Area Forecast Discussion
Issued by NWS Sterling, VA

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269 FXUS61 KLWX 160931 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 531 AM EDT Fri Mar 16 2018 .SYNOPSIS... Low pressure will linger over the Canadian Maritimes through Saturday. High pressure will build overhead today into tonight before weak low pressure passes through the area Saturday. High pressure will return for Sunday. Low pressure will impact the area late Monday into the middle portion of next week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Secondary surge of colder air is moving into the region this morning as upper level disturbance moves overhead. This will act to briefly induce some additional upslope snow showers along and near the Allegheny Front this morning, but accumulations will generally be less than one inch. In addition, some snow showers are being observed out ahead of the surge, and some of these will get into parts of western Maryland from Hagerstown to Frostburg and the panhandle of eastern West Virginia. A quick coating to half an inch of snow is possible, mainly on grassy surfaces. Elsewhere, some additional clouds or a few flurries will be possible in the early morning hours. Otherwise, a mostly sunny and once again blustery day is expected with wind gusts up into the 25-35 mph range, with the highest gusts across northern and central Maryland. With high pressure gradually building into the region, winds will be lighter further southwest towards parts of central/western VA and WV. Temperatures will be below normal, with highs in the 40s for most locations, except around 50F in central VA towards Charlottesville/Fredericksburg. With the wind, wind chills will not out of the 20s/30s for most locations.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY NIGHT/... High pressure will crest overhead tonight, leading to decreasing winds, dry conditions, and mostly clear skies. Some high clouds will begin to increase aloft ahead of the next approaching system, but they should be thin enough to not hinder radiational cooling all that much. Lows should bottom out between 20-30F. A fast moving low pressure system will then elongate and track from near St. Louis Saturday morning east-southeastward towards the NC/VA/TN region by late Saturday. Warm air advection and isentropic lift will lead to precipitation overspreading portions of the region Saturday morning, lasting into the afternoon, and ending by the evening. Given the cold start to the day and reservoir of cold air nearby across New England, at least some wintry precipitation is expected. The northern extent of the precipitation shield is still in question, as is the thermal profile evolution, but a stripe of accumulating snow is possible, in addition to some freezing rain/sleet Saturday morning, before changing to rain Saturday afternoon. At this time, the highest likelihood of seeing snow appears to be portions of the highlands in eastern West Virginia and western Maryland, with some light sleet/freezing rain accumulations possible west of the Blue Ridge. That being said, uncertainty remains. With the precipitation overhead through the day, highs will likely not get out of the upper 30s/low 40s for much of the region. If some areas don`t see precipitation, some mid 40s or even a bit higher are possible. Precipitation will taper off by Saturday evening as high pressure builds back overhead Saturday night. Lows Saturday night will fall back into the 20s to around 30F. Sunday should be a much nicer day, featuring mostly sunny skies and highs back up into the low to mid 50s. && .LONG TERM /MONDAY THROUGH THURSDAY/... Low pressure will likely track through the central CONUS Monday and toward the Appalachians Monday night before transferring its energy to a coastal low that will track up the Mid-Atlantic Coast Tuesday into Wednesday before tracking toward New England by Thursday. A confluent zone in the upper-levels of the atmosphere will continue to exist over New England between upper-level low pressure over the Canadian Maritimes and high pressure over the Great Lakes. This will build surface high pressure to our north over New England. This will likely put our area on the cold side of the storm with low pressure tracking through the Tennessee Valley Monday and transferring its energy to a coastal low off the Mid-Atlantic Coast Monday night into Tuesday. However, it is the middle of March so there is still a question as to how much cold air there will be for snow/wintry precipitation. Latest deterministic guidance shows the potential for rain or snow depending on subtle differences in the track of the low. Latest ensemble guidance shows a multitude of solutions as far as how strong the low will be and its exact track. Therefore, it is too early to pinpoint exact details. As of now it is increasingly likely that our area will be impacted by coastal low pressure Monday night into the middle portion of next week. There is even a possibility that the coastal low could hang around nearby for a few days due to the blocking pattern previously mentioned. Therefore...a prolonged period rain or snow cannot be ruled out. Will continue to monitor over the next several days as well as mentioning the possibility of wintry weather impacting our area during this time. && .AVIATION /10Z FRIDAY THROUGH TUESDAY/... VFR is expected through tonight with the main aviation weather concern another day of gusty northwest winds with gusts 20-30 knots. A period of light rain or mixed precipitation is likely Saturday and this may bring some sub-VFR conditions, with the highest likelihood at CHO. BWI/MTN have the lowest probabilities of impact. VFR then returns area-wide by Saturday night and continues through at least Sunday night. Low pressure will approach the Appalachians Monday before transferring its energy to a coastal low later Monday night and Tuesday. Rain or snow are likely Monday night and Tuesday with subVFR cigs/vsbys. && .MARINE... Small Craft Advisory conditions are expected across all waters through this evening with gusty northwest winds. As high pressure builds across the waters tonight, winds will diminish and drop below SCA criteria. Winds should then remain largely below criteria through Sunday night, although a brief period of marginal gusts may occur on Saturday across the northern Chesapeake Bay. Low pressure will approach the Appalachians Monday before transferring its energy to a coastal low later Monday night and Tuesday. Small Craft Advisories will likely be needed for the waters Monday night and Tuesday. && .FIRE WEATHER... More gusty winds are expected around low pressure over the Canadian Maritimes. Somewhat chillier conditions are expected as well with high temps in the 40s but fuels are drier compared to recent days. The relative humidity will drop to between 15 and 25 percent across central Virginia and 20 to 30 percent across northern Virginia, eastern West Virginia and Maryland. The strongest winds will be displaced from the lowest RH values (strongest winds over Maryland, northern Virginia and eastern West Virginia). An enhanced threat for the spread of wildfires is expected later this morning into early this evening given the fact that fuels will be dry and RH values will be low. Will issue a Special Weather Statement for areas where the winds are expected to be strongest (Maryland...eastern West Virginia and northern Virginia). Will leave central Virginia out for now since winds will not be as strong...but it will be quite dry. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory until midnight EDT tonight for ANZ530>543. && $$ SYNOPSIS...BJL NEAR TERM...MM SHORT TERM...MM LONG TERM...BJL AVIATION...BJL/MM MARINE...BJL/MM FIRE WEATHER... is the U.S. government's official web portal to all federal, state and local government web resources and services.