Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 141015 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 615 AM EDT Wed Mar 14 2018 .SYNOPSIS... Low pressure will remain over the Canadian Maritimes through Friday while high pressure builds south and east from the central CONUS into our area. Weak low pressure will pass by to the south Saturday and high pressure will return for Sunday into Monday. Low pressure may impact the area during the middle portion of next week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Blustery and cold conditions expected for today with deep upper trough overhead and 850-mb temperatures dropping to near -10C. This will result in surface temperatures around 10F degrees below daily normals for mid-March, with highs ranging from the upper 30s to mid 40s. Most locations will start off the day with partly- mostly sunny skies, but instability clouds with the trough overhead will quickly fill in leading to a mostly cloudy afternoon. A few flurries are possible as well. In the northwest flow, upslope snow showers are ongoing near and along the Allegheny Front, and this will continue through the day. Most of the accumulating snow however will taper off this morning with a relative lull in the activity this afternoon, so will leave the advisory with an expiration time of 9 AM. With deep mixing expected, wind gusts are forecast to reach 25- 35 mph by later this afternoon on the back side of the upper trough. Thus, wind chills are likely to hold in the 20s/30s through the day. && .SHORT TERM /6 PM THIS EVENING THROUGH FRIDAY NIGHT/... Gusty northwest winds during the evening will lessen overnight, and mostly cloudy skies will trend clearer through the night. Cold air mass will remain in place, so lows expected to fall into the 20s to low 30s again. The next frontal system will be quickly approaching by Thursday morning as it rotates around the deep upper trough that will still be in place. Therefore, chances for upslope snow showers along and west of the Allegheny Front will be increasing towards sunrise. This system will cross the region during the day Thursday. While a mainly dry passage is expected, did increase chances for some rain/snow showers, mainly north/east of the DC metro during the day Thursday. In addition, upslope snow showers are expected, and another round of accumulating snow is likely. Temperatures will be a bit milder, with highs in the 40s/50s, but winds are expected to increase once again out of the west/northwest behind frontal passage by later in the afternoon. Quiet weather is then expected for Thursday night through much of Friday night as surface ridging builds overhead. Temperatures will still run below normals, with highs from the upper 30s to upper 40s, and lows in the 20s. Warm air advection will then be on the increase late Friday night into early Saturday morning, and some light precip will become possible across portions of western VA and eastern WV. && .LONG TERM /SATURDAY THROUGH TUESDAY/... Low pressure will track east from the central CONUS and it will pass by to the south Saturday. The low should weaken as it does so since it is running into a confluence zone between closed upper- level low pressure over the Canadian Maritimes and upper-level ridging over the north-central CONUS. A period of light precipitation is possible especially across southern areas. Light wintry precipitation cannot be completely ruled out if the precipitation can move in quick enough before temperatures rise well above freezing. Confidence in any wintry precipitation remains very low at this time. High pressure will build in from the north Saturday night through Sunday, bringing dry and seasonable conditions. Stronger low pressure may impact the area later Monday and Tuesday, bringing the next significant chance for precipitation. A blocking pattern with plenty of cold air to the north suggests that wintry precipitation is possible. Latest deterministic guidance has trended a bit weaker with the blocking high to our northeast, which would mean that the main p-type would be rain with the low tracking a bit farther north. However, confidence remains very low this far out especially with such a blocked pattern. Will continue to monitor over the next several days and for now, will continue with rain or snow possibilities in the forecast. && .AVIATION /10Z WEDNESDAY THROUGH SUNDAY/... VFR is expected through Friday night. Broken-overcast ceilings will develop each afternoon/evening in the 4000-7000 foot range, but remain VFR. A few flurries are possible this afternoon and some light rain showers are possible Thursday, but no significant reductions in visibilities are forecast. Gusty northwest winds are expected today with gusts to around 30 knots. These winds will lessen overnight, turn more southwesterly Thursday morning, before returning to the northwest Thursday afternoon with gusts around 25 knots. Northwest winds will persist into Friday as well. Weak low pressure will pass by to the south Saturday. Light precipitation is possible, especially across KCHO. High pressure will return for Sunday. && .MARINE... SCA conditions are ongoing in gusty northwest winds this morning. Winds are forecast to increase this afternoon, and a Gale Warning goes into effect at Noon today. Winds are expected to peak during the late afternoon and evening hours, before gradually abating overnight. A SCA continues overnight across portions of the waters. Another round of gusty winds is expected on Thursday, especially in the afternoon, and a SCA goes back into effect for all waters at Noon Thursday. These conditions likely persist through Friday. Weak low pressure will pass by to the south Saturday and high pressure will return for Sunday. Winds may approach SCA criteria during this time but it does appear marginal. && .FIRE WEATHER...
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Low pressure will remain over the Canadian Maritimes through Friday. High pressure will approach from the north and west during this time. A tight gradient between these systems will bring gusty winds to the area, especially from the late morning through the early evening hours each day. A downsloping west to northwest flow will cause low relative humidity. For today, frequent wind gusts around 25 to 35 mph along with relative humidity ranging from 15-25 percent across central Virginia and 25 to 35 percent across other locations may enhance the threat the spread of wildfires. Chilly conditions (temps in the 30s and 40s this afternoon) and higher fuel moistures will limit the threat somewhat. Therefore, no headlines have been issued. For Thursday, lower fuel moistures are expected along with gusty winds and low relative humidity. Temps will be in the 40s and 50s, a bit warmer compared to today. There will be an enhanced threat for the spread of wildfires, especially across central Virginia where winds will be strongest and relative humidity will be lowest (20-30 percent). For Friday...more gusty winds are expected. Somewhat chillier conditions may limit the RH drop a bit, but fuel moistures will be quite low.
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&& .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...Winter Weather Advisory until 9 AM EDT this morning for VAZ503. WV...Winter Weather Advisory until 9 AM EDT this morning for WVZ501- 503-505. MARINE...Small Craft Advisory until noon EDT today for ANZ530>543. Small Craft Advisory from midnight tonight to 6 PM EDT Thursday for ANZ530>534-537>543. Gale Warning from noon today to midnight EDT tonight for ANZ530>543. Small Craft Advisory from midnight tonight to 3 AM EDT Thursday for ANZ535-536. Small Craft Advisory from noon to 6 PM EDT Thursday for ANZ535- 536. && $$ SYNOPSIS...BJL NEAR TERM...MM SHORT TERM...MM LONG TERM...BJL AVIATION...BJL/MM MARINE...BJL/MM FIRE WEATHER...BJL is the U.S. government's official web portal to all federal, state and local government web resources and services.