Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 212216 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 616 PM EDT TUE OCT 21 2014 .SYNOPSIS... A COLD FRONT WILL MOVE THROUGH THE MID ATLANTIC REGION THIS EVENING. LOW PRESSURE WILL PERSIST ALONG THE COAST THROUGH THURSDAY. HIGH PRESSURE WILL RETURN FOR THE END OF THE WORKWEEK AND INTO THE WEEKEND. && .NEAR TERM /THROUGH WEDNESDAY/...
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UPDATE...PRESSURE SURGE MOVING ACROSS THE MID-ATLANTIC AND TOWARDS THE WATERS LATE THIS AFTERNOON. SEE MARINE SECTION. DEVELOPING SURFACE LOW PRESSURE WILL MOVE THROUGH THE REGION LATE THIS AFTERNOON AND EVENING...THEN OFFSHORE OVERNIGHT. BROAD CLOSED UPPER LOW OVER THE LOWER GREAT LAKES WILL ALSO DROP INTO THE MID- ATLANTIC REGION BY THIS EVENING...AND BECOME BETTER ORGANIZED AS IT MOVES INTO THE TIDEWATER REGION OVERNIGHT. COMBINATION OF COOL AIR ALOFT...AN APPROACHING COLD FRONT AND MARGINAL SURFACE INSTABILITY IS PRODUCING SCATTERED RAIN AND SHOWERS OVER THE SHENANDOAH VALLEY...POTOMAC HIGHLANDS AND UPSTREAM ACROSS WV/PA AND OHIO LATE THIS AFTERNOON. WITH AROUND 500 J/KG OF SBCAPE...WILL HAVE ENOUGH INSTABILITY FOR SOME ISOLATED HEAVIER SHOWERS AND PERHAPS A FEW THUNDERSTORMS LATE THIS AFTERNOON AND EVENING. AFTERNOON HIGH TEMPS ARE PRIMARILY IN THE 60S...WITH A FEW 70S NOTED IN THE VA PIEDMONT. COOLER TEMPS OVER THE MOUNTAINS WHERE CLOUD COVER AND RAIN IS KEEPING TEMPS IN THE UPPER 50S. RAIN WILL CONTINUE OVERNIGHT AS THE SURFACE AND UPPER LOWS MOVE JUST TO THE EAST AND SOUTHEAST OF THE FORECAST AREA. BASIN WIDE RAIN AMOUNTS WILL LIKELY BE A QUARTER OF AN INCH OR LESS OVERNIGHT...BUT SOME LOCAL AREAS MAY SEE HIGHER AMOUNTS WITH LOCALIZED PERIODS OF MORE MODERATE RAINFALL. STEADY BREEZE AROUND 5-10KT FROM THE NW CONTINUES AS THE PRESSURE GRADIENT AROUND THE BACK SIDE OF THE SURFACE LOW INCREASES. LOWS TONIGHT RANGE FROM THE LOW 40S IN THE HIGHLANDS TO THE LOW 50S ALONG AND EAST OF I-95.
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&& .SHORT TERM /WEDNESDAY NIGHT/... SURFACE LOW PRESSURE MOVES OFFSHORE AND BEGINS TO STRENGTHEN AS IT REACHES THE GULF STREAM. WINDS STRENGTHEN TO AROUND 15-20 MPH WITH HIGHER GUSTS AS THE PRESSURE GRADIENT BETWEEN THE STRENGTHENING LOW AND HIGH PRESSURE OVER THE OHIO VALLEY. WRAPAROUND RAINFALL LIKELY AT TIMES OVER EASTERN MD AND PORTIONS OF VA. UPSLOPE RAIN WILL DEVELOP OVER THE POTOMAC HIGHLANDS AND CONTINUE WEDNESDAY NIGHT. LOOKS LIKE OVERNIGHT TEMPS WILL FAVOR LIQUID RAIN OVER MOST OF THE HIGHLANDS...BUT THE HIGHEST ELEVATIONS IN GRANT...PENDLETON AND HIGHLAND MAY SEE SNOW MIXED IN. LOW TEMPS IN THE 40S ACROSS MOST OF THE FORECAST AREA. && .LONG TERM /THURSDAY THROUGH TUESDAY/... BLUSTERY CONDITIONS WILL CONTINUE INTO THE DAY THURSDAY AS SURFACE LOW PRESSURE SLOWLY SLIDES UP THE NEW ENGLAND COAST. DOWNSLOPING OF NORTHEASTERLY WINDS WILL ELIMINATE POPS LOCALLY DURING THE DAY THURSDAY EVERYWHERE