Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 200018 CCA AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 818 PM EDT Mon Mar 19 2018 .SYNOPSIS...
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Low pressure over southern Missouri will push across the Tennessee Valley later tonight. A coastal low will develop along the mid- Atlantic Coast Tuesday ahead of this main low pressure system. A second low pressure system will develop off of the Tidewater of Virginia Tuesday night and move northeast Wednesday. Canadian high pressure returns for the latter half of the work week.
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&& .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... A large area of stratiform rain is pivoting across the Ohio Valley this evening. Expect this to move into the area after midnight for the western ridges, then progress eastward toward the metros by daybreak. Precipitation should start as all rain except over western Maryland and parts of the eastern West Virginia panhandle where it will be cold enough for a wintry mix of snow and sleet. An east-southeast flow at the surface will gradually back around to the northeast as energy from the western low transfers to the coast. Temperatures will be in the lower to middle 30s for the most part. Rain amounts will average one tenth to one quarter of an inch in northeastern zones and one quarter to one half inch in southwestern zones. Any ice accumulation will range from trace to a few hundredths of an inch and be mainly over the Appalachian Front, eastern West Virginia and western Maryland. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH WEDNESDAY NIGHT/... As the first storm, coastal low, develops nearshore Tidewater of Virginia, a transition from a wintry mix will become more of a snow and sleet mix Tuesday morning and continue through the remainder of day mainly west of the Blue Ridge. Significant snow and sleet accumulations are expected over the Potomac Highlands, with a glaze of ice expected as well across the Shenandoah Valley, Blue Ridge and northern Maryland. There should still be a lull in precipitation late Tuesday afternoon into Tuesday evening but with some uncertainties as to how long in time and coverage. Once the lull is over, an enhancement of precipitation will start up again sometime Tuesday afternoon and should be in the form of mainly snow. Some sleet may mix in at times. As it will be snowing in most areas to the north and west of the Metropolitan areas, a second coastal low will develop near the Delmarva Peninsula late Tuesday into Tuesday evening. As this low moves northeastward Tuesday night and early Wednesday, low pressure will reside at the surface and aloft over West Virginia, helping spread snowfall across much of the CWA. Overall we have increased precipitation amounts for our entire CWA through Wednesday. The models have trended toward a more wet and colder solution for the second of the two storms. The second low will pull away from the coast on Wednesday, bringing an end to precipitation by the evening. Temperatures through the period will remain below normal as cold air advection wins out along with precipitation and ample cloud cover affecting the region. && .LONG TERM /THURSDAY THROUGH MONDAY/... A high pressure system will be in control of our forecast area Thursday into Friday night allowing for dry conditions over most of our region. Northwesterly winds during these days could bring additional snow showers west of the Allegheny Front, mainly on Thursday. A boundary and low pressure system may affect us during the weekend bringing additional snow/rain to the area but there is still uncertainty on track and timing. && .AVIATION /00Z TUESDAY THROUGH SATURDAY/... MVFR/IFR VIS and CIGs expected to overtake the terminals toward daybreak as low pressure approaches from the west, bringing precipitation from south to north. A break in precipitation Tuesday afternoon could provide some improving conditions, but likely remain MVFR/IFR. Another low pressure area poised to bring wintry precipitation to the terminals Tuesday night and early Wednesday, resulting in continued MVFR/IFR VIS and CIGs. Winds are expected to be east southeast this afternoon, backing out of the north to northeast tonight, remaining at 10 knots or less. VFR conditions expected over the terminals on Thursday and Friday with high pressure in control. Breezy conditions expected on Thursday with gusts reaching up to 20 kts. Saturday conditions will depend on the track and timing of another low pressure system that could affect our area. && .MARINE... Low pressure will move south of our area tonight and redevelop off the coast early Tuesday. This will bring SCA conditions across our waters starting tonight. A Gale Warning has been issued for the lower Chesapeake as the low strengthens and passes to our east, delivering a strong pressure gradient over the waters. Small Craft Advisories to perhaps Gale Warnings are anticipated through the day Tuesday and will likely be required through the day on Wednesday as another low pressure area approaches the waters from the south. Wind gusts will be above small craft criteria on Thursday, therefore a small craft advisory is likely. Winds should remain below criteria Friday and Saturday. && .TIDES/COASTAL FLOODING... Two areas of low pressure will pass off the coast Tuesday and Wednesday, resulting in prolonged onshore flow. Water levels will be rising during this time, with minor flooding becoming possible by Wednesday. Exact projections are still uncertain at this time though. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...Winter Storm Watch from late Tuesday night through Wednesday evening for DCZ001. MD...Winter Weather Advisory from 6 AM to 6 PM EDT Tuesday for MDZ003>006-503-505-507-508. Winter Storm Watch from late Tuesday night through Wednesday evening for MDZ003>006-011-013-014-503>508. Winter Storm Warning from 5 AM to 8 PM EDT Tuesday for MDZ501- 502. Winter Storm Watch from Tuesday evening through Wednesday afternoon for MDZ501-502. Winter Storm Watch from Wednesday morning through Wednesday evening for MDZ016>018. VA...Winter Weather Advisory from 6 AM to 6 PM EDT Tuesday for VAZ025>031-503>505-507-508. Winter Storm Watch from late Tuesday night through Wednesday evening for VAZ025>031-040-052>054-501-503>508. WV...Winter Weather Advisory from 6 AM to 6 PM EDT Tuesday for WVZ051>053-505-506. Winter Storm Watch from late Tuesday night through Wednesday evening for WVZ051>053. Winter Storm Warning from 5 AM to 8 PM EDT Tuesday for WVZ050- 055-501>504. Winter Storm Watch from Tuesday evening through Wednesday afternoon for WVZ050-055-501>506. MARINE...Small Craft Advisory from midnight tonight to 6 PM EDT Wednesday for ANZ531>533-537-539>542. Small Craft Advisory from 6 AM Tuesday to 6 PM EDT Wednesday for ANZ530-535-536-538. Small Craft Advisory from midnight tonight to 6 AM EDT Tuesday for ANZ543. Small Craft Advisory from 6 PM Tuesday to 6 PM EDT Wednesday for ANZ534-543. Gale Warning from 6 AM to 6 PM EDT Tuesday for ANZ534-543. Small Craft Advisory until 6 AM EDT Tuesday for ANZ534. && $$ SYNOPSIS...KLW NEAR TERM...KLW/DHOF SHORT TERM...KLW/DHOF LONG TERM...IMR AVIATION...IMR/KLW/DHOF MARINE...IMR/KLW/DHOF TIDES/COASTAL FLOODING...KLW is the U.S. government's official web portal to all federal, state and local government web resources and services.