Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 211420 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 1020 AM EDT TUE APR 21 2015 .SYNOPSIS... LOW PRESSURE WILL SLOWLY PIVOT FROM THE GREAT LAKES TOWARD THE SAINT LAWRENCE VALLEY THROUGH THE END OF THE WEEK. A COLD FRONT TRAILING THE LOW WILL CROSS THE MID-ATLANTIC WEDNESDAY. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... RELATIVELY FEW...MINOR CHANGES TO GOING FCST. VERTICALLY STACKED LOW PRESSURE NEAR THE GREAT LAKES WILL BE THE STORY. THE AREA WILL BE IN WESTERLY FLOW. GRADIENT WITH HIGH PRESSURE IN THE DEEP SOUTH WILL LEAD TO BREEZY CONDITIONS. THERE MAY BE CLOUDS AT TIMES AS DISTURBANCES RIPPLE THROUGH THE FLOW. DESPITE CAA BEHIND THE FRONT...DOWNSLOPING WILL ALLOW TEMPERATURES TO RISE BACK INTO THE 60S OUTSIDE THE MOUNTAINS...PERHAPS NEAR 70 IN THE EAST. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/... ANOTHER COLD FRONT WILL BE LOCATED NW OF THE AREA TONIGHT AND ITS APPROACH SHOULD BE SLOW. THERE MAY BE ENOUGH MOISTURE AND LIFT FROM AN EMBEDDED DISTURBANCE TO PRODUCE SOME SHOWERS IN THE POTOMAC HIGHLANDS...BUT DOES NOT LOOK LIKE THE MOISTURE MAKES IT EASTWARD WITH WESTERLY FLOW IN PLACE. THERE IS SOME SPREAD IN LOW TEMP GUIDANCE. TOOK A LARGE BLEND TO SMOOTH DIFFERENCES... RESULTING IN MINS IN THE 40S. THE FRONT WILL GET A PUSH INTO THE AREA ON WEDNESDAY AS A STRONGER SHORTWAVE ROTATES AROUND THE LOW. FAIRLY GOOD AGREEMENT ON ITS PASSAGE...SO A BUMP IN POPS. EXPANDED SLIGHT CHANCE THUNDER WORDING TO MOST AREAS EAST OF THE HIGHLANDS...AS FORECAST SOUNDINGS INDICATE NARROW CAPE PROFILES DEEP ENOUGH TO PRODUCE THUNDER. EXPECT THE SHOWERS WILL PRODUCE SOME GUSTY WINDS AND PERHAPS SMALL HAIL. WINDS WILL BE FAIRLY STRONG OUTSIDE OF SHOWERS AS WELL. HIGH TEMPERATURES A LITTLE TRICKY DEPENDING ON TIMING OF FRONT/SHOWERS. PERHAPS ONLY 50S IN THE WEST...BUT NEAR 70 IN THE SE. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... THERE IS A CHANCE OF A FEW RAIN SHOWERS ACROSS SOUTHERN MARYLAND AND THE CHESAPEAKE BAY WEDNESDAY NIGHT AS A BUILDING RIDGE OF HIGH PRESSURE FROM THE MIDDLE MISSISSIPPI VALLEY GRADUALLY PUSHES A COLD FRONT THROUGH THE REGION. A SLIGHT UPSLOPE COMPONENT TO THE WIND MAY BE ENOUGH TO VOUCH FOR A FEW LIGHT RAIN OR SNOW SHOWERS MIXED ALONG THE HIGHER RIDGE TOPS OF THE NORTHERN AND CENTRAL POTOMAC HIGHLANDS. LOWS WEDNESDAY NIGHT WILL DROP DOWN TO THE LOWER TO MIDDLE 30S IN THE HIGHER POTOMAC HIGHLANDS TO THE MIDDLE 40S IN SOUTHERN MARYLAND AND ALONG THE CHESAPEAKE BAY. DURING THE DAY THURSDAY AND INTO THURSDAY NIGHT...HIGH PRESSURE WILL CONTINUE TO BUILD ACROSS THE REGION...MAKING ITS WAY INTO THE CAROLINAS BY LATE THURSDAY NIGHT. FOR THE MOST PART...CONDITIONS WILL BE DRY BUT SOMEWHAT BREEZY DURING THE DAY THURSDAY. THERE IS A SLIGHT CHANCE FOR A BRIEF UPSLOPE RAIN OR PERHAPS SNOW SHOWER IN THE POTOMAC HIGHLAND THURSDAY INTO THURSDAY EVENING. NO ACCUMULATION EXPECTED. HIGH TEMPERATURES THURSDAY MAY ONLY MAKE IT TO THE UPPER 50S IN MOST LOCATIONS...ABOUT 10 DEGREES BELOW NORMAL. LOWS THURSDAY NIGHT SHOULD BOTTOM OUT IN THE MIDDLE 30S TO NEAR 40 IN MOST PLACES. THIS IS ALSO BELOW NORMAL. LONG TERM PERIOD WILL BE DOMINATED BY A COLD UPPER-LEVEL LOW PRESSURE SYSTEM