLY DIMINISHING
COVERAGE OF SHOWERS DURING THE AFTERNOON. HOWEVER...WITH
ADDITIONAL WEAK SHORTWAVE ENERGY AND CONTINUED OVERRUNING...SOME
LIGHT SHOWERS OR SPRINKLES WILL REMAIN POSSIBLE. IN ADDITION...BL
HEATING WILL TAKE PLACE S/W OF THE CWA IN AN ENVIRONMENT OF
MODERATE DEEP LAYER SHEAR. SOME OF THIS THUNDERSTORM ACTIVITY MAY
PUSH INTO THE POTOMAC HIGHLANDS AND ALONG THE SOUTHERN CWA BORDER
THIS AFTERNOON.

HV MADE TIMING ADJUSTMENTS IN DATABASE TO ACCNT FOR THIS THINKING
AND LTST RADAR TRENDS. ON THE WHOLE...PREV THOUGHT PROCESS REMAINS
VALID. CONSIDERING CURRENT RAFL AND LTST LAMP...HV ADJUSTED TEMPS
DOWN ARND MUCH OF MD AND ADJACENT VA. AM NOT TOUCHING CENTRAL
FOOTHILLS/CENTRAL SHEN VLY AS TEMPS CUD JUMP THERE QUITE QUICKLY.

THE OPENED LOW WILL BE NEAR PA TONIGHT. THUS THE HIGHEST POPS
WILL BE IN THE NORTHERN CWA. LOW LEVELS WILL BE SATURATED ACROSS
THE ENTIRE AREA THOUGH...SO HAVE INTRODUCED PATCHY DRIZZLE AND FOG
TO THE FORECAST. LOWS WILL RANGE FROM THE MID 40S TO MID 50S.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
WEAK SFC LOW WILL STILL BE NEAR THE AREA ON FRIDAY WITH CAD WEDGE
FRONT NEARLY UNCHANGED. HOWEVER...TREND IN 00Z GUIDANCE IS TO KEEP
SHORTWAVE TROUGH FARTHER TO THE NORTH. SO SEE LITTLE REASON TO
CHANGE POPS...CAPPING IN THE CHANCE CATEGORY WITH HIGHEST NEAR PA
BORDER. THE LOW MAY DRAW SOME WARMER AIR INTO CENTRAL VA...BUT
HIGHS WILL REMAIN IN THE MID 50S NEAR THE PA BORDER. ANY CHANCE OF
MEASURABLE PRECIP WILL END FRIDAY EVENING AS THE DEPARTING LOW
DRAGS THE FRONT SOUTH AND HIGH PRESSURE BUILDS. THERE WILL STILL
BE LOW LEVEL OVERRUNNING...SO COULD SEE SOME LINGERING DRIZZLE.

THE FIRST HALF OF SATURDAY SHOULD BE DRY AS SHORTWAVE RIDGING
MOVES OVERHEAD. HOWEVER...THE TREND HAS BEEN FASTER WITH
ISENTROPIC LIFT AHEAD OF THE NEXT LOW OVER THE PLAINS...WITH RAIN
POSSIBLE ACROSS WESTERN AREAS BY AFTERNOON AND ACROSS MOST OF THE
AREA OVERNIGHT. HIGHS MAY GET A BOOST FROM MIDDAY SUN
BREAKS...POTENTIALLY REACHING THE 60S IN MOST AREAS.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
GUIDANCE THROUGH MONDAY IS IN REASONABLE...IF ROUGH...AGREEMENT.
THE STATIONARY BOUNDARY TO OUR SOUTH WILL START TO LIFT NORTH AS
ANOTHER WAVE OF LOW PRESSURE TRACKS EASTWARD FROM THE CENTRAL
PLAINS AND OHIO VALLEY. THE WEDGE OF COOLER AIR WILL BE HARD TO
DISLODGE AND WHILE SOME MILDER AIR MAY TRY TO ENTER THE CWA LATE
SUNDAY OR MONDAY...MOST OF THE REGION WILL PROBABLY STAY ON THE
COOL SIDE OF THE BOUNDARY. AFTER THE TROUGH AXIS ALOFT PASSES
THROUGH LATE MONDAY...GUIDANCE DIFFERS IN THE POTENTIAL FOR
ANOTHER WAVE TO MOVE NORTHEASTWARD UP THE COAST...SO WE MAINTAIN A
CHANCE OF SHOWERS. OTHER THAN THE BRIEF CHANCE OF A WARM
INTERLUDE WITH THE PASSING WAVE LATE SUNDAY INTO
MONDAY...TEMPERATURES WILL BE ON THE COOL SIDE OF NORMAL.

