Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 201419 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 1019 AM EDT Wed Jul 20 2016 .SYNOPSIS...
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High pressure will build southeast across the area through this evening before drifting offshore through Thursday. A cold front will pass to the north Friday night with high pressure then in control across the eastern states through Monday. A cool front looks to enter the area Monday night and linger just south of the area into the midweek.
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&& .NEAR TERM /THROUGH TONIGHT/...
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As of 9am, upper 50s to low 60s dewpoints continue to spread south across the area in a light north wind. A weak boundary looks to linger over central Virginia through midday where dewpoints will remain in the mid 60s. Dry across the area today with the exception of an isolated shower or thunderstorm possible across central Virginia into extreme southern Maryland this afternoon into this evening...but even across these areas most of the time will be dry. High pressure will remain overhead for tonight...bringing dry and comfortable conditions. Min temps mid 60s inland (around 60s west of the Blue Ridge) and 70s near shore (water temps in the low 80s).
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&& .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... High pressure will weaken and move offshore Thursday into Thursday night. A return flow will allow for slightly more humid conditions...and max temps will be a few degrees hotter compared to Wednesday with most areas topping off in the upper 80s to lower 90s. Min temps Thursday night will range from the 60s in the Potomac Highlands and portions of the Shenandoah Valley to the lower and middle 70s near Washington and Baltimore. High pressure over the Atlantic will dominate the weather pattern for Friday and Friday night. A subtropical ridge will also begin to edge closer to the area...with the center of the ridge remaining over the central Conus. The higher heights along with a southwest flow will cause unseasonably hot conditions for Friday. Max temps will be in the middle to upper 90s across most locations...but cooler in the mountains. Do think that there may be enough of a westerly component to the low-level flow for dewpoints to mix down into the lower to middle 60s during peak heating. If this occurs...then heat indices around 100 degrees are expected. However...higher dewpoints may cause heat indices around 105 degrees and this cannot be ruled out at this time. Very warm and humid conditions will persist for Friday night. && .LONG TERM /SATURDAY THROUGH TUESDAY/... Heat will be the primary concern for the extended forecast. Area will be influenced by westerly flow aloft, an artifact of the broad ridge stretching across the Conus. Temperatures at 850 mb will solidly reach 20C, and may even reach 22C. As a result, highs will be well into the 90s if not approaching 100F. Inherently there will be plenty of available instability given the forecast heat. However, skill in forecasting placement and timing of shortwaves in the extended forecast quite low. That will be the key in determining which days have a thunderstorm threat. If the ingredients were to assemble properly, an organized event will be a possibility. Will refrain from those details at this time. A cold front forecast to arrive by the end of the period. The upper level pattern changes little though, so its effect may be minimal. && .AVIATION /14Z WEDNESDAY THROUGH SUNDAY/...
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VFR conditions prevail under high pressure that builds today and shifts offshore Thursday. Patchy fog may briefly reduce vsbys during the early morning hours each day. A cold front passes north of the area Friday night with chance thunder. VFR anticipated this weekend under high pressure with a boundary stalled south of the area. Its too early to determine whether there will be a thunder threat.
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&& .MARINE...
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A weak cold front will continue to shift south to southern MD Chesapeake Bay waters through the rest of the morning. North winds expected to peak at 15 knots or less. This boundary will stall near or south of Smith Point today. High pressure will build over the area through tonight and winds will be light. An isolated shower or thunderstorm cannot be ruled out near Smith Point into this evening...but even across this area most of the time will be dry. The high will move offshore Thursday and a return flow will develop. A south to southwest flow will continue for Thursday night through Friday night. Southerly winds may channel up the middle portion of the Bay and Lower Tidal Potomac River...causing winds to possibly reach SCA criteria during this time. Summertime high pressure, with its heat and humidity, will be affecting the waters this weekend. Such a pattern favors southerly channeling late into the evening into the early morning hours.
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&& .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...BAJ/BJL NEAR TERM...BAJ/BJL SHORT TERM...BJL LONG TERM...HTS AVIATION...BAJ/BJL/HTS MARINE...BAJ/BJL/HTS

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