Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 190902 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 402 AM EST Fri Jan 19 2018 .SYNOPSIS... High pressure to the south will dominate the weather through the weekend. A storm system and cold front will cross the region late Monday and early Tuesday. High pressure will return by the middle of next week. && .NEAR TERM /THROUGH TONIGHT/... Surface high pressure is located near the central Gulf Coast this morning while the tail end of a northern stream shortwave trough is crossing the area. An interesting pattern in temperatures where large portions of the western valleys are in the mid 30s, while DCA has dropped into the 20s (and teens in typical rural areas). It appears a combination of a weak surface pressure trough and downslope flow instigated by the shortwave has kept winds elevated west of the Blue Ridge. Water vapor imagery shows a mountain wave pattern, although so far, only a transient strip of cirrus has developed ahead of the trough axis. Simulated synthetic satellite suggests a larger standing wave cloud could develop this morning, although confidence is reduced since its current verification is overdone. Assuming the cirrus don`t interfere too much, continued warming is expected today. Have gone close to a MOS blend, which brings 50s up to the US-50 corridor. If yesterday is any indication, a few degrees may need to be tacked on...though downslope flow will be lighter today. For tonight, the high will remain along the Gulf Coast. A few cirrus may cross the area while winds become light. Have lows ranging from the mid 20s to lower 30s. It could be colder in spots if prolonged decoupling occurs, as dew points will still be in the teens/lower 20s. && .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... High pressure will continue eastward off the southeast coast into the Atlantic over the weekend, resulting in continued west/southwest flow and mild weather. Saturday will be (aesthetically) the better day of the weekend with plentiful sunshine and temperatures into the 50s across much of the area (maybe even 60 for Charlottesville- Fredericksburg). Low level moisture return around the high will begin to encroach on the Appalachians by Saturday night. Given the shallow nature, any precipitation likely remains west of the divide and would likely be very light rain. There`s still a chance temperatures could be just below freezing, supported by forecast soundings but less so in GEFS/SREF/WPC FZRA probabilities. However, continued warm advection will end any limited ice threat by daybreak Sunday (if not much sooner). Any light rain will likely remain west of the Allegheny Front Sunday. However, lower clouds may spread east of the mountains as well, particularly northern parts of the area. Combined with surface flow that may become more southeast than southwest, temperatures will likely be a little cooler than Saturday. The question is just by how much, and where the dividing line between 45-50 and 55-60 degree temperatures will be. A backdoor cold front may drop into northeastern parts of the area by Sunday night, which could lead to some light rain or drizzle. Low temperatures will be in the upper 30s. && .LONG TERM /MONDAY THROUGH THURSDAY/...
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At the start of the long term, a warm front will be lifting north across the region as low pressure strengthens to our west across the Corn Belt. Southerly flow will be enhanced south of the front, and temperatures stand a shot at reaching the 60s across a decent portion of the area on Monday. A little rain is possible as the front lifts north, most likely near the PA border and most likely earlier in the day. EC and to a lesser extent the GFS is now hinting that a triple point low may try to develop along the approaching cold front as it crosses our region later Monday night. This would enhance the rainfall and increase the risk of potential convection. Will need to monitor this in case it looks like a low-end squall line with heavy rain and gusty winds could develop as the system passes. Monday night will remain mild, at least through the time of cold frontal passage, with temps staying in the 50s, perhaps even low 60s, much of the night. The front pushes east of the region as we head through Tuesday, with steady or falling temps and rain ending. Some upslope rain/snow showers may linger along the Alleghany Front through the whole day, however. Despite the falling temps, they should stay fairly mild for late January, with readings unlikely to drop severely. This is due to the incoming high behind the system having more of a Pacific origin, versus the recent high pressures which have dropped southeast from Canada. Therefore, while Wednesday and Thursday look to be dominated by this high, it should only be close to normal for late January, versus the recent cold outbreaks which dropped temps 10-20 degrees below normal each time. With the high overhead, Wednesday and Thursday should turn out dry with some sun as well.
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&& .AVIATION /09Z FRIDAY THROUGH TUESDAY/... No aviation concerns are expected through Saturday as high pressure moves along the Gulf Coast. Winds will be between west and south, and generally less than 10 kt. Low level moisture return begins Saturday night and definitely Sunday into Sunday night. Best case is scattered to broken low VFR, although SREF indicates decent probabilities of MVFR by Sunday, especially northern parts of the area (metros included), and a greater chance of IFR by Sunday night with possible light rain/drizzle. Cig and vis restrictions look likely by Monday night into Tuesday as a cold front moves across the region, bringing periods of rain. && .MARINE... Winds will remain between west and south through the weekend as an area of high pressure moves from the Gulf Coast off the southeast coast. Mixing (both due to warm air temperatures and a subsidence inversion aloft) will likely keep winds less than 15 kt, although there could be some near-SCA gusts near the shore of the northern Bay today and again Saturday. SCA looking likely at some point Tuesday as a cold front crosses the region. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...RCM NEAR TERM...ADS SHORT TERM...ADS LONG TERM...RCM AVIATION...ADS/RCM MARINE...ADS/RCM

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