Area Forecast Discussion
Issued by NWS Sterling, VA

Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
350 FXUS61 KLWX 141943 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 243 PM EST Sun Jan 14 2018 .SYNOPSIS...
-- Changed Discussion --
Canadian high pressure will settle over the eastern U.S. through tonight before sliding to our east Monday. A clipper system will bring a cold front through the area Tue night into Wednesday. Low pressure will develop offshore late Wednesday into Thursday before high pressure settles to our south late in the week.
-- End Changed Discussion --
&& .NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
Canadian high pressure will continue to build toward the area this afternoon...bringing dry and cold conditions despite sunshine. High pressure will remain overhead tonight. Light winds and dry air will provide a good setup for radiational cooling. There will be some high clouds ahead of an upper-level trough over the Great Lakes into the southeastern CONUS. This may prevent radiational cooling to some extent...but current thinking is that the cloud deck will be thin. Therefore...min temps are expected to range from the single digits in colder valleys and rural areas to the teens across most other locations.
-- End Changed Discussion --
&& .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
-- Changed Discussion --
A potent northern stream system will cause upper-level low pressure to dig into the northern Plains and western Great Lakes Monday. This will continue to carve out an upper-level trough to our west. Shortwave energy and a jetmax well ahead of the upper-level low will pass through our area Monday while high pressure slides just to our east. The jetmax will have decent forcing with it since our area will be in its left-exit region. This will back the low-level flow...resulting in isentropic lift across much of the area. Since there is plenty of dry air in place most locations should end up dry with just some clouds. However...flurries and perhaps even a period of very light snow cannot be ruled out across eastern areas where there will be a little more moisture to work with. The best chance for a period of very light snow will be near the Bay from mid-morning through the afternoon and it could coat the ground. Confidence in this is low at the this time since the deeper moisture is expected to remain well off to the east. The current forecast mentions a chance for flurries but this will have to be monitored closely. Chilly conditions will continue with highs in the upper 20s and lower 30s near Washington and Baltimore. The shortwave energy and jetmax will move off to the north Monday night. A cold front will approach from the Ohio Valley and a southerly flow will allow for relatively milder conditions compared to Sunday night...but it will still be cold. A potent upper-level low will slowly pass through the eastern Great Lakes Tuesday through Tuesday night. This system will be strong enough for surface low pressure to develop over the same area. The upper-level trough axis associated with this system will swing closer towards neutral tilt during this time. A strengthening jet will cause a band of precipitation to develop Tuesday and it will slowly move south and east into our area. Exact timing remains uncertain due to divergence in the guidance. For now...the timing of snow is a blend between the faster GFS and the slower ECMWF/NAM which is close to the GEFS which lies in between. This means that the best chance for accumulating snow Tuesday morning will be in the Potomac Highlands...but it may make a run south and east toward the I-95 Corridor by Tuesday evening. There is a better chance for snow later Tuesday night near and south/east of the I-95 corridor.
-- End Changed Discussion --
&& .LONG TERM /WEDNESDAY THROUGH SUNDAY/...
-- Changed Discussion --
Light snow may be ongoing Wednesday as an upper trough and jet max aloft move across the area and induce cyclogenesis off of the eastern US coastline. Much of the precipitation tied to the coastal low now appears to remain offshore, however upper level forcing and jet dynamics still favor a period of snow Wednesday. Some accumulation is likely, although timing and amounts are still uncertain as non-trivial model differences still exist. Very cold and blustery conditions will then again follow behind the departing system for later Wednesday, Wednesday night, and lasting into Thursday morning. High pressure will then build south of the region from Thursday through Saturday, which will promote southerly flow and moderating temperatures over the Mid-Atlantic. A fast moving upper level shortwave will race across the northern tier of the country and into the northeast on Friday, and this may bring a chance of some light precipitation. By next Sunday, a low pressure system will be developing in the central/southern Plains states and eject northeastward towards the Great Lakes. This will further increase warm air advection and southerly flow across the area. Temperatures during the extended period will start quite cold with highs in the 20s on Wednesday, and lows in the teens Wednesday night. A gradual moderation is expected for the end of the week and weekend with 30s for highs Thursday, 40s Friday, and then likely breaking into the 50s by Saturday and Sunday.
-- End Changed Discussion --
&& .AVIATION /19Z SUNDAY THROUGH FRIDAY/...
-- Changed Discussion --
VFR conditions are expected through tonight. Warm advection behind high pressure sliding east Monday will cause lower clouds to develop across the eastern terminals. MVFR conditions are likely for KBWI and KMTN...KDCA and possible for KIAD. A few flurries are possible Monday across the same terminals. MVFR cigs may continue Monday night across the eastern terminals. A cold front along with low pressure will cause a band of snow to develop Tuesday morning to the north and west. The snow will slowly slide south and east...impacting the terminals later Tuesday and Tuesday night. The snow may hang around for much of Wednesday as well...especially across the eastern terminals. Exact timing is uncertain but confidence has increased for a period of accumulating snow during this time. Primarily VFR will return for Wednesday night through Friday, although some light precipitation is also possible Friday. Gusty northwest winds are also expected to develop Wednesday into Thursday.
-- End Changed Discussion --
&& .MARINE...
-- Changed Discussion --
A north to northwest flow will continue through the rest of the afternoon. Wind speeds will gradually decrease during this time. A Small Craft Advisory remains in effect until 5 pm. High pressure will remain over the waters tonight...but a weak pressure surge will cause northerly winds to channel down the Bay/lower Tidal Potomac River. A Small Craft Advisory remains in effect for the lower Tidal Potomac River and Maryland Chesapeake Bay south of Smith Point. Weak high pressure will remain just offshore Monday through Tuesday night. Winds should remain below SCA criteria during this time. Sub-SCA conditions are likely Wednesday into Thursday behind a departing low offshore. Another period of SCA conditions are possible on Friday with a weak system.
-- End Changed Discussion --
&& .LWX WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory until 5 PM EST this afternoon for ANZ530>533-535-536-538>542. Small Craft Advisory until 6 AM EST Monday for ANZ534-537-543.
-- End Changed Discussion --
&& $$ SYNOPSIS...BJL NEAR TERM...BJL SHORT TERM...BJL LONG TERM...BJL/MM AVIATION...BJL/MM MARINE...BJL/MM

USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.