Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 200814 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 314 AM EST Fri Jan 20 2017 .SYNOPSIS... A warm front will move into the area today and it will stall out overhead through Saturday. Low pressure will impact the area Sunday through Monday before finally moving away from the area Tuesday. A cold front will pass through the area Wednesday into Wednesday night and an upper-level trough may build overhead late next week. && .NEAR TERM /THROUGH TODAY/... Wave of warm air advection-driven rain will overspread the region from southwest to northeast over the course of the morning. Temperatures out ahead of the rain have fallen to near freezing in some locations, but they are expected to rise into the mid 30s to low 40s by onset time, so no ice is anticipated. Forcing associated with the rain bands will be weakening through the day as wave of low pressure moves northward into the lower Great Lakes and weakens, with warm air advection weakening as a result as well. Therefore rain amounts will be light, generally from one to two tenths of an inch. Rain will then taper off from west to east during the afternoon hours, with low clouds and drizzle possibly lingering after widespread rain ends. Temperatures will be above normal for late January, more mild south and west across the Shenandoah Valley and portions of eastern WV where rain ends earliest, coolest north and east across Maryland. Highs from the mid 40s to mid 50s. && .SHORT TERM /TONIGHT THROUGH SUNDAY NIGHT/... With little flow and lingering low level moisture, widespread low clouds and areas of fog and drizzle are expected overnight and into Saturday morning. As moisture thins, expecting improvement for areas west of the Blue Ridge by Saturday afternoon, with breaks of sun even possible. For locations east, solid overcast is more likely, although fog/drizzle should come to an end. Lows tonight around 40F under clouds/drizzle/fog, rebounding to the low to mid 50s for areas east of the Blue Ridge on Saturday, and low to mid 60s west. As large upper level low digs into the southern US Saturday into Sunday, deep south/southwest flow aloft develops along with low level easterly flow, establishing a moisture feed with the Gulf/Atlantic. This in combination with multiple waves of energy/moisture will lead to several rounds of rain moving across the region for the latter half of the weekend and into next week. && .LONG TERM /MONDAY THROUGH THURSDAY/... Cutoff surface low pressure in the southern branch of the jet will track northeast off the North Carolina coast before emerging off the Delmarva Coast Monday night. The low may stall out or remain nearly stationary off the Delmarva coast as it runs into blocking high pressure downstream...but the blocking high should dissipate Tuesday and the low will track off to our north and east during this time. A soaking rain is expected Monday through Monday night. Moisture from the Gulf of Mexico and Atlantic will overrun the surface cooler air in place...and strong forcing is expected with the low being close by. Latest GEFS indicates around 1-2 inches of rain possible during this time. The cutoff upper-level low associated with the surface low is expected to track overhead Monday through Monday night. This may cause enough dynamical cooling for rain to mix with or even change to a period of snow across the ridge tops of the Catoctin...Blue Ridge and Potomac Highlands. Details remain highly uncertain at this time but it does appear that the main ptype in the valleys will be rain. Drier conditions are expected Tuesday as the low moves away from the area...but a couple showers cannot be ruled out. A cold front will pass through the area late Wednesday into Wednesday night. Unusually mild conditions are expected ahead of the boundary. More seasonably chilly conditions are expected behind the boundary late next week. && .AVIATION /06Z FRIDAY THROUGH TUESDAY/... VFR conditions to start this morning will markedly deteriorate through the day as rain and low stratus overspread the region. Initially VFR/MVFR expected as rain overspreads the area, but will see widespread IFR/LIFR develop during the afternoon hours and persist into the evening. Areas of drizzle, fog, and low stratus will continue tonight and into Saturday with IFR/LIFR conditions expected. Some improvement expected Saturday afternoon, especially MRB/CHO. Additional Sub-VFR conditions expected Saturday night through at least Sunday night with additional periods of rain likely. IFR/Sub-IFR conditions are likely Monday through Monday night along with rain. Drier conditions are expected Tuesday as the low moves away from the area. Gusty northeast winds Monday will turn to the northwest later Monday night and Tuesday. && .MARINE... Sub-SCA conditions through Saturday night with southerly winds today, gradually turning southeasterly on Saturday. Winds increase markedly for Sunday and Sunday night out of the east/northeast with Small Craft Advisory conditions likely Sunday, with Gales possible Sunday night. Low pressure will move northeast toward the Delmarva Coast Monday night before slowly moving away from the area Tuesday. Gusty winds are likely with the low close by. A Small Craft Advisory will likely be needed Monday and Tuesday. A Gale Warning may be needed for portions of the waters Monday through Monday night. A cold front will pass through the waters later Wednesday into Wednesday night. && .TIDES/COASTAL FLOODING... Tidal Anomalies have decreased a bit due to the light winds. A southeast wind will develop today...but speeds will remain light. A light onshore flow will persist through early Sunday. Anomalies may not drop too much from where they are now...but they should remain low enough for water levels to remain below minor flooding thresholds. The onshore flow will strengthen later Sunday through Monday. Tidal flooding is possible during this time. The flow will turn offshore later Monday night and Tuesday. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...BJL NEAR TERM...MM SHORT TERM...MM LONG TERM...BJL AVIATION...BJL/MM MARINE...BJL/MM TIDES/COASTAL FLOODING...BJL is the U.S. government's official web portal to all federal, state and local government web resources and services.