Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 221512 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 1112 AM EDT Sat Apr 22 2017 .SYNOPSIS... A cold front is stalled to the south today. Low pressure will develop along the boundary...impacting our area through early next week. Low pressure will move out to sea Tuesday night and high pressure over the Atlantic will impact our weather for Wednesday. A cold front may impact the area late next week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... The frontal boundary that caused the showers/thunderstorms yesterday has shifted south of the area this morning with northerly flow in the low levels being observed across the region. At the same time, moisture/energy is streaming east- northeastward along the frontal zone out ahead of a closed low pressure system in the central Plains. Therefore a wet day is expected today, with the most widespread rain coming in two concentrated batches. First, widespread shower activity is currently spreading into the area from the southwest, and this will affect the region through the morning hours. It still appears there will be a bit of a lull in the early to mid afternoon hours, although scattered showers may still be around. Second more widespread period of rain, located over Kentucky and southern West Virginoa as of late this morning, will then move into our CWA as the afternoon wears on, lingering into the evening. Temperatures will follow a non-diurnal trend today with temperatures falling through the 50s. && .SHORT TERM /6 PM THIS EVENING THROUGH MONDAY NIGHT/... Periods of wet weather will continue across the Mid-Atlantic region into early next week. Some drier air is expected to nudge southward into the region tonight and into Sunday, and this will shift the focus for the rain southward across central and southern Virginia, with lower rain chances elsewhere. For some areas, especially DC north, later tonight and Sunday may actually end up being mainly dry, although will keep rain chances in the forecast as the northern extent of the gradient is uncertain, and the ECMWF is on the north end of the guidance envelope. Lows tonight in the 40s for most locations, with highs in the 50s under clouds on Sunday. More widespread rain will then push back northward for Sunday night through Monday night as low pressure system hits the east coast and slowly trudges northward. By Tuesday morning, the surface low center is still only progged to be near the Outer Banks of North Carolina. By 12z Tuesday, NAM/ECMWF/GFS suites all in relatively good agreement of a widespread long-duration rainfall ranging from about 0.5" north to possibly 2-3" south. Temperatures will be cool and relatively stable from Sunday night through Monday night with clouds and rain. Lows both nights in the 40s/50s, and highs in the 50s. && .LONG TERM /TUESDAY THROUGH FRIDAY/... Low pressure along the North Carolina coast Tuesday will slowly move out to sea Tuesday night. High pressure over New England will continue to wedge into the Mid-Atlantic during this time. Warm and moist air from the Atlantic Ocean will overrun cooler air near the surface...resulting in plenty of clouds along with rain Tuesday. Rain should dissipate in coverage as the low moves away from the area Tuesday night. The best chance for a soaking rain Tuesday into Tuesday evening will be across central and eastern portions of the CWA. The low will continue to move away from the area Wednesday and drier air should work its way into the area...allowing for some sunshine to return. A weakening cold front may impact the area Thursday. Bermuda high may control the weather pattern toward the end of next week with much warmer and more humid conditions. && .AVIATION /15Z SATURDAY THROUGH WEDNESDAY/... Low clouds and rain will affect the region through today with MVFR across the region this morning and persisting through the day. Steadier rain will result in periods of IFR. As drier air tries to work into the area tonight and Sunday, improvement to VFR is currently forecast for most sites, with the exception of CHO where the highest chances for continued widespread low ceilings and rain exist. Additional low stratus and rain will then overspread the region later Sunday and persist through at least Monday night, with sub-VFR conditions expected. Winds will be generally N-NE through the period. A soaking rain is likely Tuesday with subVFR conditions. Rain may taper off Tuesday night...but subVFR conditions will likely continue into Wednesday. Cigs/vsbys should gradually improve Wednesday as drier air works its way in behind departing low pressure. && .MARINE... North/northeast winds will intensify this morning with marginal SCA winds developing across the Chesapeake Bay and lower tidal Potomac. Periods of rain may limit mixing potential, but low level wind surge will likely be enough to reach 20 knots. Gusts will continue tonight as cooler air temperatures move over the warmer waters, leading to increased mixing. Marginal SCA again Sunday and Sunday night. SCA will then likely be needed Monday through Monday night as coastal low develops offshore and northeast winds intensify. Coastal low pressure will impact the waters Tuesday before slowly moving out to sea Tuesday night into Wednesday. A Small Craft Advisory will likely be needed for portions of the waters Tuesday through Tuesday night. Weak high pressure will build over the waters later Wednesday and a weakening cold front may impact the waters Thursday. && .TIDES/COASTAL FLOODING... A persistent onshore flow will develop behind a cold front through early next week. Elevated water levels are expected during this time...and minor flooding cannot be ruled out near times of high tide...especially Sunday into Tuesday. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory from 6 PM this evening to 6 AM EDT Sunday for ANZ539. Small Craft Advisory from 6 PM this evening to 6 PM EDT Sunday for ANZ531-540. Small Craft Advisory until 6 AM EDT Sunday for ANZ542. Small Craft Advisory from 6 PM this evening to 6 AM EDT Monday for ANZ543. Small Craft Advisory until 6 AM EDT Monday for ANZ532>534-537- 541. && $$ SYNOPSIS...BJL NEAR TERM...MM/RCM SHORT TERM...MM LONG TERM...BJL/MM AVIATION...BJL/MM/RCM MARINE...BJL/MM/RCM TIDES/COASTAL FLOODING...BJL

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