EXCEPT THE POTOMAC HIGHLANDS...WHERE UPSLOPE RAIN IS POSSIBLE...AND THE FAR NORTHEASTERN PORTION OF THE CWA ALONG THE CHESAPEAKE BAY. HIGH PRESSURE WILL BEGIN TO FILL IN THURSDAY NIGHT AND WINDS WILL BE WEAKER FRIDAY. THE REST OF THE LONG TERM PERIOD WILL SEE QUIET/DRY WEATHER AS BROAD SURFACE HIGH PRESSURE MOVES OVERHEAD AND UPPER LEVEL RIDGING KEEPS PLENTY OF SUNSHINE ACROSS THE AREA. EXPECT TEMPS THIS WEEKEND TO BE RIGHT AROUND NORMAL...WITH HIGHS MOSTLY IN THE MID-60S...AND TEMPS EARLY NEXT WEEK TO BE JUST A FEW DEGREES ABOVE NORMAL. && .AVIATION /22Z TUESDAY THROUGH SUNDAY/... SCATTERED AREAS OF RAIN ARE DEVELOPING TO THE WEST...AND WILL MOVE INTO THE WASHINGTON/BALTIMORE TERMINALS BY THIS EVENING. PERIODS OF MVFR VSBYS LIKELY WITH RAIN. CIGS LOWER TO MVFR TONIGHT. PERIODS OF IFR PSBL AS WELL AS LOW PRESSURE MOVES ACROSS THE REGION BRINGING ADDITIONAL RAINFALL. LIGHT WESTERLY WINDS THIS AFTN AND EVENING...BECG NW AND INCREASING TO AROUND 10KT OVERNIGHT. LOWER CIGS EXPECTED TO PERSIST WEDNESDAY...AND PERIODIC RAINFALL WILL BE POSSIBLE. GUSTY NW WINDS EXPECTED...UP TO 20-25KT BY THE AFTERNOON. THU...VFR. NW WINDS GUSTING TO 20-25KT. FRI...VFR. NW WINDS AROUND 1OKT. CONFIDENCE IS LOW IN THE OCCURRENCE OF AVIATION HAZARDS OVER THE WEEKEND AS HIGH PRESSURE BUILDS IN. CLDY WED NGT BUT CIGS XPCTD TO BE VFR. BRZY NW WINDS XPCTD WED NGT AND THU. VFR/NO PROBS FRI AND SAT. && .MARINE...
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UPDATE...PRESSURE SURGE HEADING TOWARDS THE WATERS AS A COLD FRONT MOVES THROUGH THE I-95 CORRIDOR. NW WINDS BEHIND THE FRONT HAVE RESULTED IN GUSTS AROUND 20KTS. A TIGHT PRESSURE GRADIENT WILL MOVE INTO THE REGION TONIGHT. A SCA IS NOW IN EFFECT FOR THE WATERS. PREVIOUS DISCUSSION... RAIN WILL MOVE INTO THE WATERS LATE THIS AFTERNOON AND EVENING...WITH POTENTIAL FOR A FEW THUNDERSTORMS. WINDS BECOME N-NW AND INCREASE OVERNIGHT...WITH SCA GUSTS LIKELY BY EARLY WEDNESDAY MORNING. POTENTIAL CONTINUES FOR GALES WEDNESDAY NIGHT AS LOW PRESSURE STRENGTHENS OFF THE NJ/DELMARVA SHORE. MODEL FORECASTS ARE MARGINAL FOR GALES...SO FOR NOW OPTED TO EXTEND SCA THROUGH WEDNESDAY NIGHT WITH GUSTS LIKELY TO REACH 30KT IN SOME PARTS OF CHES BAY AT LEAST. A SMALL CRAFT ADVISORY WILL LIKELY BE NEEDED THURSDAY THROUGH FRIDAY AND POSSIBLY INTO FRIDAY NIGHT IN GUSTY NORTHEASTERLY WINDS AS LOW PRESSURE MOVES UP THE NORTHEAST COAST. WINDS MAY APPROACH GALE FORCE THURSDAY AFTERNOON OVER THE WATERS...THOUGH CURRENTLY THINK THEY WILL STAY MOSTLY IN THE MID TO UPPER 20 KNOT RANGE.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY FROM 11 PM THIS EVENING TO 6 AM EDT THURSDAY FOR ANZ530>534-538>543. SMALL CRAFT ADVISORY UNTIL 6 AM EDT THURSDAY FOR ANZ535>537.
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&& $$ UPDATE...HAS SYNOPSIS...KS NEAR TERM...KS SHORT TERM...KS LONG TERM...CEB AVIATION...KS/CEB MARINE...KS/CEB

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