Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 201358 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 958 AM EDT Thu Oct 20 2016 .SYNOPSIS... A weak boundary overhead this morning will retreat to the north as a warm front later today. A cold front will approach the area tonight before passing through Friday. An upper-level trough will pass through the area Saturday and high pressure will build into the region for Sunday. A reinforcing cold front will pass through the area Monday with high pressure returning for the middle portion of next week. && .NEAR TERM /THROUGH TONIGHT/...
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A weak boundary remains draped across eastern west Virginia into southern Maryland this morning. Dry conditions are expected the rest of the morning as temperatures rise into the upper 70s and 80s by afternoon. Showers are expected to develop acros sthe Ohio Valley this afternoon. The Mid-Atlantic will be in the warm sector this afternoon and into evening as a strong cold approaches. Hi- res model guidance has the best chance for thunder across the Potomac Highlands this afternoon into evening. Further east...any convection will be hard to come by as an inversion exists at 700mb in the 12Z IAD raob. Little TO no inversion exists at KPBZ. Previous discussion... The boundary will slowly lift north this morning eventually moving off to our north today as a warm front. Southerly winds behind the boundary will continue to usher in unseasonably warm conditions. Max temps will be in the lower to middle 80s across most locations. Morning clouds associated with the boundary will give way to a partly to mostly sunny sky later today. Warm and moist air may cause a couple popup showers to develop this afternoon. The best chance will be across the Potomac and Allegheny Highlands where 500mb heights are a bit lower and a weak surface trough may develop. Even across these areas...most of the time will be dry. A potent cold front will track through the Ohio Valley this evening and eventually into our western areas overnight. An upper-level disturbance associated with the boundary will remain just to our west. Showers are expected to develop along the boundary. The best chance for showers will be west of the Blue Ridge Mountains after midnight.
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&& .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... The cold front will pass through the area from west to east Friday morning into the midday hours. The upper-level disturbance associated with the boundary will pass through our area during the afternoon and evening hours. Strong PVA ahead of this system along with mid-level frontogenetical forcing suggest that a period of rain will likely occur behind the front during the day Friday. Subsidence behind this system should allow for drying conditions to move in from west to east late Friday afternoon into Friday evening. Blustery northwest winds are expected behind the front Friday with falling temperatures. Confidence in the Max temp forecast is low for Friday due to uncertainty in the exact timing of the frontal passage. The upper-level disturbance will phase with northern stream energy and develop into an upper-level low Friday night. This will cause surface low pressure to rapidly intensify Friday night as it tracks off well to our north and east. The low will move up toward Nova Scotia Saturday into Saturday night while high pressure approaches from the west. A northwest flow between these systems will allow for dry and seasonably chilly conditions. A tight gradient between the departing low and building high will cause windy conditions during this time. The strongest winds are expected Saturday with gusts around 40 mph possible. Winds over the ridge tops may even be a bit higher Friday night and Saturday. An upslope flow will likely trigger a few showers for locations along and west of the Allegheny Front Friday night into Saturday morning. There will be enough cold air for a few snow showers. Snow may coat some grassy surfaces above 3kft. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... High pressure will build to our south Sunday and a westerly flow will cause more dry conditions along with sunshine. It will be breezy as well. A reinforcing cold front will approach Sunday night before passing through Monday. Little moisture will be associated with this boundary so most areas may end up dry. High pressure will return for Monday night through Wednesday...bringing dry and chilly conditions. && .AVIATION /14Z THURSDAY THROUGH MONDAY/...
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A boundary remains over the region early this morning. Warm air is overrunning this boundary and this has resulted in clouds...especially across the northern terminals. VFR conditions are expected this afternoon through this evening. A cold front will approach the terminals overnight before passing through Friday. Southerly winds and moisture ahead of the boundary may cause lower cigs overnight into Friday morning. Showers are also likely ahead of the front Friday morning and behind the front Friday afternoon. A wind shift is expected from the south to the northwest behind the boundary Friday morning....perhaps holding off until early Friday afternoon for the eastern terminals. Gusty northwest winds are expected behind the front later Friday through Saturday night. The strongest winds are expected Saturday with gusts around 30 to 35 knots possible. VFR conditions will continue for Sunday through Monday.
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&& .MARINE... A weak boundary over the waters this morning will retreat to the north as a warm front today. Southerly winds will increase behind the warm front this afternoon. A cold front will approach the waters tonight into Friday morning before passing through Friday around midday. Southerly winds will continue ahead of the front. A Small Craft Advisory is in effect for most of the waters later this afternoon through Friday morning. Did leave out the Upper Tidal Potomac for now thinking that the stronger wind field aloft may hold off until after peak mixing. Gusty northwest winds will develop behind the boundary Friday afternoon. A Small Craft Advisory is in effect for all of the waters. More gusty winds are expected Friday night through Saturday night. A Small Craft Advisory will be needed and a Gale Warning may be needed for portions of the waters during this time. High pressure will build to the south of the water Sunday before another cold front passes through Monday. High pressure will build in for the middle portion of next week. A Small Craft Advisory may be needed for portions of the waters during this time. && .TIDES/COASTAL FLOODING... The light onshore flow has led to elevated water levels. However...water levels are expected to remain below minor flood thresholds through this afternoon since the next high tide will be the lower of the two. Southerly winds will increase later this afternoon and continue through tonight. Tidal Anomalies are expected to increase during this time and this may cause minor flooding for sensitive areas during the high tide cycle tonight. Elevated water levels will continue into Friday morning before gusty northwest winds develop Friday afternoon. Blowout tides are possible Friday night through Saturday night due to a strong offshore flow. && .CLIMATE... Records for Wednesday were broken at Dulles and BWI airports. A record high minimum was set for Reagan National on Wednesday as well. See RER reports for details. Near record warmth is expected again today. Below is a list of record daily warm temperatures for October 20th. Record daily high temperatures Site 10/20 DCA 86 (1969) BWI 87 (1969) IAD 83 (1969) *also occurred in previous years Record daily warm low temperatures Site 10/20 DCA 64 (1885)* BWI 65 (1910) IAD 59 (1993) *also occurred in previous years && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory from 2 PM this afternoon to 6 PM EDT Friday for ANZ530>534-536>543. Small Craft Advisory from noon to 6 PM EDT Friday for ANZ535. && $$ SYNOPSIS...BJL NEAR TERM...BJL/HSK SHORT TERM...BJL LONG TERM...BJL AVIATION...BJL MARINE...BJL TIDES/COASTAL FLOODING...LWX CLIMATE...LWX is the U.S. government's official web portal to all federal, state and local government web resources and services.