Area Forecast Discussion
Issued by NWS Sterling, VA

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893 FXUS61 KLWX 190900 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 400 AM EST Sun Feb 19 2017 .SYNOPSIS...
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A weakening area of low pressure will move into the Atlantic this morning. High pressure will return this afternoon and tonight. A backdoor cold front will enter the area Monday into Tuesday. Another disturbance will cross the area early Wednesday. High pressure will be located off the southeast coast of the United States towards the end of the week.
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&& .NEAR TERM /THROUGH TODAY/...
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Through the 1 and 2 o`clock hours and continuing past 3am, an east-west arc of precipitation can been seen on radar across the forecast area from near Elkins across metro Washington DC. However, clouds are mainly mid deck, and the associated forcing is soley a packet of vorticity around 500 mb. Have not seen visibility restrictions anywhere, making the radar returns sprinkles. Have worded forecast as such. RAP and HRRR runs through the night have been fairly consistent in drying the precip up before sunrise. Grids follow suit. Heights rise during the daylight hours as an axis of high pressure shifts east today. As a shortwave crosses New England winds become northwesterly. Mixing looks fairly decent, with mean layer gusts in the mid teens (kts). That should offset any cold advection. Guidance temperatures look comparable to yesterday. Will employ a bias-correction to attempt to get cooler readings along the shoreline of the Chesapeake Bay.
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&& .SHORT TERM /TONIGHT THROUGH TUESDAY NIGHT/...
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From tonight through Monday night, a deep layer ridge axis will translate east, cresting over the East Coast of the United States. However, another lobe of vorticity rotates around the trough axis over the Canadian Maritimes, veering winds north/northeast and sending a backdoor cold front toward the Mid Atlantic. The actual cool-down has been challenging to forecast-- placement, timing, and intensity; latest guidance is focusing more on late Monday afternoon/Monday night (northeast Maryland) into Tuesday (down to the Potomac River). Will follow that lead at this time. Aside from temperatures concerns, the period looks mostly sunny and dry. For that matter, the period will also be mild for late February, just not as warm as current. Meanwhile, a deep-latitude, sharply amplified shortwave will be crossing the country. It will be arriving in the Appalachians Tuesday night. It`s hard to discern if there will be any surface reflection. That once again makes precipitation prospects questionable. Have confined PoPs Tuesday afternoon to a slight chance northwest of Charlottesville-DC-Baltimore and lowered PoPs Tuesday night to 20-30 percent areawide. Clouds will be increasing though, beginning on Tuesday.
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&& .LONG TERM /WEDNESDAY THROUGH SATURDAY/...
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Wednesday through the first part of the weekend will continue the unseasonably warm weather. On Wednesday high pressure settles off the Southeast coast and remains there through the early Saturday. Generally dry weather will be the rule but models do show an area of low pressure moving across the Great Lakes region early Thursday that could help draw up sufficient moisture for a few showers then. Meanwhile low pressure develops in the southern Plains Wed and deepens as it moves northeast into the Great Lakes region Friday night. A cold front will extend from this low that will cross the region on Saturday. Ahead of the front will see an decent plume of moisture. Depending on the timing of the cold front on Saturday...there could be sufficient instability around to fire off thunderstorms along the front as it crosses the region. High pressure builds in Saturday night.
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&& .AVIATION /08Z SUNDAY THROUGH THURSDAY/...
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VFR flight conditions will prevail across the terminals. There are a few sprinkles at DC metro TAFs, but these should cease by sunrise. In the wake of this disturbance, northwest winds will increase, with some gusts approaching 20 kt at inland northern terminals (IAD-MRB). Winds will become more northern Monday and northeast Tuesday. Do not anticipate gusty winds, though. Clouds will be sparse through Monday night, when high deck clouds will thicken. Wednesday and Thursday...surface high pressure will be off the southeast coast. Low pressure passing to the north will help draw in clouds on Thursday...with MVFR ceilings possible in scattered showers.
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&& .MARINE...
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Water temperatures remain in the lower 40s. Gradient winds will increase today in the wake of an upper disturbance. However, air temperatures over land will be in the 60s to near 70. Even after modification due to the marine environment, expect a rather sharp inversion, making it challenging for gusts to mix to the surface. If it were to happen, it would be in a nearshore environment. Left the Small Craft Advisory today for the upper tidal Potomac and Baltimore Harbor, which fits the confluence between 20 kt winds aloft and a narrow waterway. Otherwise, Advisory has been cancelled. High pressure builds tonight into Tuesday, making for light winds. The direction will be veering from northwest today to north Monday and eventually northeast Tuesday as a subtle, backdoor cold front settles across the waters. High pressure settles off the southeast coast on Wednesday and continues through the end of the week. Winds expected to remain below 15 kts during the day.
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&& .CLIMATE...
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Very warm temperatures will persist today. Here is the list of records at the climate locations. Sunday Sunday Site Record high min Record high Washington/Reagan 52 in 1981 74 in 1939 Baltimore/BWI 47 in 1976 72 in 1997 Washington/Dulles 46 in 1981 71 in 1997
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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 10 AM this morning to 6 PM EST this evening for ANZ535-538.
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&& $$ SYNOPSIS...HTS NEAR TERM...HTS SHORT TERM...HTS LONG TERM...SMZ AVIATION...HTS/SMZ MARINE...HTS/SMZ CLIMATE...RCM/SMZ

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