Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 120815 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 415 AM EDT Mon Mar 12 2018 .SYNOPSIS... Low pressure will pass to our south and weaken this morning. Low pressure will then redevelop off the Carolina coast later today and then rapidly intensify as it moves northeastward toward the Canadian Maritimes through Tuesday night. Canadian high pressure will build southward into the central U.S. and eventually the southeastern U.S. by Thursday. A weak cold front will push through the region Thursday night with Canadian high pressure building overhead for the first half of the weekend. && .NEAR TERM /THROUGH TONIGHT/... Regional radars show precipitation overspreading West Virginia, eastern Kentucky, and western Virginia early this morning associated with surface low pressure and mid level shortwave digging southeastward in to the mid south. This low will continue moving eastward this morning, passing south of our CWA, as it does it will weaken as a secondary area of low pressure forms off the Carolina coast later this morning. Precipitation is expected to finally reach our southwestern zones in VA/WV over the next few hours, bringing snow to these areas. Model guidance last evening and overnight has backed off quite a bit in terms of QPF and extent of precipitation coverage across our CWA. As a result, we have issued Winter Weather Advisories for portions of the central Shenandoah Valley, canceling the Winter Storm Warning. Generally, we are expected 1 to 3 inches of snow accumulation in the valleys with the potential for 2 to 5 inches along the ridges above 2000 feet. Snow covered roads are expected in these areas as snow increases this morning, bringing slippery and difficult travel conditions. Use caution if travelling through this region this morning. Elsewhere, snow amounts are expected to be much less, especially as you near the metro areas, where little to no accumulation appears most likely at this time. Best chance for accumulating snow fall will remain across central and southern Virginia. Check out our winter weather page at for the latest on forecast snow amounts. The coastal low pressure will take form later this morning and early afternoon off the Carolina coast, keeping the axis of heaviest precipitation south of our region. As this low pressure rapidly strengthens off the coast and moves northeastward, models do depict the chances for some snow developing on the backside of the system, mainly along and east of the I-95 corridor this evening, favoring northern and northeast MD. Not expecting much in the way of accumulation with this activity, potentially up to a half inch and residing mostly on grassy and elevated surfaces. As low pressure moves quickly northeastward toward New England overnight, winds will pick up out of the northwest and become gusty. Upslope snow showers will be ongoing along and west of the Allegheny Front, where minor accumulations will be possible. Temperatures will be seasonably cold tonight, falling to the 20s for most, with at or just below freezing in the cities. && .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... Mid to upper level troughing will remain over the northeastern U.S. through Wednesday night. We will see the tight pressure gradient continue across our area, bringing breezy conditions and colder than normal temperatures. Wind chills during the day will be in the 20s/30s and teens/20s at night, while single digits values are likely along our western ridgetops. Shortwave energy will move along the base of the aforementioned trough, promoting upslope snows over the favored locations and potentially snow showers east of the mountains. && .LONG TERM /THURSDAY THROUGH SUNDAY/... Reinforcing front comes through Thu for one last shot of cooler air. That high pressure area behind the front will settle over us Saturday morning and then slide offshore allowing for a moderation in temps. && .AVIATION /07Z MONDAY THROUGH FRIDAY/... Increasing moisture and cloud coverage expected this morning as low pressure passes to the south of the terminals. Latest guidance indicates the best chance for MVFR/IFR VIS/CIGs will be at CHO where the best chance for snow resides. Confidence is much less for terminals further north to experience sub-VFR conditions as the bulk of the moisture will remain to the south and east of IAD/DCA/BWI. As low pressure redevelops and strengthens off the Mid-Atlantic coast this evening, potential exists for snow to fall near BWI/MTN, resulting in sub VFR conditions. Confidence of this occurrence is too low to include in the forecast at this time. Conditions return to VFR at all terminals by Tuesday morning. Gusty northwest winds will prevail at the terminals through mid week as a strong pressure gradient will remain over the terminals. Upper level energy will swing overhead Tuesday and Wednesday, bringing the potential for brief periods of sub VFR conditions in passing snow showers, with the highest chances at MRB. && .MARINE... Winds have been on the increase early this morning as low pressure is approaching from the southwest. A Small Craft Advisory remains in effect for the lower Bay and Tidal Potomac early this morning, with all waters in the advisory today and through the day on Tuesday. Low pressure will develop and strengthen off the Carolina coast later today and moving northeastward through tonight. A strong pressure gradient will reside over the waters through Wednesday as low pressure churns near New England and Canadian high pressure slides southward in to the central and southeastern U.S. This will deliver gusty northwest winds during this time, with the potential for a short period of gale force gusts Tuesday afternoon/evening. Wind gusts will be near or above the small craft advisory criteria Wednesday into Thursday. Therefore, expecting advisories for most of this period. Winds should decrease into Friday below criteria but still breezy. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...Winter Weather Advisory until 2 PM EDT this afternoon for VAZ025-036-503-504-508. Winter Weather Advisory until noon EDT today for VAZ026-027- 029-037>039-507. WV...Winter Weather Advisory until noon EDT today for WVZ055-501- 502-505-506. MARINE...Small Craft Advisory until 6 PM EDT Tuesday for ANZ530>533-535- 536-538>542. Small Craft Advisory until 6 PM EDT Tuesday for ANZ534-537-543. && $$ SYNOPSIS...BKF NEAR TERM...BKF SHORT TERM...BKF LONG TERM...CS AVIATION...BKF MARINE...BKF is the U.S. government's official web portal to all federal, state and local government web resources and services.