Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 060123 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 923 PM EDT Thu Aug 5 2021 .SYNOPSIS... High pressure will remain over the St. Lawrence Valley to the Ohio Valley through the end of the week. Meanwhile, a series of low pressure systems will track along a stationary front located east of the Mid Atlantic coast. High pressure will shift into the Atlantic Ocean this weekend and remain there through early next week. && .NEAR TERM /TONIGHT/...
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Weak high pressure will preside over the region tonight with light to calm winds and mainly clear skies. Earlier showers and isolated thunderstorm activity has waned with the loss of daytime heating. Patchy fog will be possible overnight west of the Blue Ridge Mountains, primarily near areas that received rainfall. Temperatures tonight should radiate nicely with skies clearing and winds on the calm side. Temperatures by daybreak will range from the upper 50s over the Alleghenies to the low to middle 60s much elsewhere, while the city centers hover around 70.
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&& .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
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Shortwave ridging is expected to bring dry and hot weather on Friday. Temperatures likely break 90 for many areas. Dew points only rise into the upper 50s to low 60s though, so heat indices won`t be much different. So, should just be a warmer than average, but dry, summer day. With the stalled frontal boundary still well to our southeast, and an approaching upper trough from the west, surface low pressure will develop along the coast and slide by to our south through Saturday. This will result in increased cloud cover starting Friday night and continuing into Saturday. Rain chances increase throughout the day Saturday, but am maintaining only chance POPs as the core of precipitation should pass by to our south. A few thunderstorms can`t be ruled out, but the threat for severe weather appears low since much of the region will be on the relatively stable side of low pressure tracking to the east. A marginal flood threat could develop near southern Maryland if some of the wetter guidance were to come to fruition. Lots of uncertainty there though, as the GFS came way down from its 00z solution in the 06z and 12z runs consecutively. Then the ECMWF has trended significantly further west in the 12z run. So, likely we will meet somewhere in the middle here. Have brought southern Maryland into the half inch bin in terms of QPF for the event for now, and will re-evaluate as new guidance comes in. At any rate, precipitation comes to an end Saturday evening and skies will gradually clear out, with lows in the mid 60s expected.
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&& .LONG TERM /SUNDAY THROUGH THURSDAY/... Shortwave begins to depart off the coast by Sunday morning with ridging building in behind. This will result in none to low end PoPs for the end of the weekend into early next week. Ridging across the Great Plains and troughing to the NW and over the Great Lakes and areas further east will play an important role in our potential impacts for the early part of the work week. Temperatures and dew points will increase through the period, this will lead to the potential for Heat Advisories across portions of the area Tuesday and Wednesday. With this type of pattern and being so far out, it is important to remember the impacts of terrain circulation and bay breeze interactions which may pose a threat for us during this period in the form of thunderstorms and localized heavy rainfall. Will continue to monitor any pattern changes for the time frame. && .AVIATION /01Z FRIDAY THROUGH TUESDAY/...
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VFR conditions expected to prevail over the terminals tonight as weak high pressure sits atop the region. As a result, light to calm winds and dry conditions are forecast. Patchy morning fog is possible around MRB/CHO. VFR conditions expected Friday with a ridge of high pressure overhead and light southerly winds at less than 10 knots. Cloud cover and rain chances will increase by Saturday, but uncertainty remains in how low clouds get or how widespread any shower or thunderstorm activity becomes. With high pressure overhead, expect VFR conditions on Sunday and Monday.
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&& .MARINE...
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Weak high pressure will reside over the region tonight through Friday with light southerly breezes and sub SCA conditions prevailing over the waters. Low pressure will track southeast of our waters Saturday into Saturday night, bringing some precipitation to the area as winds turn out of the southeast and remain below SCA thresholds. With a departing low pressure to the NE and high pressure building in from the west, gradient may become tighter thus increasing winds near the surface. As a result, SCA`s are possible Sunday into Monday.
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&& .TIDES/COASTAL FLOODING...
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Anomalies are running a touch high this evening in a light southerly flow regime. As a result, our Annapolis and Southwest D.C. will flirt with Action stage during the overnight high tide cycle. With the expectation for winds to slacken tonight as high pressure takes control, anomalies should level off enough to stave off any tidal flooding concerns. Will continue to monitor this potential threat overnight.
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&& .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...BKF/CJL NEAR TERM...BKF/CJL SHORT TERM...CJL LONG TERM...ADM AVIATION...BKF/CJL/ADM MARINE...BKF/CJL/ADM TIDES/COASTAL FLOODING...BKF

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