Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 151953 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 253 PM EST Fri Feb 15 2019 .SYNOPSIS... A cold front will pass through the area this afternoon into this evening. Low pressure will track along the boundary, passing by to our south Saturday. High pressure will briefly build to our Saturday night and low pressure will pass through late Sunday into Sunday night. High pressure will build to our north early next week. Stronger low pressure may impact the area during the middle portion of next week. && .NEAR TERM /THROUGH SATURDAY/... A cold front will slowly move into the Potomac Highlands by late this afternoon and a southerly flow ahead of this system will allow for unusually warm conditions for this time of year. Max temps will be well into the 60s for most areas. The cold front will pass through the area this evening, and an isolated shower may accompany the frontal passage, but most of the time will be dry and any precipitation that does occur will be light. A northwest flow will develop behind the cold front, bringing a return of noticeably chillier conditions. Low pressure will track through the Gulf Coast States this evening and into North Carolina by Saturday morning. The low will pass by to our south Saturday morning into the midday hours before moving offshore later Saturday afternoon. The track of this system has shifted to the south, so that means that the most likely scenario is for northern and central areas to be dry, including Washington and Baltimore. However, a period of snow or rain/snow mix is expected across central Virginia and perhaps into southern Maryland late tonight through midday Saturday. Across these areas, any snow accumulation is most likely to be light and confined to grassy surfaces with temperatures near or above freezing for most of the time. However, accumulation snow is more likely in the mountains, especially across the central Blue Ridge Mountains near Interstate 64. A Winter Weather Advisory is in effect for this area for 1-2". Dry conditions will return across the entire area later Saturday afternoon, but it will be seasonably chilly with highs in the upper 30s to lower 40s for most locations. && .SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY NIGHT/... High pressure will briefly build toward the area from the north Saturday night, bringing dry and cold conditions. Low pressure is expected to track through the Ohio Valley Sunday before passing through our area Sunday evening. Warm advection ahead of the low will cause more clouds and the likelihood for light precipitation sometime later Sunday morning or afternoon, into Sunday evening. With very dry air in place to start, there will likely be enough of a cooling affect for in situ cold air damming. This means that a light wintry mix is possible, especially north and west of Interstate 95. Light snow or ice accumulations from snow/sleet and freezing rain are most likely across the climatologically favored areas (northern Maryland and near/west of the Blue Ridge and Catoctin Mountains). The low will move away from the area overnight Sunday and drier condtions should gradually return. Lows will be in the lower to middle 30s for most locations. && .LONG TERM /MONDAY THROUGH FRIDAY/... High pressure will build to our northwest on Monday. Northwesterly winds will advect cooler temperatures into the area. Other than a few upslope snow showers along the Allegheny Front, conditions are expected to stay dry. High temperatures will reach into the 40s following morning lows in the low 30s. High pressure will continue to build eastward to our north on Friday. Meanwhile, a positively tilted trough will dig southward across the Four Corners region. Downstream of the trough, the pattern will amplify a bit, with heights rising across south- central and southeastern portions of the country. As the trough ejects out from the Desert southwest, return flow will develop at low levels in response. With strong warm air advection occurring at lower levels, precipitation will break out across the southern US during the day Tuesday. This precipitation will progress off to the northeast along with the upper level trough, likely reaching our area Tuesday Night. With high pressure in place to our north, cold air may initially be locked in at low levels. As a result, some wintry precipitation may be possible. It`s far too early to focus in on exact timing and precipitation types, but with temperatures initially around freezing both at the surface and aloft, snow, sleet, freezing rain and rain are all within the realm of possibility. Chances for precipitation will extend into Wednesday as the weakening parent low tracks into the Ohio Valley and a weak coastal low forms off the Carolina Coast. Temperatures will warm aloft on Wednesday, but there is at least some potential for a wedge of cold air to remain locked in at the surface between the two areas of low pressure. As a result, some wintry precip can`t be ruled out during the day Wednesday, although snow appears less likely with temperatures warming aloft. Model guidance diverges by Thursday. The 12z GFS builds a weak area of high pressure in, allowing conditions to dry out, while the 00z Euro moves another wave of low pressure overhead, leading to continued chances for precipitation. High pressure should return late next week. && .AVIATION /19Z FRIDAY THROUGH WEDNESDAY/... VFR conditions are expected through this evening. Southwest winds will turn to the northwest behind a cold front. A period of snow or rain/snow mix is possible Saturday morning near KCHO, but other terminals should remain dry. VFR conditions are expected later Saturday through Sunday morning. Low pressure will pass by to the west later Sunday into Sunday night, bringing the likelihood for rain or a wintry mix. SubVFR conditions are possible during this time. VFR conditions are expected Monday and Tuesday. Conditions will likely deteriorate to sub-VFR Tuesday Night into Wednesday as a system approaches from the southwest. && .MARINE... A south to southwest flow will continue through late this afternoon ahead of a cold front. A Small Craft Advisory is in effect for all of the waters. The flow will turn to the north and northwest behind the cold front this evening and continue through Saturday. A Small Craft Advisory is in effect for the Bay and lower Tidal Potomac River tonight into Saturday morning. The SCA may need to be expanded into the upper Tidal Potomac River, but confidence was too low at this time due to a weak nocturnal inversion. High pressure will briefly build toward the waters later Saturday and Saturday night before low pressure passes by to the west later Sunday into Sunday night. The gradient should be weak enough for winds to remain below SCA criteria for most of this time. SCA conditions appear likely on Monday with gusty northwesterly flow in the wake of a departing area of low pressure. Winds will lighten Monday Night through Tuesday as high pressure builds to our north. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...Winter Weather Advisory from 4 AM to noon EST Saturday for VAZ508. WV...None. MARINE...Small Craft Advisory until 6 AM EST Saturday for ANZ530-531- 538-539. Small Craft Advisory until 10 AM EST Saturday for ANZ532>534- 537-540>543. Small Craft Advisory until 6 PM EST this evening for ANZ535- 536. && $$ SYNOPSIS...BJL NEAR TERM...BJL SHORT TERM...BJL LONG TERM...KJP AVIATION...BJL/KJP MARINE...BJL/KJP

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