Area Forecast Discussion
Issued by NWS Sterling, VA

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324 FXUS61 KLWX 180148 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 848 PM EST Sat Feb 17 2018 .SYNOPSIS... Low pressure will track northeastward along a stalled frontal boundary well to our south through tonight. High pressure will build in from the west on Sunday, migrating offshore by Monday. Low pressure will move northeastward toward the Great Lakes Monday, lifting a warm front northward through our region. A cold front is poised to approach the region during the middle portion of the work week. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
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Low pressure is beginning to develop off the Delmarva coast. However, regional radars suggest that the main area of precipitation moving onto the Eastern Shore. Rain had spread north to DC metro prior to its ending. So, believe that the accumulating snow has already fallen. With that in mind, have cancelled the Winter Weather Advisory for the Shenandoah Valley and the DC metro area. Am still watching precip tracking across Pennsylvania, which could affect northern Maryland. Also, only recently has the snow pulled away from metro Baltimore. Anticipate the rest of the Advisory will be able to be dropped before midnight. That turns the focus to the upslope potential. The best shortwave energy will be crossing in the 06-09 UTC window. That makes for a limited opportunity for additional accumulation... perhaps another inch or two. Considering reports to this point, warning criteria may not be reached. However, do not have the confidence to downgrade at this time. Temperatures will be hovering in the lower 30s for much of the night. Given snow and ice on the ground, slippery conditions may be an issue, and will strongly consider a Special Weather Statement to cover it. Am also concerned that the snow/ice on the ground will result in fog development since there will be little ventilating wind until dawn.
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&& .SHORT TERM /6 AM SUNDAY MORNING THROUGH MONDAY NIGHT/... High pressure quickly moves in behind the exiting low pressure area to the northeast, resulting in a dry and clear conditions. After a cold and perhaps icy start to the morning, temperatures will rebound nicely, topping out in the mid 40s to lower 50s region wide. High pressure shifts offshore Sunday night, keeping a light return flow over the region and temperatures above normal. Low pressure will move northeastward toward the Great Lakes region on Monday, which will help lift a warm front through our area. With warm air advection ongoing, could see some shower activity on Monday, not a complete washout, but definitely an increase in cloudiness. Highs Sunday/Monday will be above average, ranging in the low to mid 50s. Lows Sunday night will likely remain above freezing, and Monday night will remain in the upper 40s to near 50 degrees. && .LONG TERM /TUESDAY THROUGH SATURDAY/...
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High pressure will be offshore on Tuesday with return flow well settled over our region and an upper level ridge centered over the SE CONUS. Dry and above normal temperatures are expected Tuesday, with highs reaching the 70s for most of our CWA. A similar scenario is expected on Wednesday before a slow moving cold front approaches from the west. Guidance disagrees on the timing of the front, but there seems to be a consensus between some deterministic and ensembles that it will most likely move through later Wednesday or early Thursday. The front will stall nearby Thursday and into Friday which could keep the unsettled weather through the end of the week, with cooler -but still above normal- temperatures over our area. The front will lift as a warm front on Saturday, continuing the chances of rain over our area.
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&& .AVIATION /02Z SUNDAY THROUGH THURSDAY/...
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All precipitation has moved east of the terminals. However, low clouds linger. Am becoming concerned that without any ventilating wind, the clouds will remain and may be joined by developing fog. Pretty much have status quo (IFR) in the TAFs for a couple of hours past midnight. Will need to reassess what to do thereafter. VFR conditions will prevail Sunday and Sunday night. Light winds at 10 knots or less are expected. A warm front will lift north of the area on Monday, bringing a threat for shower activity and the potential for episodes of sub VFR conditions. VFR conditions expected Tuesday and part of the day Wednesday before sub-VFR periods possible late on Wednesday and into Thursday when unsettled weather could affect our area.
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&& .MARINE... With low pressure crossing the region through tonight, expect a weak gradient which will keep winds below criteria threshold. Winds will remain below advisory criteria through Monday as high pressure traverses our region and moves offshore, delivering light southerly winds over the waters. Winds are expected to remain below SCA criteria on Tuesday, even though they will be breezy. Similar conditions expected on Wednesday, therefore no small craft advisory expected these days. Winds will decrease on Thursday and remain below criteria. && .CLIMATE... A period of exceptional warm weather is expected Tuesday and Wednesday. Temperatures will be approaching if not exceeding record values. Below is a listing of record warm highs and record warm lows for this period. Record warm daily maximum temperatures SITE TUE 2/20 WED 2/21 DCA 76 (1930) 75 (1953) BWI 76 (1930) 74 (1930) IAD 70 (1971) 70 (1997) Record warm daily minimum temperatures SITE TUE 2/20 WED 2/21 DCA 59 (1939) 51 (1954) BWI 57 (1939) 49 (1981) IAD 46 (1981) 45 (1981) && .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...None. MD...Winter Weather Advisory until midnight EST tonight for MDZ003>006-011-014-501-502-505>508. VA...Winter Weather Advisory until midnight EST tonight for VAZ028- 503. WV...Winter Weather Advisory until midnight EST tonight for WVZ050>053-504-505. Winter Storm Warning until 2 AM EST Sunday for WVZ501-503. MARINE...None.
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&& $$ SYNOPSIS...BKF NEAR TERM...HTS SHORT TERM...BKF LONG TERM...IMR AVIATION...HTS/BKF/IMR MARINE...BKF/IMR CLIMATE...

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