Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 201907 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 207 PM EST Tue Nov 20 2018 .SYNOPSIS... High pressure will nudge into the area tonight, before a strong cold front crosses the region by Wednesday night. High pressure of Canadian origin will build to our north for the remainder of the work week before another low pressure system approaches the area over the weekend. && .NEAR TERM /THROUGH TONIGHT/... Northwest flow from cold advection supporting some wind gusts in the 20s (mph). Clouds have been slow to erode thus far, but the atmosphere dries out considerably by 00z, so feel comfortable with clearing skies by this evening. In the mountains, only webcams showing snow along/just west of the highest terrain. Surrounding the peaks, temperatures still in the mid 30s (or higher). Thus snow accumulation should be localized, and at this point temporally limited. As high pressure nudges east tonight, am looking for a mostly clear night outside of the Appalachians (the mountains will still be mostly cloudy). With decoupling winds, temperatures will be considerably cooler...subfreezing outside of the major downtowns/along the Bay. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... In absence of any synoptically forced feature, Wednesday should be rather benign, albeit a few degrees cooler given cold advection. Shortwave energy crossing the northeast will push a reinforcing cold front through late Wednesday afternoon or Wednesday evening, which will kick up winds and allow arctic air to funnel across the northeast. It may be a struggle for temperatures to rise above freezing on Thursday, especially across northern Maryland. Given its continental origins, there isn`t much moisture associated with the front, and forcing limited as well, so do not expect the frontal passage to be marked by precip. And in the mountains, an inversion around 850 mb will be too strong/low...limiting snow growth. Am carrying just chance snow showers for Wed afternoon/evening. && .LONG TERM /FRIDAY THROUGH TUESDAY/... A upper level ridge will be in place over our region through most of Friday. A surface low at the surface will slowly start to shift northeastward out of the region. Cool and dry weather will continue through the early parts of Friday. Winds will become southerly as the surface high moves northeastwards. The southerly flow will help transport some slightly more moist air into the region. The 00Z Euro and the 12Z GFS both agree that the surface high will settle over New England and the the New England coast. Saturday into Sunday, a frontal boundary will approach from the west with a upper level trough at 500mb. Both GFS and Euro agree that precipitation will start to affect the western parts of our CWA early Saturday morning. The models start to differ on how the surface low that forms over the panhandle of Florida moves northward. The Euro keeps the track closer to the coast while the GFS takes the main low out to sea through the Carolinas. Precipitation will be likely on Saturday and possibly into the early parts of Sunday. The big unknown for this system will be the type of precipitation especially along our mountainous zones. The 850 temperatures hover in the one to 3 degree range especially over the higher elevations while Euro surface temperature output suggest near or slightly below freezing at the surface. This would be freezing rain to a winter mix for most areas around the Blue Ridge and possibly as far east as I-95. The canadian model shows a similar solutions with warm air aloft and could air at the surface. High pressure to the northeast could help dam in cold air over the region. We will be tracking the type of precipitation for Saturday morning and into Sunday. Most precipitation is expected to be out of the region by Sunday morning. Weak high pressure will briefly build into the region on Sunday. On Monday, another frontal boundary is forecast to affect our region. The air mass for this system looks to be much warmer which suggests mainly a rain event. With temperatures warming back into the 50s and the forcing from the boundary could lead to some thunderstorm development but it is too early to tell. && .AVIATION /19Z TUESDAY THROUGH SUNDAY/... VFR flight conditions will prevail through the valid TAF period. Northwest flow will also dominate, with a lull this evening as winds decouple. A reinforcing cold front will kick winds back up Wed late aftn/eve, but forcing seems to be too weak/limited for any precip. It -will- be much cooler for Wed night and Thu. On Friday, high pressure will slowly shift out of the region. Skies will remain mostly clear on Friday with winds becoming southerly. Clouds will build into the region Friday evening. VFR conditions expected. Saturday, a frontal boundary will affect the region. Precipitation will be likely with a wintry mix possible west of I-95 with the best chances over the higher elevation areas. Skies will be mostly cloudy with winds mainly out of the south. SubVFR conditions likely. && .MARINE... Northwest flow behind a cold front have brought winds into the range of Small Craft Advisories this afternoon. Winds will slowly decouple tonight, with a bit of a lull Wed morning. An arctic boundary Wed PM will support more Small Craft winds. Current Advisory Wed afternoon likely will need to be extended into Wed night, and possibly into Thu morning for the open waters of the mid Bay. Northwest flow will gradually decrease during Thanksgiving. On Friday, wind will be out of the south with weak winds aloft. This suggest that small craft advisories won`t be needed at this time. Saturday, precipitation will be likely with winds possibly reaching over 20mph. Small craft advisories will likely be needed. && .CLIMATE... Unseasonably cold weather is looking increasingly likely to briefly take hold of the region on Thanksgiving. Daytime temperatures are likely to stay in the 30s, and it could be the coldest Thanksgiving in over 20 years, depending on the readings at midnight. Here are the benchmark readings to compare this Thanksgiving to: Washington DC area Year High Elapsed 2017 47 1 year 2013 40 5 years 2000 38 18 years 1996 35 22 years 1930 30 88 years The high has not been lower than 30 on Thanksgiving since official temperature record keeping began in 1872. Baltimore MD area Year High Elapsed 2017 44 1 year 2013 38 5 years 2000 37 18 years 1996 33 22 years 1930 31 88 years The high has not been lower than 31 on Thanksgiving since official temperature record keeping began in 1872. Rainfall totals continue to creep upward, with Baltimore setting the annual record already. Here are the current rankings for wettest year on record (through November 18th): Washington DC area (DCA) 1. 61.33 inches (1889) 2. 60.83 inches (2003) 3. 60.09 inches (1878) 4. 58.58 inches (2018) 5. 58.17 inches (1886) Weather records for the Washington DC area have been kept at what is now Ronald Reagan Washington National Airport (DCA) since 1945. Precipitation records observed downtown extend the period of record back to 1871. Baltimore MD area (BWI) 1. 63.18 inches (2018) 2. 62.66 inches (2003) 3. 62.35 inches (1889) 4. 58.98 inches (1979) Weather records for the Baltimore MD area have been kept at what is now Baltimore-Washington International Thurgood Marshall Airport (BWI) since 1950. Precipitation records observed downtown extend the period of record back to 1871. Dulles VA area (IAD) 1. 65.67 inches (2003) 2. 59.17 inches (2018) 3. 59.05 inches (1972) 4. 58.09 inches (1996) 5. 55.43 inches (1979) Weather records have been kept at what is now Washington Dulles International Airport (IAD) since 1960. NOTE: All climate data are considered preliminary until reviewed by the National Centers for Environmental Information (NCEI). && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory until 5 AM EST Wednesday for ANZ530>534- 537>543. Small Craft Advisory from 10 AM to 6 PM EST Wednesday for ANZ530>532-538>540. Small Craft Advisory from 1 PM to 6 PM EST Wednesday for ANZ533>537-541>543. Small Craft Advisory until 6 PM EST this evening for ANZ535- 536. && $$ SYNOPSIS...ADS/HTS NEAR TERM...HTS SHORT TERM...HTS LONG TERM...JMG AVIATION...HTS/JMG MARINE...HTS/JMG CLIMATE...

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