Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 220846 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 346 AM EST Thu Feb 22 2018 .SYNOPSIS...
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A cold front will drop to our south today before stalling to our south tonight. The boundary will return north as a warm front Friday and it will stall out overhead Saturday. A stronger cold front will pass through from the west Sunday and high pressure will return for early next week. Saturday before a stronger cold front passes through from the west on Sunday. Low pressure may pass by to our south Monday before high pressure returns for the middle portion of next week.
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&& .NEAR TERM /THROUGH TONIGHT/...
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A cold front is passing through the area early this morning. The boundary will continue to push to our south later this morning through this afternoon. A wind shift to the north and eventually the northeast behind the boundary will allow for significantly chillier conditions compared to recent days. Temperatures will fall through the 50s early this morning and then through the 40s for most areas this afternoon. The front is shallow...meaning the low-level flow is expected to remain out of the southwest. This means that plenty of clouds will remain in place as warm and moist air overruns the cooler air near the surface. A few showers are possible early this morning as well...but more widespread light rain and drizzle is expected later this morning and afternoon as an upper-level disturbance passes through the area. The upper-level disturbance will move off to the east tonight...but an east to northeast flow on the cool side of the boundary will continue to usher in chillier conditions from the Atlantic. Warm and moist air will continue to overrun the surface cooler air resulting in plenty of clouds along with areas the likelihood of rain and drizzle. Rainfall amounts will be light. Min temps will range from the mid and upper 30s across most locations to perhaps the lower 40s in central Virginia. Will have to monitor locations near the Allegheny Front in western Maryland and eastern West Virginia. Temps may dip a close to freezing...causing the chance for light freezing rain/freezing drizzle. Higher resolution guidance continues to suggest this while lower resolution guidance keeps it warmer. Did lean the forecast closer to the higher resolution guidance and also noting the dewpoints in the 20s upstream over central PA. Have added the chance for freezing rain across these areas tonight and will mention in the HWO. Later shifts will have to take a closer look at the guidance and observations later today to determine if any headlines are needed.
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&& .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
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The boundary will return north as a warm front Friday into Friday night as low pressure tracks through the Great Lakes into Canada. Latest guidance has come into decent agreement showing that the boundary makes it into the Potomac Highlands and central Shenandoah Valley. This means that most areas will be on the cool side of the boundary with max temps in the 40s to perhaps lower 50s for most areas along with plenty of clouds and times of light rain and drizzle. However...some areas in the Potomac Highlands could punch into the warm sector later Friday with temps in the 60s possible. High pressure will swing across New England Saturday into Saturday night and this will likely keep the boundary hung up over our area for Saturday as well. With the boundary overhead...certainty in the forecast is low. The boundary will separate much cooler marine air from more very warm conditions for this time of year. Latest guidance shows the boundary most likely getting hung up just south and west of the Potomac River across the Potomac Highlands into central Virginia. Temps in the 40s and 50s are expected Saturday on the cool side of the boundary but temps in the 60s and perhaps 70s are expected on the warm side of the boundary. Shortwave energy will also pass through the area...bringing the chances for showers. The best chance for rain will be along and north of the boundary where isentropic lift will add to the forcing. The boundary will likely remain nearly stationary Saturday night. Showers are possible with min temps ranging from the 40s north and east of the boundary to the 50s and perhaps lower 60s south of the boundary.
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&& .LONG TERM /SUNDAY THROUGH WEDNESDAY/...
