Area Forecast Discussion
Issued by NWS Sterling, VA

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209 FXUS61 KLWX 210920 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 420 AM EST Mon Jan 21 2019 .SYNOPSIS... Arctic high pressure will build over the region through Tuesday, before sliding off the Mid Atlantic coast Tuesday night. A cold front will move into the Ohio Valley on Wednesday, as low pressure riding along the boundary moves across the area Wednesday night and into Thursday. Another cold front will cross the area on Friday as high pressure builds back over the region the first half of the weekend. && .NEAR TERM /THROUGH TONIGHT/... Arctic high pressure stretches from Ontario southward into the Mississippi River Valley this morning, as low pressure over Nova Scotia continues its track northward. The strong pressure gradient between the building high and exiting low continues to produce strong northwesterly winds across the Mid Atlantic, with gusts of 25-35 mph being observed over the CWA. The main story this morning, and really through tonight will be the very cold temperatures being driven into the region. Observations early this morning have temperatures in the single digits to teens across the area. Factor in the winds mentioned above, wind chill values are below zero for a majority of locations, with some dangerously cold values as low as -25 to -30F along the higher elevations of the Alleghenies. As such the Wind Chill Warning remains in effect until this afternoon for the higher elevations of the Alleghenies, and a Wind Chill Advisory continues for everyone else through 11am. Given the gradient remains strong with the exiting low and building high, wind chills will hover around zero for much of the day as highs likely hold in the teens, with low 20s along our far southern zones. Did consider a potential Wind Advisory this morning into early afternoon for portions of northern and northeast MD, as we could see some gusts upwards of 40-45mph. Don`t think the frequency of Advisory level gusts and the overall likelihood is high enough at this time to warrant an issuance. Regardless, a blustery and very cold day is in store for the region, despite ample sunshine. Be sure to dress in layers if you are planning on spending anytime outdoors today, ensuring to protect any exposed skin. High pressure will build overhead tonight, with clear skies and a gradual decrease in winds. This will allow wind chills to remain below Advisory levels, however low temperatures will be exceptionally cold in the single digits for much of the area, teens being observed in the cities and near the larger bodies of water. Locations along the Alleghenies, Potomac Highlands, as well as portions of the Shenandoah Valley will likely fall below zero. && .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... The high will begin to shift off the coast Tuesday afternoon and Tuesday night as a return flow sets up over the area. Temperatures will rebound on Tuesday back into the 30s under mostly sunny skies, but remain below normal for the latter half of January. Clouds will be on the increase Tuesday night as southwest flow aloft and warm air advection improves ahead of a frontal boundary cross the Mississippi Valley and low pressure nears the Great Lakes. As clouds increase Tuesday night ahead of the approaching system, some light wintry precipitation will be possible across portions of western MD/WV in the predawn hours Wednesday. Not expected much in the way of accumulation, but some light freezing rain and/or sleet will be possible. Low temperatures Tuesday night will range from the lower 20s to near 30 degrees. The frontal boundary will near the area on Wednesday, bringing rain to the region as warmer air wins out with highs in the middle 40s to lower 50s. The boundary will linger across the area Wednesday night as low pressure moves along it. This will result in periods of moderate to heavy rainfall. As the low nears the Delmarva late Wednesday night and early Thursday morning, colder air will try to filter in on the backside to bring a change over to rain/snow in the Alleghenies. && .LONG TERM /THURSDAY THROUGH SUNDAY/... A low pressure system will move across our region Thursday. Rain, associated with the low, will be moderate to heavy at times with the potential for a little snow on the back side of this low. Once the low moves off the East Coast, drier air will encompass much of the region with the possibility of some upslope snow showers in the Potomac Highlands Thursday night. Colder temperatures and drier air will ensue Friday and Friday night before a brief cold front makes an attempt to cross the region late Saturday into Saturday night. A couple of snow showers or squalls could develop with this front. An arctic high will build in behind this front and settle overhead, briefly, late Saturday night into early Sunday. Another low pressure system will develop to our south Sunday into Monday and move northeast either over the Interior Southeast U.S. or near the East Coast. Either way, this storm should be the one to watch throughout the week as it has the potential to pull in colder air from the northwest and enable the development of some accumulating snowfall. The European model is hinting of this very thing. However; timing and intensity of this storm system is how the GFS model is differing from the European. && .AVIATION /08Z MONDAY THROUGH FRIDAY/... Gusty northwest winds and VFR conditions will persist today across the terminals. As high pressure builds over the terminals tonight, winds will abate, with clear skies and VFR conditions persisting through Tuesday night. A return to sub VFR conditions likely on Wednesday as a frontal boundary and low pressure crosses the terminals through Wednesday night with rain, at times heavy, expected. IFR conditions possible Thursday with rain overspreading the region. Conditions should improve to MVFR or VFR Thursday night as the low pressure pulls away. Winds southwest shifting northwest 10 to 15 knots Thursday, diminishing Thursday night. VFR conditions Friday and Friday night. Winds west around 10 knots becoming northwest 10 to 15 knots Friday night. && .MARINE... Gale Warnings remain in effect through this afternoon for all waters. Small Craft Advisory conditions will linger tonight before winds subside late as high pressure builds over the waters. With the high overhead, then shifting off the coast late Tuesday, sub SCA conditions expected through this time. Winds will increase late Tuesday night, and especially Wednesday/Wednesday night as southerly flow increases and low pressure nears the waters, with SCA conditions likely. Small craft advisories likely Thursday. Winds southwest shifting northwest 15 knots gusting to 25 knots. Small craft advisories possible Thursday night through Friday night. Winds northwest becoming west 10 to 15 knots with possible higher gusts. && .TIDES/COASTAL FLOODING... Persistent and strong northwest flow will yield blowout conditions through tonight. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...Wind Chill Advisory until 11 AM EST this morning for DCZ001. MD...Wind Chill Warning until 1 PM EST this afternoon for MDZ501. Wind Chill Advisory until 11 AM EST this morning for MDZ003>006-011-013-014-016>018-502>508. VA...Wind Chill Warning until 1 PM EST this afternoon for VAZ503- 504. Wind Chill Advisory until 11 AM EST this morning for VAZ025>031-036>040-050>057-501-502-505>508. WV...Wind Chill Warning until 1 PM EST this afternoon for WVZ501- 503-505-506. Wind Chill Advisory until 11 AM EST this morning for WVZ050>053-055-502-504. MARINE...Small Craft Advisory from 4 PM this afternoon to 6 AM EST Tuesday for ANZ530>543. Gale Warning until 4 PM EST this afternoon for ANZ530>543. && $$ SYNOPSIS...BKF NEAR TERM...BKF SHORT TERM...BKF LONG TERM...KLW AVIATION...BKF/KLW MARINE...BKF/KLW TIDES/COASTAL FLOODING...BKF

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