Area Forecast Discussion
Issued by NWS Sterling, VA

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173 FXUS61 KLWX 191953 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 253 PM EST Sun Feb 19 2017 .SYNOPSIS...
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High pressure will build from the west through tonight. A backdoor cold front will enter the area Monday into Tuesday. A weak disturbance will cross the area Tuesday night. High pressure will be located off the southeast coast of the United States for the second half of the week.
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&& .NEAR TERM /THROUGH TONIGHT/...
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High pressure extends from the Great Lakes to the central Gulf coast this afternoon. The bulk of cloud cover has moved out of the area, with stratus banked along the west side of the Appalachians. Temperatures have risen into the 60s and 70s in most locations. Wind gusts have been somewhat spotty, but with occasional gusts over 20 mph. These gusts will subside with sunset. For tonight, the high will edge eastward while a mid-level trough digs over New England. Western areas may have a better chance of decoupling, and 30s will be more likely there. Elsewhere will remain in the 40s. Only some scattered mid and high level clouds are expected.
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&& .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
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A backdoor cold front will slip southwestward on Monday. Latest guidance hasn`t deviated significantly in the temperature forecast, but the ultimate gradient may be much tighter than currently in the grids between lower to mid 50s in northeast MD and around 70 in central VA. Clouds should remain limited to the mid and high level variety during the day. An upslope/overrunning component will develop by Monday night, which could lead to some lower cloud development over the mountains. Expect Monday night to be one of the cooler nights this week as drier air seeps in with light winds and few clouds. Ridge axis aloft will move over the area Tuesday morning while the surface high extends along the coast. Despite developing southerly flow, mixing will be poor, and thus Tuesday is still expected to be the coolest day this week. Of course that is relative, with high temperatures still running at least 10 degrees above normal. Clouds will begin to increase through the day. A shortwave trough will approach Tuesday night. However, that`s where the bulk of the forcing and moisture will be located, with only a hint of a surface trough reflection. Computer models are a little more aggressive with QPF than last night`s system as the narrow ribbon of forcing/moisture traverses the area, but still only looking at less than a tenth inch where rain does fall. The highest chances will be north/west of DC. Clouds should keep lows in the 40s.
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&& .LONG TERM /WEDNESDAY THROUGH SUNDAY/...
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Upper-level ridging will traverse the area Wednesday into early Thursday as surface high pressure remains stationed off the southeast coast. Continued southwesterly flow will keep temperatures quite mild by late February standards, and perhaps near record levels (especially for warm lows and/or in the IAD area; see Climate section below). As strong low pressure develops over the central Plains late Thursday into Friday, a warm front will develop and push to the north of the area, but may also lead to increasing clouds and potential bouts of rain. The low will track across the Great Lakes Friday night into Saturday bringing a cold front through the area. Most of the forcing will likely be just north and west of the area, but showers are still possible, as are thunderstorms if the front crosses near peak heating Saturday (exact timing still in question). Temperatures will cool closer to seasonable levels by the second half of the weekend behind the front.
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&& .AVIATION /19Z SUNDAY THROUGH FRIDAY/...
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VFR flight conditions will continue to prevail across the terminals through the TAF period. Occasional gusts to 20 kt will subside with sunset. Relatively clear and calm tonight. LAMP guidance suggests fog at CHO, but am not seeing much other support to include anything in the TAF now. Winds will become more northerly Monday and northeast Monday night. Do not anticipate gusty winds, though. Clouds will be sparse until Monday night. Some lower VFR or MVFR cigs could develop at or near the western terminals (MRB, CHO, IAD), but confidence is low. No issues expected Tuesday. A weak trough will cross the area Tuesday night. Any showers appear to be scattered and light and thus do not anticipate widespread cig/vsby issues. Patchy MVFR possible Wed AM mainly near outlying terminals...then mainly VFR expected through Thursday. Flow generally SWLY AOB 10 kts.
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&& .MARINE...
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Despite morning indications of efficient mixing of 20 kt gusts nearshore and on the narrower waterways, such gusts have been very sporadic into this afternoon. Will allow SCA to continue with occasional gusts ongoing, but it may be able to be cancelled early. Winds aloft increase this evening, but models suggest a sharp low level inversion by that time. High pressure builds from the west tonight into Tuesday. Overall winds should be light, although there may be periods with 10-15 kt during the daytime hours. The direction will be veering to north Monday, northeast Monday night as a subtle, backdoor cold front settles across the waters, and perhaps southerly by late Tuesday as high pressure moves east. With high pressure ridging across the region Wednesday into Thursday and non-channeling flow of mild air over cooler waters, winds will likely stay below Small Craft Advisory criteria.
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&& .CLIMATE...
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Unseasonably mild temperatures are being observed across the region today, and are forecast again later in the week. Below is a list of record daily warm temperatures for today and the next potential near-record warm spell later this week. February 19th Site Record High Record Warm Low DCA 74 (1939) 52 (1981) SAFE: low this morning was 49 BWI 72 (1997) 47 (1976) IAD 71 (1997) 46 (1981) February 22nd DCA 77 (1874) 60 (1874) BWI 74 (1874) 51 (1874) IAD 71 (1991) 52 (1981) February 23rd DCA 78 (1874) 51 (1922) BWI 78 (1874) 52 (1874) IAD 73 (1985) 51 (1975)
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&& .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory until 6 PM EST this evening for ANZ530- 531-535-536-538-542. && $$ SYNOPSIS...ADS NEAR TERM...ADS SHORT TERM...ADS LONG TERM...DFH AVIATION...ADS/DFH MARINE...ADS/DFH CLIMATE...DFH

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