Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 220045 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 845 PM EDT SUN SEP 21 2014 .SYNOPSIS...
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A COLD FRONT IS MOVING THROUGH THE REGION THIS EVENING. HIGH PRESSURE WILL BUILD OVER THE AREA MONDAY INTO TUESDAY...THEN SHIFT OVER NEW ENGLAND THROUGH LATE WEEK.
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&& .NEAR TERM /THROUGH MONDAY/...
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SFC ANLYS SHOWS CD FNT HAS PUSHED E OF THE BLU RDG AND WL MAKE IT THRU THE WATERS B4 MDNGT. ISOLD SHRA ONGOING BUT THE SVR THREAT IS GONE. HIGH PRES WL BUILD INTO THE AREA AFTR MDNGT. NWLY FLOW SPREADS IN BEHIND THE FRONT WITH GUSTS GENERALLY 25 TO 30 MPH. MIN TEMPS ELEVATED IN MIXING FLOW IN SPITE OF COOLER AIR COMING IN. MID TO UPR 50S INLAND...LOW TO MID 60S NEARSHORE. UPSLOPE RAIN SHOWERS CONTINUE THROUGH THE NIGHT WEST FROM THE ALLEGHENY FRONT. A FEW UPSLOPE SPRINKLES WEST FROM THE ALLEGHENY FRONT MONDAY MORNING. OTHERWISE DRY WITH NWLY GUSTS 25 MPH DECREASING THROUGH THE AFTERNOON. GOOD MIXING AND 850MB TEMPS OF 4-6C SUGGEST MAX TEMPS IN THE LOW TO MID 70S.
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&& .SHORT TERM /MONDAY NIGHT THROUGH TUESDAY NIGHT/...
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HIGH PRESSURE CONTINUES TO BUILD MONDAY NIGHT WITH THE GRADIENT SLACKING PARTICULARLY WEST OF THE BLUE RIDGE BY DAYBREAK TUESDAY. WITH DRY AIR IN PLACE...MIN TEMPS COULD BE IN THE MID 30S IN WRN VALLEYS AND THE POTOMAC HIGHLANDS. SINCE THIS IS THE SHELTER TEMPERATURE (ABOUT SIX FEET OFF THE GROUND) GROUND TEMPERATURES COULD HIT FREEZING AND THUS CAUSE FROST. A MENTION FOR FROST WILL BE PUT IN THE HWO FOR OUT THERE. OTHERWISE...SUB NORMAL MIN TEMPS WITH LOW TO MID 40S PIEDMONT AND WEST...UPR 40S INLAND COASTAL LOW LANDS AND LOW TO MID 50S URBAN/NEARSHORE. HIGH PRESSURE SHIFTS TO THE NORTHERN MID-ATLANTIC TUESDAY AND TUESDAY NIGHT. CONTINUED DRY CONDITIONS WITH NLY FLOW AND BELOW NORMAL TEMPS.
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&& .LONG TERM /WEDNESDAY THROUGH SUNDAY/... HIGH PRESSURE OVER NEW ENGLAND WILL SLOWLY MOVE OUT INTO THE NORTHWESTERN ATLANTIC AS A BROAD AREA OF LOW PRESSURE DRIFTS WESTWARD INTO THE SOUTHEASTERN CONUS. A MOIST EASTERLY FLOW IN A TIGHTENING GRADIENT BETWEEN THESE TWO FEATURES WILL RESULT IN INCREASING CLOUDS THROUGHOUT THE DAY WEDNESDAY...WITH ABUNDANT CLOUD COVER IN A MARITIME AIRMASS EXPECTED TO PERSIST INTO THE END OF THE WEEK. THE OPERATIONAL 00Z ECMWF MODEL WAS DEFINITELY THE MOST AGGRESSIVE WITH THE NORTHWARD EXTENT OF PRECIP ASSOCIATED WITH LOW PRESSURE TO THE SOUTH IN THE THURSDAY-FRIDAY TIMEFRAME...BUT DOES NOT HAVE OVERWHELMING SUPPORT FROM ITS OWN ENSEMBLE MEMBERS. THERE IS A HIGH CHANCE FOR PERIODS OF DRIZZLE DURING THIS PERIOD GIVEN THE PERSISTENT EASTERLY FLOW...BUT MEASURABLE PRECIPITATION ASSOCIATED WITH THE LOW WELL TO THE SOUTH APPEARS RELATIVELY LOW AT THE MOMENT. HAVE KEPT POPS VERY LOW FOR THIS REASON. AS THE LOW PRESSURE OVER THE SOUTHEAST WEAKENS AND THE HIGH PRESSURE MOVES FURTHER OFFSHORE...UPPER-LEVEL RIDGING WILL RE-STRENGTHEN AND RESULT IN SOUTHERLY FLOW AT THE SURFACE WITH A WARMING TREND EXPECTED BY NEXT WEEKEND. && .AVIATION /01Z MONDAY THROUGH FRIDAY/...
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NWLY FLOW GUSTS 20 TO 25 KT BEHIND THE COLD FRONT TONIGHT THROUGH MONDAY. VFR AND NLY FLOW THEN TUESDAY WITH HIGH PRESSURE SPREADING NORTH OF THE AREA. SUB-VFR CONDITIONS APPEAR INCREASINGLY LIKELY WITH LOW CLOUDS/FOG MAKING A VISIT TO THE AREA WED-THU NIGHT. WINDS GENERALLY EASTERLY 10-15 KNOTS WITH A FEW GUSTS TO 20 KNOTS POSSIBLE.
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&& .MARINE...
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SCA THROUGH MONDAY WITH GUSTS IN THE MORNING AROUND 25 KT... SLOWLY EASING THROUGH THE AFTERNOON. NLY THEN NELY FLOW AS HIGH PRESSURE SHIFTS NORTH TUESDAY. WINDS INCREASE TO NEAR SCA LEVELS DURING THE MIDDLE PART OF THE WEEK IN A TIGHTENING PRESSURE GRADIENT BETWEEN A DEPARTING HIGH TO THE NORTH AND LOW PRESSURE DRIFTING INTO THE SOUTHEAST CONUS FROM THE ATLANTIC. WINDS/WAVES SUBSIDE AS THE TWO PRESSURE SYSTEMS WEAKEN AND MOVE AWAY BY NEXT WEEKEND.
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&& .TIDES/COASTAL FLOODING...
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TIDAL ANOMALIES WILL INCREASE IN PERSISTENT MODERATE EASTERLY FLOW WEDNESDAY NIGHT-FRIDAY WHICH ALONG WITH A NEW MOON MAY CAUSE COASTAL FLOODING AROUND TIMES OF HIGH TIDE STARTING LATE WEDNESDAY.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 6 PM EDT MONDAY FOR ANZ530>543.
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&& $$ UPDATE...WOODY! PRVS...BAJ/DFH

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