Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 180129 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 929 PM EDT Mon Oct 17 2016 .SYNOPSIS... High pressure in the western Atlantic will remain in place for the next several days. A cold front will slide southward into the area Wednesday before lifting back north Thursday. Another, stronger cold front will cross the region Friday. High pressure will return for the weekend. && .NEAR TERM /THROUGH TUESDAY/... High pressure has settled south and east of the area and will move little through Tuesday. Meanwhile, heights aloft rise as ridge expands into the southeastern states. Light south to southwest winds are bringing warmer and more humid air northward. The increased moisture combined with the longer October nights, however, will mean more fog is possible later tonight into early Tuesday morning. Several locations are already near their dew points. There is a patch of mid level clouds across northeastern parts of the CWA, but as these exit, only thin high clouds are expected. So the most prominent limiting factor on the fog will be a light breeze since the high is not directly overhead. Otherwise, tonight will be mild with lows in the 50s and 60s. A few minor adjustments may be required to the forecast based on latest obs. Winds will be more noticeable on the ridgetops tonight thanks a low level jet around Great Lakes low pressure. Gustier conditions will reach low elevations by late morning, although generally less than 20 MPH. The good mixing will promote well above normal temperatures, if not summerlike due to dew points in the 60s. Mid 80s are likely and records could be threatened. See the climate section below for potential records which may be reached or broken. && .SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/... High pressure to the southeast will weaken a bit Tuesday night into Wednesday as a cold front presses southeastward from Canada. Guidance suggests that this front will become parallel to the southwesterly upper level flow and end up stalling out in our vicinity Wednesday night, then lift back north Thursday as winds aloft shift more southerly ahead of the approaching deep trough. The result would be another warm day Wednesday, but a chance of showers as the front slides south into the area later in the day and at night. Some cooler air could reach the metro Wednesday night, but odds favor the front lifting back north Thursday with more warm weather. The approaching front to the west may start to bring more showers of its own later Thursday, so that potential must be watched. Again, see climate section below for potential records during this period. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... Guidance offers differing solutions with cold frontal passage towards the end of the workweek. ECMWF has frontal passage late Thursday into Friday with a flatter trough axis...while GFS (and most of its ensembles) depict a frontal passage Friday afternoon/night with a deeper trough axis. Have leaned more on ECMWF solution, as it has exhibited the most run-to-run consistency. Thus, currently expect greatest precip chances overnight Thursday into Friday...with cooling temperatures Friday into the weekend as high pressure builds into the region. While temperatures this weekend will be cooler than during the week, they really only fall to a few degrees below climatology...with L/M60s expected for highs. By Sunday/Monday low temperatures will be in the 40s in most locations. && .AVIATION /01Z TUESDAY THROUGH SATURDAY/... VFR during the day/evening through the next few days as high pressure remains dominant. Main fly in the ointment will the the repetitive threat of fog each morning, mainly IAD/MRB/CHO, but also possibly BWI. With 00Z issuance, have introduced IFR at CHO due to LAMP guidance and MVFR at MRB due to climo/persistence. However, IFR or lower could occur at any of IAD/MRB/CHO, with the main limiting factor being a light wind. Will have to monitor for MVFR or lower vsby Wednesday morning as well. Otherwise, mainly S to SW winds 5-10 knots (a gust to 20 kt possible Tuesday afternoon) expected with no precip. Showers will become possible later Wednesday into Thursday as a front slips southward. Significant precip with IFR cig/vis reductions are not expected with this feature; some MVFR cig/vis is not impossible, though. A cold front will pass through the area late Thursday night into Friday...bringing the chance for showers and sub-VFR conditions. VFR conditions should prevail Saturday as high pressure begins to build back into the area. && .MARINE... Southwesterly flow will predominate through the next few days as high pressure remains to the southeast. With southerly channeling looking unlikely tonight, think winds stay below SCA thresholds. Mixing does look fairly sufficient on Tuesday, and could see some 20 kt gusts. However, given threshold nature in forecast soundings, will allow one more model cycle before hoisting an advisory. Winds should be lighter on Wednesday. Southerly flow will continue over the waters Thursday in advance of approaching cold front. Cold front is expected to pass through the waters Friday...with small craft conditions likely along/behind the front Friday into Saturday. Some guidance even suggests gales. && .TIDES/COASTAL FLOODING... A southwest flow will continue over the waters through Wednesday. Elevated water levels are expected during this time. Some thresholds will continue to be threatened...but only by an inch or so at times. The anomaly has rebounded enough at DC SW Waterfront to issue a Coastal Flood Advisory for the evening high tide cycle. Elevated water levels will likely continue into Friday before an offshore flow develops behind a cold front. && .CLIMATE... Below is a list of record daily warm temperatures for October 17th through 20th. Washington-Dulles broke the record high temperature today, October 17th. Record daily high temperatures Site 10/17 10/18 10/19 10/20 DCA 86 (1938)* 85 (1938)* 88 (1938) 86 (1969) BWI 90 (1938) 82 (1945)* 82 (1947)* 87 (1969) IAD 83 (1963) 82 (2007)* 83 (1991)* 83 (1969) *also occurred in previous years Record daily warm low temperatures Site 10/18 10/19 10/20 DCA 68 (1947)* 65 (1905) 64 (1885)* BWI 69 (1928) 67 (1905) 65 (1910) IAD 60 (1968) 60 (2011) 59 (1993) *also occurred in previous years && .LWX WATCHES/WARNINGS/ADVISORIES... DC...Coastal Flood Advisory until midnight EDT tonight for DCZ001. MD...None. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...RCM NEAR TERM...ADS/RCM SHORT TERM...RCM LONG TERM...MSE AVIATION...ADS/MSE/RCM MARINE...ADS/MSE/RCM TIDES/COASTAL FLOODING...ADS/RCM CLIMATE...DFH is the U.S. government's official web portal to all federal, state and local government web resources and services.