STALLED OVER THE NORTHEASTERN CONUS...WITH PERSISTENT CHILLY WEST OR NORTHWEST FLOW OVER THE REGION. A TROUGH MAY BRING SOME PRECIPITATION TO THE AREA SATURDAY AND SATURDAY NIGHT...PERHAPS A LIGHT MIX OF RAIN AND SNOW TO THE POTOMAC HIGHLANDS WHERE LOWS SATURDAY NIGHT WILL BOTTOM OUT IN THE LOWER TO MIDDLE 30S. OTHER THAN THAT...MUCH OF THE REGION WILL BE DRY. TEMPERATURES WILL BE WELL BELOW NORMAL /I.E. 10-15 DEGREES BELOW NORMAL/ THROUGH THE PERIOD WITH HIGH STRUGGLING TO GET OUT OF THE 50S AND LOWS IN THE UPPER 30S TO 40S. && .AVIATION /14Z TUESDAY THROUGH SATURDAY/... MAINLY VFR CONDITIONS THROUGH WEDNESDAY. WESTERLY WINDS WILL GUST TO 25 KT TODAY...WITH THE HIGHEST WINDS IN THE MIXED LAYER AVBL IN THE MORNING. ANY CIGS WOULD BE ABOVE 6000 FT. WINDS DIMINISH TONIGHT ONLY TO INCREASE AGAIN WED...WITH SOME 30 KT GUSTS POSSIBLE. A COLD FRONT WILL PASS DURING THE DAY WITH SHOWERS/ISOLD STORM WITH BRIEF VSBY REDUCTIONS POSSIBLE AND A WIND SHIFT FROM S TO W. MVFR OR IFR CONDITIONS POSSIBLE WEDNESDAY NIGHT...MAINLY AT MTN...BWI...AND DCA...DUE TO A CHANCE OF LINGERING RAIN SHOWERS. VFR CONDITIONS THURSDAY AND THURSDAY NIGHT. WINDS LIGHT AND VARIABLE WEDNESDAY NIGHT THEN WEST TO NORTHWEST AROUND 10 KNOTS WITH HIGHER GUSTS THURSDAY AND THURSDAY NIGHT. WLY FLOW 10 KT OR SO W/ MAINLY VFR EXPECTED THU-SAT. && .MARINE... SCA FOR ALL WATERS TODAY. HIGHEST WINDS /25-30 KT/ AVBL IN MIXED LYR THIS MRNG...BUT AT LEAST 20 KT THRUT THE DAY. WINDS DIMINISH TONIGHT BUT INCREASE OUT OF THE SW AHEAD OF COLD FRONT WED. WIND SHIFT TO W LATE. GUSTS MAY APPROACH GALES ON BOTH SIDES OF THE FRONT...BUT HAVE CAPPED AT 30 KT FOR NOW. SHOWERS/ISOLD STORMS ALONG FRONT. NO MARINE HAZARDS WEDNESDAY NIGHT. SMALL CRAFT ADVISORIES ARE POSSIBLE THURSDAY. NO MARINE HAZARDS THURSDAY NIGHT. LIGHT FLOW BELOW SCA CRITERIA LIKELY FRIDAY THROUGH SATURDAY. && .TIDES/COASTAL FLOODING... ANOMALIES STILL RUNNING ABOVE NORMAL. HV BEEN ABLE TO DROP ADVY FOR THE GOING HIGH AT ANNAPOLIS. GAUGE JUST TOUCHED ADVY LVL. NO OTHER ISSUES ON THE BAY. FOR THE POTOMAC...THE TIDAL ANOMALY HAS RESULTED IN REACHING ADVY THRESHOLD AT ALEXANDRIA AND SW DC...WITH THE TIME OF HIGH TIDE 30 TO 60 MIN AWAY. HV JUST ISSUED AN ADVY THRU 1PM. WLY WINDS WONT BE TOO EFFECTIVE AT DRAINING WATER OUT OF THE BAY. BUT...THE PM TIDE IS THE LOWER OF THE TWO ASTRONOMICALLY. WE MAY BE ABLE TO SQUEEK OUT A TIDE CYCLE WITHOUT ANY MINOR INUNDATION. NOT SURE. AM ALSO UNCERTAIN IF WE WILL GET RID OF ENOUGH WATER BY THE WED AM CYCLE TO NOT REPEAT THE PROCESS THEN. WILL HAVE SOMETHING TO MONITOR FOR THE NEXT COUPLE OF DAYS...AS WATER LEVELS WILL AT THE VERY LEAST REMAIN ELEVATED. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...COASTAL FLOOD ADVISORY UNTIL 1 PM EDT THIS AFTERNOON FOR DCC001. MD...NONE. VA...COASTAL FLOOD ADVISORY UNTIL 1 PM EDT THIS AFTERNOON FOR VAZ054. WV...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 10 PM EDT THIS EVENING FOR ANZ530>543. SMALL CRAFT ADVISORY FROM 9 AM TO 8 PM EDT WEDNESDAY FOR ANZ530>543. && $$ SYNOPSIS...ADS NEAR TERM...ADS/HTS SHORT TERM...ADS/HTS LONG TERM...KLW/DFH AVIATION...ADS/HTS/KLW MARINE...ADS/HTS/KLW TIDES/COASTAL FLOODING...HTS

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