Area Forecast Discussion
Issued by NWS Sterling, VA

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
513 FXUS61 KLWX 220900 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 400 AM EST Wed Jan 22 2020 .SYNOPSIS... High pressure will move overhead today and gradually transition offshore by Friday. Low pressure will approach from the central United States on Friday night, then slowly move toward New England during the second half of the weekend. High pressure will return early next week. && .NEAR TERM /THROUGH TONIGHT/... Surface high pressure center is nearing the central Appalachians this morning while the mid and upper ridge axis is over the Mississippi Valley. Skies are clear to start, but some cirrus will be encroaching from the west as the day progresses, and especially into tonight. After starting in the teens and 20s this morning, daytime temperatures will moderate compared to the past two days due to the rising heights. Highs will range from the upper 30s to mid 40s. With the high remaining nearby through tonight, winds will remain light, thought cooling may be tempered a bit by the advancing clouds. Am still allowing some teens in the typically colder locations, with 20s elsewhere. && .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... Ridging will advance to the east on Thursday. Mid and high clouds will continue to advance ahead of a trough digging into the center of the country. High temperatures will be a bit warmer, with most locations will reach the 40s. Low pressure will be developing in the Mississippi Valley Thursday night. While a few ensemble solutions offer a faster solution, there is good consensus among deterministic models that the nighttime hours will remain dry in our CWA (and in fact probably well into the day Friday). Lows will be warmer but still below freezing in many locations. Moisture/lift associated with the low will spread into the area on Friday. There will be some dry air to overcome, so a slow onset makes sense. And most of the day could turn out dry along and east of roughly US 15. If precipitation begins quickly enough, there could be some spots below freezing west of the Blue Ridge, though am unsure if it would be valley locations, or on some of the ridges depending on how the column saturates to the wet bulb. It should be warm enough aloft for any such precipitation to be freezing rain versus snow. At this time, however, am expecting the bulk of the area to just see rain on Friday, with temperatures largely in the 40s by afternoon. As the closed upper low moves into the Ohio Valley Friday night, a new low is expected to develop along the trailing frontal zone, likely somewhere near Virginia. There will be a good surge of moisture and lift with this low, and at a minimum, a period of moderate to briefly heavy precipitation is expected. Rainfall totals could near an inch in some locations. What is uncertain is the thermal profiles during this time, and how quickly cold air will arrive on the back side of this system. Eventually, a changeover to snow will occur along the Allegheny Front. The question is whether the cold air can arrive east of there before precipitation begins to exit. Even so, were there to be snow Friday night, the chances should be confined along and west of the Blue Ridge, and most likely at the higher elevations. The event will turn more upslope in nature as the low pulls away, which is discussed further in the long term section. && .LONG TERM /SATURDAY THROUGH TUESDAY/... Mid to upper level trough and its cut-off low will be pushing ENE from the Midwest on Saturday. At the surface, occluded low pressure system will move from the Tennessee Valley into the Ohio Valley and Mid-Atlantic. Precipitation will be pushing from west to east on Saturday but conditions will be drying gradually through the day (except for the upslope areas). As this low pressure moves over our area and approaches the Mid-Atlantic coast, it will take a more NE track as it deepens. Lingering rain or snow showers possible into Saturday night. Greatest chance for any snow is at higher elevations, rain is expected elsewhere. Low pressure will continue to move away from us Sunday into Monday. NW flow and shortwave energy aloft could bring additional upslope showers through Monday. High pressure will build over our area Monday night into Wednesday. Temperatures during this period will be near or above normal for this time of the year with highs in the 40s and 50s (except at time over the ridges). Lows will be in the 20s and 30s. && .AVIATION /09Z WEDNESDAY THROUGH SUNDAY/... VFR conditions will continue through Thursday as high pressure moves across the area. Northwest winds this morning will become light and variable as the day progresses, eventually taking on an east or southeast component. Clouds will lower late Thursday night with MVFR ceilings and increasing rain chances Friday as low pressure approaches. IFR becomes more likely Friday night, along with a period of moderate rain, as the low moves overhead. Sub-VFR conditions on Saturday with a low pressure system impacting our region. Conditions should improve later Saturday as the system moves away. Winds will increase on Sunday with VFR conditions remaining into Monday. && .MARINE... North/northwest winds are finally starting to diminish on the waters as high pressure approaches from the west. By later today into Thursday, winds will become more northeasterly and should remain 10 kt or less. Winds will gradually increase Friday as low pressure approaches from the west, with Small Craft Advisory conditions becoming possible Friday night. Periods of SCA conditions possible Saturday into Monday with low pressure moving across our area Saturday. Winds will increase behind this system Sunday and remain it into Monday with SCA conditions possible during this time. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...ADS NEAR TERM...ADS SHORT TERM...ADS LONG TERM...IMR AVIATION...ADS/IMR MARINE...ADS/IMR is the U.S. government's official web portal to all federal, state and local government web resources and services.