&&

.AVIATION /14Z THURSDAY THROUGH MONDAY/...
OVERALL THEME OF FORECAST DOES NOT CHANGE APPRECIABLY THROUGH
FRIDAY NIGHT AS THE REGION WILL REMAIN ENTRENCHED IN MARITIME
FLOW/CAD WEDGE. MAIN ISSUE WILL BE TIMING IN IFR RESTRICTION (MORE
LIKELY OVERNIGHT THAN DURING DAY). FOG...SHOWERS...AND DRIZZLE
COULD REDUCE VSBY AT TIMES...BUT CLOUDS WILL BE THE BIGGER ISSUE.
BEST CHANCE AT POTENTIALLY MODERATE RAIN WILL CROSS THE AREA
DURING THE MID MORNING HOURS (QUICKER THAN PREVIOUS FORECASTS).
ANY AFTERNOON THUNDERSTORMS SHOULD STAY SOUTH OF CHO. COULD SEE A
RISE TO SOLID VFR CONDITIONS ON SATURDAY...BUT ADDITIONAL RAIN AND
LOW CLOUDS WILL ARRIVE SATURDAY NIGHT AND CONTINUE THROUGH MONDAY
IF NOT LONGER.

&&

.MARINE...
ONSHORE FLOW WILL CONTINUE THROUGH SATURDAY. GENERALLY EXPECTING
5- 10 KT WITH OCCASIONAL INCREASES TO 15 KT. SOME GUIDANCE
INDICATES PERIODIC FLIRTING WITH SCA-LEVEL GUSTS THIS
AFTERNOON...BUT LACK OF CONSISTENT SIGNAL PRECLUDES A HEADLINE FOR
NOW. SAME GOES FOR FRIDAY AFTERNOON. WINDS MAY TURN MORE TO THE SE
SATURDAY NIGHT BUT REMAIN SUB-SCA. BETTER CHANCE OF SCA CONDITIONS
SUNDAY AND MONDAY WITH A MORE POTENT LOW PRESSURE SYSTEM MOVING
THROUGH.

&&

.TIDES/COASTAL FLOODING...
WATER LEVELS REMAIN ANOMALOUSLY HIGH DUE TO EASTERLY FLOW ALONG
THE WESTERN SHORE OF THE CHESAPEAKE BAY AND PORTIONS OF THE TIDAL
POTOMAC. WITH MINOR FLOODING OCCURRING ALONG THE CHESAPEAKE...WILL
KEEP COASTAL FLOOD ADVISORIES IN PLACE INTO THE EARLY
AFTERNOON...EXCEPT ST MARYS COUNTY WHERE HIGH TIDE HAS PASSED AND
WATER LEVELS ARE DROPPING. HAVE ALSO ISSUED ADVISORIES ALONG THE
TIDAL POTOMAC IN THE DC METRO AREA WITH MINOR FLOODING FORECAST
THIS AFTERNOON. WITH OUR AREA EXPECTED TO REMAIN ON THE NORTH SIDE
OF THE FRONT WITH PERSISTENT EASTERLY FLOW...MINOR FLOODING WILL
REMAIN A CONCERN FOR THE NEXT SEVERAL DAYS.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...COASTAL FLOOD ADVISORY UNTIL 4 PM EDT THIS AFTERNOON FOR
     DCZ001.
MD...COASTAL FLOOD ADVISORY UNTIL NOON EDT TODAY FOR MDZ018.
     COASTAL FLOOD ADVISORY UNTIL 3 PM EDT THIS AFTERNOON FOR
     MDZ011-014.
VA...COASTAL FLOOD ADVISORY UNTIL 4 PM EDT THIS AFTERNOON FOR
     VAZ054.
WV...NONE.
MARINE...NONE.

&&

$$
SYNOPSIS...RCM
NEAR TERM...ADS/HTS
SHORT TERM...ADS
LONG TERM...RCM
AVIATION...ADS/RCM
MARINE...ADS/RCM
TIDES/COASTAL FLOODING...MJM/RCM



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