Area Forecast Discussion
Issued by NWS Sterling, VA

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792 FXUS61 KLWX 172005 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 305 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 /THROUGH TONIGHT/... Precipitation has moved in across the area this afternoon, starting as a snow/sleet mix along and north of the I-66 corridor, while some light rain started the festivities a little further to the south. We are seeing a light mix of rain and snow at DCA and BWI as temperatures hover near 40 degrees, but as the column cools, do expect a transition to a snow/sleet mix. Mainly snow is expected across the northern third of our CWA, but some sleet mixing cannot be ruled out. One change to our winter weather headlines was to include the remainder of Baltimore county and the City of Baltimore in the Advisory, as we could see 1 to 2 inches in those areas. Precipitation will increase in intensity throughout this afternoon and into this evening as favorable lift moves closer to our region. The added lift is owing to the approach of a potent shortwave and the proximity of the right entrance region of the upper level jet moving overhead. By this evening, low pressure off the MD/VA coast will also be developing in the baroclinic zone residing along the coast. This low pressure area will quickly move northeastward away from our region, dragging with it much of the heavy precipitation off to our east as well. The snow/sleet will have a hard time sticking to pavement with the preceding warmth we`ve experienced, but if precipitation comes down hard enough, these surfaces could quickly cool and obtain a bit of slushiness, especially if untreated. Do expect precipitation to come to an end for the entire area by midnight, but likely a couple hours sooner especially the further southwest you venture in our CWA. Overall, storm total accumulations along the northern tier of the CWA are expected to be between 2 to 5 inches, with 1 to 3 inches along and west of the Blue Ridge. The immediate D.C. metro will likely see mostly a wintry mix, perhaps even some rain this evening, which will keep totals at an inch or less, mostly on grassy and elevated surfaces. Once again the highest amounts will be found along and west of the Alleghenies, where western Grant/Mineral are expected to receive upwards of 5 to 7 inches. Please visit our winter weather page at weather.gov/lwx/winter for a myriad of snowfall projections for this event. Do have some concerns for icy spots overnight and early Sunday morning as temperatures will fall to near freezing in the metro areas, and below freezing to the north and west. If travelling overnight and into early Sunday morning, use caution, especially on untreated roadways and surfaces. && .SHORT TERM /SUNDAY 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 FRIDAY/... 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. && .AVIATION /20Z SATURDAY THROUGH THURSDAY/... IFR and possibly LIFR CIGS/VIS at times this afternoon and into tonight as wintry precipitation moves across the area from the southwest. Periods of heavy snow/sleet are possible as precipitation intensity maximizes late this afternoon and early evening. The system quickly exits the terminals by 04z, resulting in a return to VFR conditions, which will prevail through 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. && .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... DC...None. MD...Winter Weather Advisory until midnight EST tonight for MDZ003>006-011-501>503-505-507-508. VA...Winter Weather Advisory until midnight EST tonight for VAZ025>031-040-501-503>505-507-508. WV...Winter Weather Advisory until midnight EST tonight for WVZ050>053-055-502-504>506. Winter Storm Warning until 2 AM EST Sunday for WVZ501-503. MARINE...None. && $$ SYNOPSIS...BKF NEAR TERM...BKF SHORT TERM...BKF LONG TERM...IMR AVIATION...IMR/BKF MARINE...IMR/BKF CLIMATE...RCM

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