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Low pressure will track northeastward across the upper Great Lakes on Sunday while its associated cold front is poised to move through our region the second half of Sunday. This will result in elevated rain chances and the potential for a few thunderstorms with the frontal passage as guidance indicates some instability/CAPE. 850 temperatures will start the day Sunday in the 11-13C range with WAA ongoing and we reside in the warm sector ahead of the cold front. These factors will help to deliver highs in the upper 60s or perhaps in to the 70s should the warmer guidance win out. As the front slides through the area by Sunday evening, and modest CAA takes over, 850 temperatures will have dropped off a good 10C and nearing 0C across our western zones. GFS/ECMWF differ in the progression of the front, as the ECMWF stalls the front to our southeast on Monday, allowing a wave of low pressure to ride northeastward along it. This would keep chance POPs at least for the southern half of our CWA into Monday, while the GFS keeps the front much further south, thus our region remains dry. Will maintain rain chances during the day on Monday for now and see if a little better agreement can be achieved. High pressure of Pacific origin moves in from the west and sets up shop over our region through Tuesday. Temperatures during this period will continue to remain above normal with highs in the mid to upper 50s, and overnight lows above freezing in the 30s/40s. The aforementioned high pressure shifts off the Carolina coast on Wednesday, delivering a return flow across the region. Global models then diverge once again on the strength and timing of a low pressure area moving northeastward out of the ArkLaTex region. GFS is faster and stronger, bringing increased rain chances by Wednesday night, while the ECMWF is slower and weaker, keeping much of the precipitation away from our area. For now, have introduced chance POPs Wednesday night for much of the area. Regardless, clouds will be on the increase Wednesday and Wednesday night as an upper level jet resides overhead and undulations in the mid-levels near our region. Temperatures will remain above normal Wednesday and Wednesday night with WAA and cloud cover favored.
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&& .AVIATION /08Z THURSDAY THROUGH MONDAY/...
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A cold front will drop to the south today. Warm and moist air will overrun the surface cooler air in place...resulting in low clouds along with times of rain and drizzle through Friday night. IFR conditions are likely...but certainty as to when the IFR conditions begin is low. Will lean toward a majority of the guidance which shows IFR conditions moving in late this morning/early afternoon. Given the dry air advection and MVFR/VFR cigs upstream this does appear to suggest that MVFR cigs should hold on at least until mid-morning. The boundary may lift a bit farther north Saturday and Saturday night. Most terminals should still be on the cool side of the boundary which means more low clouds along with areas of fog...light rain and drizzle. Perhaps KCHO will have improving conditions with the boundary setting up just to their north. A cold front will approach and cross the area on Sunday, moving east of the terminals by Sunday evening. This will result in increased rain chances, and perhaps a few thunderstorms, as MVFR/IFR VIS/CIGs look like a good bet. Winds will favor a southerly trajectory ahead of the front, veering out of the west northwest Sunday evening while conditions gradually improve overnight Sunday as drier air filters in to the region. High pressure will move in from the west through Monday night, providing dry weather, light winds and VFR conditions at all terminals.
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&& .MARINE...
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A boundary will drop to the south today and northeast winds are expected through tonight. A pressure surge this morning and again later this afternoon and evening is expected. A Small Craft Advisory is in effect for all of the waters until 6 am and for the Maryland Chesapeake Bay and lower Tidal Potomac River today through this evening. There may be a lull in the wind gusts for a period late this morning into this afternoon in between pressure surges. The boundary will likely remain to the south through Saturday night. As of now...it appears that the gradient will be light enough for winds to remain below SCA criteria. SCA conditions possible Sunday as a cold front approaches from the west and crosses our waters by Sunday evening. This front will bring increased rain chances and perhaps a few thunderstorms with its passage. High pressure of Pacific origin will build in from the west in the wake of the FROPA, delivering light winds over our waters, with no headlines expected through Monday night.
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&& .CLIMATE...
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From Wednesday February 21st the following records were broken. For IAD: A monthly record high minimum temperature of 59 degrees occurred. This breaks the old record of 55 degrees set on February 17th 1976. The high of 80 degrees was also a monthly record, breaking the old record of 79 degrees set on February 24th 1985 and February 25th 2000. For DCA: A daily record high minimum temperature of 56 degrees occurred. This breaks the old record of 51 degrees set in 1954. The high of 82 degrees was also a daily record, breaking the old record of 75 degrees set in 1953. For BWI: A daily record high minimum temperature of 52 degrees occurred. This breaks the old record of 49 degrees set in 1981. The high of 79 degrees was also a daily record, breaking the old record of 74 degrees set in 1930.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory until midnight EST tonight for ANZ530>534- 537>543. Small Craft Advisory until 6 AM EST early this morning for ANZ535-536.
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&& $$ SYNOPSIS...BJL NEAR TERM...BJL SHORT TERM...BJL LONG TERM...BKF AVIATION...BJL/BKF MARINE...BJL/BKF CLIMATE...LWX

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