Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 250229 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 1029 PM EDT WED SEP 24 2014 .SYNOPSIS... A LOW PRESSURE SYSTEM WILL DEVELOP OFF THE DELMARVA PENINSULA TONIGHT...AND MOVE ACROSS THE WATERS SOUTH OF NEW ENGLAND ON THURSDAY. HIGH PRESSURE WILL FORM OVER THE GREAT LAKES REGION THURSDAY NIGHT...AND REMAIN ACROSS THE NORTHEAST UNITED STATES THROUGH THE WEEKEND. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... ANALYSIS THIS EVENING SHOWS LOW PRESSURE ALONG THE NORTH CAROLINA COAST WHILE THE UPPER-LEVEL LOW ASSOCIATED WITH THIS SYSTEM IS LOCATED OVER SOUTHWEST VIRGINIA. THE UPPER-LEVEL LOW WILL SLOWLY TRACK THROUGH OUR AREA WHILE THE COASTAL LOW TRACKS UP THE MID- ATLANTIC COAST. A POTENT EASTERLY LOW-LEVEL JET WILL CONTINUE TO PUMP IN MOISTURE FROM THE ATLANTIC OCEAN AHEAD OF THE COASTAL LOW. THE UPPER-LEVEL LOW AND COASTAL LOW WILL ALSO STRENGTHEN A BIT AS IT TRACKS NORTHEAST OVER OUR AREA TONIGHT. THE BEST FORCING APPEARS THAT IT WILL LINE UP NEAR THE WASHINGTON AND BALTIMORE METROPOLITAN AREAS TOWARD THE BLUE RIDGE MOUNTAINS...WHERE THE CONVERGENCE OF THE LOW-LEVEL JET LINES UP WITH THE MID-LEVEL FORCING FROM THE UPPER-LEVEL LOW. PWATS ARE PROGGED TO BE OVER ONE STANDARD DEVIATION ABOVE NORMAL...AND THIS WILL CAUSE RAIN TO BE LOCALLY HEAVY OVERNIGHT...ESPECIALLY ACROSS THE AFOREMENTIONED AREAS. WILL CONTINUE WITH THE FLOOD WATCH FOR THE WASHINGTON AND BALTIMORE METROPOLITAN AREAS...BUT HIGH FFG VALUES SUGGEST THAT MOST AREAS MAY JUST HAVE A SOAKING RAIN. THE BAND OF HEAVY RAIN MAY MAKE IT A TIER OF COUNTIES WEST OF THE WATCH...BUT A FLOOD WATCH HAS NOT BEEN ISSUED AT THIS TIME DUE TO HIGH FFG VALUES. RAINFALL AMOUNTS WILL AVERAGE BETWEEN ONE AND TWO INCHES ACROSS THESE AREAS...BUT THERE WILL BE A TIGHT GRADIENT BETWEEN THE HEAVIER RAINFALL AND LITTLE OR NO RAINFALL WEST OF THE BLUE RIDGE MOUNTAINS INTO THE POTOMAC HIGHLANDS. THEREFORE...THE FORECAST STILL REMAINS A BIT UNCERTAIN AT THIS TIME. MIN TEMPS TONIGHT WILL BE IN THE LOWER 60S IN URBAN AREAS AND IN THE MID TO UPPER 50S ELSEWHERE. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH FRIDAY/... RAIN WILL CONTINUE TO LINGER INTO THE MORNING HOURS ACROSS MUCH OF THE AREA BEFORE PULLING OFF TO THE NORTHEAST IN THE EARLY AFTERNOON. WINDS SHOULD CONTINUE TO BE GUSTY FROM THE NE AGAIN ON THURSDAY AS THE LOW DEEPENS AS IT MOVES TOWARDS CAPE COD AND HIGH PRESSURE STARTS TO BUILD OVER THE GREAT LAKES. HIGHS ON THURSDAY WILL BE IN THE UPPER 60S BUT WITH A GUSTY NE WIND WILL MAKE IT FEEL COOLER. THURSDAY NIGHT AND FRIDAY WILL BE FAIR WITH NEAR NORMAL TO SLIGHTLY ABOVE NORMAL TEMPS. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... HIGH PRESSURE WILL DOMINATE THE REGION FRIDAY NIGHT THROUGH SUNDAY MORNING...PROVIDING PLENTY OF SUNSHINE THAT WILL LEAD TO WARM AFTERNOONS AND COMFORTABLE NIGHTS. HIGHS SHOULD REACH 80 IF NOT A FEW DEGREES ABOVE DURING EACH AFTERNOON. A WEAK COLD FRONT COULD DROP IN ACROSS THE REGION LATE SUNDAY INTO SUNDAY NIGHT. LITTLE OR INSUFFICIENT MOISTURE COULD LEAD TO NO PRECIPITATION AHEAD OF AND ALONG THE FRONT. A REINFORCING AREA OF HIGH PRESSURE WILL BUILD BEHIND THE FRONT MONDAY THROUGH TUESDAY. THIS WILL LEAD