Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 190129 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 929 PM EDT Tue Oct 18 2016 .SYNOPSIS... High pressure in the western Atlantic will remain in place for the next several days. A cold front will slide southward toward the area Wednesday before lifting back north Thursday. Another, stronger cold front will cross the region Friday. High pressure will return for the weekend. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... High pressure remains centered off the coast this evening. A cold front extends through Lakes Ontario and Erie. Prefrontal clouds are quickly approaching from the NW, although showers are confined closer to the front at this time. The cloud band will slow down however, only affecting northern and western sections of the area overnight. Some of the showers could reach the Allegheny Plateau later tonight, but have trouble advancing to the leeward side. The best chance for patchy fog tonight remains across the Shenandoah Valley and Central Foothills/Piedmont, as they should be mostly clear. Southerly flow may be slightly greater tonight and therefore patchy fog should be confined to river and sheltered valleys. One difference tonight than the past couple is a slower fall in temperatures, with locations that haven`t decoupled still well into the 70s. Will adjust temperatures based on latest trends, but local results may vary depending on decoupling and the advancing clouds. Lows will be in the 60s for most though. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH THURSDAY NIGHT/... The cold front will be in vicinity of the northern Mid-Atlantic region on Wednesday, before lifting back north early Thursday. This will result in overrunning across the region and showers will be possible. While the greatest chance of showers (although scattered at best) will remain in the Highlands and north of I-66/US-50 through Wednesday night, 18Z guidance trended a bit south with shower chances. 12Z SSEO keys in on the east side of the Blue Ridge, although it may be too ambitious trying to produce convection, which seems unlikely given a stable layer around 12kft in forecast soundings. Have therefore only made small increases in POPs. Southerly flow will continue across much of the region and temperatures are expected to climb into the 80s again, however more cloud cover will result in temperatures lower than Tuesday. A strong cold front approaches from the west on Thursday. Mid- level flow will increase across the region and will advect in more moisture from the south. Coverage of showers will increase from west to east Thursday night as a cold front approaches the mountains. Rainfall amounts of less than a quarter inch are expected with the highest amounts across the highlands. There may also be isolated embedded thunder, mainly far western areas. && .LONG TERM /FRIDAY THROUGH TUESDAY/... Guidance is still a bit uncertain about timing of the strong cold frontal passage on Friday but overall they are coming into better agreement with the faster ECMWF timing than they were previously. The ECMWF brings the front through during the day Friday with some showers and perhaps a thunderstorm. Still some more details to be worked out but definitely becoming cooler later in the day behind the front as well as pretty breezy. The rest of the long term period will be dominated by a deep trough which will persist just to our north or northeast through Tuesday. This will keep fast west or northwest flow across the region aloft with much cooler conditions compared to the short term. Highs may be stuck in the 50s some days and frost/freeze is not out of the question if high pressure and calm winds coincides with a night period. This is hard to time since a weak reinforcing cold front will be in the mix which may pass at a bad time for radiational cooling to maximize. && .AVIATION /01Z WEDNESDAY THROUGH SUNDAY/... VFR conditions will continue into tonight. Patchy fog possible again overnight mainly at CHO/IAD, with MRB depending on advancing cloud cover. LAMP points to IFR at CHO, but have limited to MVFR in the TAF due to poor performance last night and less favorable conditions tonight. A stalled frontal boundary will be across the region Wednesday night into Thursday and lower cigs will be possible, however flight restrictions are not expected at this time. The position of the front is a little questionable, but looking like the northern TAF sites will obtain a NW or N wind by late Wednesday. Showers increase in coverage Thursday night and sub- VFR conditions are possible into Friday. Sub-VFR expected at times Friday as a cold front moving through the region brings showers and wind gusts up to 35 knots or so. Winds may persist at times Friday night and Saturday but cigs and vis likely to return to VFR. VFR overall though Sunday-Tuesday but a cold front moving through Monday or Tuesday may briefly feature a reduction to MVFR with more showers at some point. Timing on this feature is highly uncertain. && .MARINE... Southerly winds will continue on the waters tonight, around 10 kt or less. A front will stall and bisect the waters on Wednesday, before lifting north on Thursday morning; therefore winds will be variable but less than SCA criteria. Winds increase a bit out of the south Thursday night ahead of an approaching frontal system and winds may approach SCA conditions. Cold front moving through the region Friday will very likely bring SCA conditions with gales possible later Friday into early Saturday. Winds should relax late in the weekend into early next week as high pressure builds over the region. && .TIDES/COASTAL FLOODING... A south to southwest flow will continue over the waters through Wednesday night. Southerly winds are most likely Thursday into Friday ahead of a cold front. Elevated water levels are expected during this time. DC/Alexandria are trending to peak just below minor flood thresholds for this evening`s high tide, so am holding off on an advisory. Water levels will need to continue to be monitored over the next several days, with the PM high tide being the favored cycle for nearing minor flood threshold at sensitive sites. A potent offshore flow will develop behind a cold front later Friday through the weekend. Blowout tides are possible during this time. && .CLIMATE... A record daily high temperature of 84 degrees was set at Baltimore-Washington International Thurgood Marshall Airport (BWI) near Baltimore MD Tuesday. This breaks the old record of 82 set in 1945...1928 and 1908. Climate records have been kept at BWI since 1950. Additional temperature records for the Baltimore MD area extend back to July of 1872. Two record daily high temperatures were set at Washington Dulles International Airport (IAD) so far this week. A high temperature of 84 degrees Monday broke the old record of 83 set in 1963. A high of 85 degrees on Tuesday broke the old record of 82 set in 2007 and 1963. Climate records have been kept at IAD since November of 1962. Below is a list of record daily warm temperatures for October 19th and 20th. Record daily high temperatures Site 10/19 10/20 DCA 88 (1938) 86 (1969) BWI 82 (1947)* 87 (1969) IAD 83 (1991)* 83 (1969) *also occurred in previous years Record daily warm low temperatures Site 10/19 10/20 DCA 65 (1905) 64 (1885)* BWI 67 (1905) 65 (1910) IAD 60 (2011) 59 (1993) *also occurred in previous years && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...HSK NEAR TERM...ADS/HSK SHORT TERM...ADS/HSK LONG TERM...RCM AVIATION...ADS/MM/RCM MARINE...ADS/MM/RCM TIDES/COASTAL FLOODING...HSK/ADS CLIMATE...DFH is the U.S. government's official web portal to all federal, state and local government web resources and services.