Area Forecast Discussion
Issued by NWS Sterling, VA

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910 FXUS61 KLWX 251428 AAA AFDLWX Area Forecast Discussion...UPDATED National Weather Service Baltimore MD/Washington DC 1028 AM EDT Wed Apr 25 2018 .SYNOPSIS... Low pressure will pass by just to east today and high pressure will return for tonight into Thursday. Low pressure will approach the area Thursday night before passing through the area Friday. A cold front will pass through Saturday and high pressure will return for early next week. && .NEAR TERM /THROUGH TONIGHT/...
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Low clouds remain stubborn this morning beneath an inversion. Given weak sfc flow, overcast skies will remain in place all day with cigs lifting slowly to 035-040 by day`s end. Isold-sct showers will remain possible through the day in weak sfc confluent flow this morning and then with passage of upper level trof. Previous afd... A northwest flow will gradually develop later this morning through this afternoon as the low passes by to our east. However, advection will be weak so drier conditions will be slow to take place. Having that been said...low clouds should gradually dissipate but a mostly cloudy to cloudy sky will remain in place this afternoon as the upper-level trough axis continues to swing through the area. Isolated to scattered showers are expected during this time, but it will not be a washout. Coverage may be a bit more widespread across southern Maryland and for locations near the Bay...closer to the surface low and upper-level low that is associated with the surface low. Max temps should top off in the 60s for most locations. The low will continue to move away from the area tonight and it will strengthen just a bit. This will cause the northwest flow to strengthen a bit and dry advection will be more pronounced. Therefore, any leftover showers should dissipate this evening and skies will clear out as well. Cool conditions are expected overnight with min temps in the 40s for most places north and west of Interstate 95 and lower to middle 50s south and east of I-95.
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&& .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... High pressure will build overhead for Thursday and it will remain dry and seasonable. High clouds may build later in the day ahead of the next area of low pressure. That low pressure is expected to approach the area Thursday night before passing through Friday. Guidance has come into better agreement with the details of this system, but some uncertainty does remain. As of now, it looks like this system will dip into some southern stream moisture and it will be strong enough to bring the likelihood for a period of rain overnight Thursday into Friday. The low will move off to the northeast later Friday, but the upper-level trough axis associated with the low will be passing through, so a few showers may persist Friday afternoon as well. Drier conditions are likely Friday night as any showers dissipate due to the loss of daytime heating and a westerly flow. && .LONG TERM /SATURDAY THROUGH TUESDAY/... An upper level disturbance will move from the eastern Great Lakes to the Northeast U.S. Saturday. An associated surface cold front will drag across our region Saturday and then to our southeast Saturday night. A moisture-starved cold front may only squeeze out a shower or two in parts of out region. Temperatures will be seasonable. High pressure will build in behind the cold front Sunday and linger through the middle of next week. Sunday`s highs could be 10 degrees cooler than Saturday`s high temperatures. Temperatures will modify on Monday, possibly reaching the upper 60s. Then, much of the region could encounter lower to middle 70s Tuesday with high pressure lingering over the mid-Atlantic. && .AVIATION /15Z WEDNESDAY THROUGH SUNDAY/...
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A very slow improvement to cigs/vsbys expected today with conditions becoming VFR by day`s end. High pressure will build over the terminals tonight through Thursday. There may be a period of northwest wind gusts around 15 to 20 knots tonight into Thursday ahead of the building high. Low pressure will approach the terminals Thursday night before passing through Friday. Rain and subVFR conditions are likely with the passage of this system. Drier conditions are expected Friday night, but patchy fog is possible. VFR conditions at all terminals Saturday through Sunday night. A brief period of MVFR cannot be ruled out in any passing showers on Saturday. Winds Saturday northwest 5 to 10 knots Saturday and Saturday night. Winds northwest 10 knots Sunday, diminishing Sunday night.
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&& .MARINE... Low pressure will pass by to the east today and the gradient will be relatively weak close to the low. Therefore, winds are expected to remain below SCA criteria. High pressure will build toward the waters tonight before settling overhead Thursday. A pressure surge will cause northwest winds to increase. A Small Craft Advisory is in effect for the Bay and lower Tidal Potomac River. The SCA may need to be expanded to include the upper and middle Potomac river as well, but confidence was too low at this time given the unfavorable timing of the pressure surge. For now, gusts have been capped around 15 knots across these areas. Low pressure will approach the waters Thursday night before passing through Friday. Winds may approach SCA criteria for portions of the waters, but confidence is low at this time due to uncertainly as to exactly how strong the low will be. Light winds are expected Friday night. No marine hazards expected Saturday through Sunday night. Winds northwest around 10 knots Saturday and Saturday night. Winds northwest 10 to 15 knots Sunday and Sunday night. && .TIDES/COASTAL FLOODING... Water levels running about a 1 to 1.5 feet above astronomical normals this morning. The winds over the waters have diminished, but anomalies should not change too much from where they are now through the morning tide cycle. Will continue with the Coastal Flood Advisory for St Marys County through the high tide cycle this morning. A northwest flow will develop later today but it will be light. This may cause anomalies to drop just a bit this afternoon, but confidence is low. If anomalies do not drop too much, then minor flooding for sensitive areas is possible. The northwest flow will strengthen tonight and this should cause anomalies to drop more significantly. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...Coastal Flood Advisory until 2 PM EDT this afternoon for MDZ017. VA...None. WV...None. MARINE...Small Craft Advisory from 9 PM this evening to 11 AM EDT Thursday for ANZ530>534-537>543. && $$ SYNOPSIS...BJL NEAR TERM...LFR SHORT TERM...BJL LONG TERM...KLW AVIATION...BJL/KLW MARINE...BJL/KLW TIDES/COASTAL FLOODING...BJL

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