TO HIGHS REACHING THE UPPER 70S TO NEAR 80. SOME UPPER LEVEL ENERGY MONDAY NIGHT INTO TUESDAY COULD TRY TO WORK SOUTHEASTWARD ACROSS THE REGION. THERE MAY BE JUST ENOUGH UPPER ENERGY TO SUPPORT A COUPLE OF RAIN SHOWERS IN A FEW AREAS...MAINLY IN THE UPSLOPE PORTIONS OF OUR REGION. WE HAVE SLIGHT CHANCE OR CHANCE POPS TO ACCOUNT FOR THIS. SURFACE WINDS COULD BE EAST TO SOUTHEAST WITH HIGH PRESSURE OVER NEW ENGLAND. && .AVIATION /03Z THURSDAY THROUGH MONDAY/... RAIN WILL CONTINUE TO AFFECT THE TERMINALS TONIGHT INTO THURSDAY MORNING. CIGS/VSBYS WILL DROP TO MVFR/IFR LEVELS AS MOISTURE FROM THE ATLANTIC OCEAN MOVES IN. NORTHEAST WINDS WILL SLOWLY BACK TO THE NORTH TONIGHT WITH GUSTS AROUND 15 KNOTS EXPECTED. NORTHERLY WINDS WILL CONTINUE THURSDAY AND CIGS/VSBYS WILL SLOWLY IMPROVE DURING THE LATE MORNING AND AFTERNOON HOURS. HIGH PRESSURE WILL BUILD OVER THE TERMINALS THURSDAY NIGHT INTO FRIDAY. AREAS OF FOG ARE POSSIBLE OVERNIGHT THURSDAY INTO FRIDAY MORNING. VFR CONDITIONS AT ALL TERMINALS FRIDAY NIGHT THROUGH SATURDAY. WINDS NORTH BECOMING VARIABLE 5 TO 10 KNOTS GUSTS 15 KNOTS FRIDAY NIGHT THROUGH SATURDAY. && .MARINE...
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GUSTY NE WINDS ACROSS ALL THE WATERS THROUGH THURSDAY. A SMALL CRAFT ADVISORY IS IN EFFECT FOR THE WATERS DURING THIS TIME. A SMALL CRAFT ADVISORY CONTINUES THURSDAY NIGHT FOR THE MARYLAND CHESAPEAKE BAY AND LOWER TIDAL POTOMAC RIVER. HIGH PRESSURE WILL BUILD OVER THE WATERS FOR FRIDAY. NO MARINE HAZARDS EXPECTED FRIDAY NIGHT THROUGH SATURDAY.
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&& .HYDROLOGY... LATEST RADAR AND MODEL TRENDS SUGGEST THAT THE HEAVIEST RAIN WILL SET UP NEAR THE CITIES OF WASHINGTON AND BALTIMORE TOWARD THE BLUE RIDGE MOUNTAINS. ONE TO TWO INCHES OF RAIN IS EXPECTED TONIGHT...BUT LOCALLY HIGHER AMOUNTS POSSIBLE. THIS MAY NOT BE QUITE ENOUGH FOR FLOODING BUT STILL ENOUGH UNCERTAINTY NOT TO TAKE DOWN THE FLOOD WATCH ATTM. && .TIDES/COASTAL FLOODING... A POTENT NORTHEAST FLOW THIS EVENING HAS CAUSED TIDAL ANOMALIES TO APPROACH ONE FOOT ABOVE NORMAL. THIS WILL CAUSE WATER LEVELS TO APPROACH THRESHOLDS FOR MINOR TIDAL FLOODING OVERNIGHT INTO THURSDAY MORNING. HOWEVER...LATEST GUIDANCE KEEPS THESE LEVELS BELOW MINOR FLOODING THRESHOLDS...AND WINDS SHOULD BACK TO THE NORTH A BIT OVERNIGHT. GIVEN THESE FACTORS...A COASTAL FLOOD ADVISORY HAS NOT BEEN ISSUED AT THIS TIME. HOWEVER...ANOMALIES THE GUIDANCE HAS UNDERFORECASTED THE CURRENT WATER LEVELS SO THIS WILL HAVE TO BE MONITORED OVERNIGHT. && .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...FLOOD WATCH UNTIL 6 AM EDT THURSDAY FOR DCZ001. MD...FLOOD WATCH UNTIL 6 AM EDT THURSDAY FOR MDZ006-007-009>011-013- 014. VA...FLOOD WATCH UNTIL 6 AM EDT THURSDAY FOR VAZ053-054. WV...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 6 PM EDT THURSDAY FOR ANZ535-536- 538-542. SMALL CRAFT ADVISORY UNTIL 6 AM EDT FRIDAY FOR ANZ530>534-537- 539>541-543.
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&& $$ SYNOPSIS...LEE NEAR TERM...BJL/LEE SHORT TERM...LEE LONG TERM...KLW AVIATION...BJL/KS/KLW MARINE...BJL/LEE/KLW HYDROLOGY...BJL TIDES/COASTAL FLOODING...BJL

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