Area Forecast Discussion
Issued by NWS Sterling, VA

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382 FXUS61 KLWX 121944 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 244 PM EST Mon Feb 12 2018 .SYNOPSIS... High pressure will build north of the area tonight through Tuesday before pushing offshore Tuesday night. A warm front will then cross the region during midweek, followed by a cold front late in the week. && .NEAR TERM /THROUGH TONIGHT/... A few lingering rain showers remain across portions of southern Maryland and central Virginia early this afternoon, but these too will push eastward and out of the region by late in the day as the upper level energy and shortwave trough pull away. Low level clouds have been decreasing through the day and this trend will continue with variable amounts of mid/high clouds remaining, more south/east, less north/west. Strong high pressure (1045mb) will then build to our north through the night and into Tuesday morning, leading to significant drying and skies becoming mostly clear. Some high clouds will continue to move across the region in the west/southwest flow aloft but they should be pretty thin. Northerly flow will persist through the night, but winds should gradually lessen. Thus, temperatures should be able to drop into the 20s for much of the region, except around 30F in the urban centers and some teens in the coldest locations. && .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... Surface high pressure will move eastward across upstate NY and New England, moving offshore of southern New England by the evening. A ridge axis will also wedge itself southward across our area down into the Carolinas, as is typical of cold air damming scenarios. At the same time, warm air advection will begin aloft atop the cooler low levels, which will lead to mostly sunny skies to start the day seeing an increase in clouds from the south/west during the day. Some light precipitation is also possible (<20%) across portions of the lower Shenandoah Valley, central Blue Ridge, and Highland County VA during the day Tuesday, and coverage will be spotty at most, however it is possible for some light freezing rain with temperatures near or below freezing for the first half of Tuesday. By later in the afternoon, high temperatures will reach into the upper 30s to mid 40s. Warm air advection will continue Tuesday night, and that combined with added cloud cover will keep temperatures mainly in the 28-35F range. Some light precipitation becomes possible along and west of the Allegheny Front late Tuesday night and Wednesday morning. Temperatures will be rising, but if precipitation does arrive early enough, there is a low potential again for a bit of very light freezing rain (<25%). Moisture and warm air advection will also act to increase shower chances through the day, although mainly west of the Blue Ridge Mountains. High temperatures Wednesday should be able to rise through the 50s. A more organized area of rain then becomes increasingly likely Wednesday evening and Wednesday night as a weak system passes north and a warm frontal zone crosses the region. No mixed precipitation issues are expected with lows Wednesday night in the 40s to around 50F. && .LONG TERM /THURSDAY THROUGH MONDAY/... One shortwave scoots off to the east Thursday morning which should leave most of the day dry. Mild temperatures will continue, especially if we can develop breaks in the clouds given deep SW flow and an anomalously strong (590 dm 500 hPa) ridge centered over Florida. Another wave of rain looks to accompany a cold frontal passage Friday, though with more of a westerly component to the wind amounts may tend to be on the lighter side. A much cooler (seasonable) airmass will take over for the weekend. A weak wave of low pressure will likely develop along the aforementioned front to our south Saturday. One GEFS member and two Canadian ensemble members/operational GGEM (from 00z runs last night) are a little more amplified and bring precipitation into the area, but this looks like a very low probability solution at the present time. Strong building high and NW flow should push any area of low pressure to the south of the area. Temperatures should gradually moderate by early next week as high pressure moves offshore. && .AVIATION /19Z MONDAY THROUGH SATURDAY/... VFR is expected through at least Tuesday evening. Northerly winds around 10-12 knots with gusts up to 20 knots are expected this afternoon under gradually clearing skies. Winds diminish tonight and stay light on Tuesday with VFR continuing. There is potential for some lower ceilings at times Tuesday night and Wednesday with warm moist air returning, but chances are low (<30%) at this time. Higher probabilities exist for some MVFR ceilings Wednesday night with areas of showers. Mainly VFR Thu-Sat. Some MVFR possible in -RA first thing Thu AM and again Fri PM. Winds generally SW around 10 kts. && .MARINE... SCA remains in effect for all waters through the rest of today as cold air pushes back into the region behind a cold front. Winds have lessened this afternoon, but still seeing scattered gusts into the 18-23 knot range. Most locations then drop below SCA criteria this evening and remain that way through tonight. However, as high pressure does build in and flow becomes more northerly, channeling is likely to lead to another surge of winds up to about 20 knots tonight into early Tuesday morning. Thus, have extended the SCA for portions of the central Chesapeake Bay and lower Tidal Potomac. Sub-SCA winds return for much of Tuesday through Wednesday. Winds may then reach SCA criteria as southwest flow increases Wednesday night. Despite poor mixing over cooler water on SW flow, the gradient should be strong enough to result in SCA gusts on at least portions of the waters Thursday into Thursday night. SCA gusts are more likely in NW flow behind a cold front Friday into Saturday. Winds should go light by Saturday night as high pressure moves overhead, then remain light through the remainder of the weekend. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory until 6 PM EST this evening for ANZ530>532-535-536-538>542. Small Craft Advisory until 9 AM EST Tuesday for ANZ533-534-537- 543. && $$ SYNOPSIS...MM NEAR TERM...MM SHORT TERM...MM LONG TERM...DHOF AVIATION...MM/DHOF MARINE...MM/DHOF

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