Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 261904 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 304 PM EDT Mon Sep 26 2016 .SYNOPSIS...
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A cold front will pass through the area tonight into Tuesday. An upper-level low will impact the area during the middle to latter portion of the week.
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&& .NEAR TERM /THROUGH TUESDAY/...
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At present...high pressure is centered in the western Atlantic not far south of Cape Cod. A warm front is trying to advance northeastward across western Maryland, eastern West Virginia and western Virginia. A cold front extends from Lake Erie southward across the upper Ohio Valley towards the lower Mississippi Valley, also moving east. Much of West Virginia, far western Maryland and a few parts of western Virginia have entered the warm sector, but most of the CWA is still northeast of the warm front with plenty of low stratus clouds and a gusty southerly wind. For the small portion of the CWA in the warm sector, temps have risen into the 80s with some sunshine and scattered thunderstorms are developing not far to the west. These will move through over the next few hours on their way to the cool wedge north of the front. The main band of showers associated with frontogenesis along the cold front is still back in Ohio. These will move east overnight as well. The warm front appears unlikely to actually reach most of the CWA...with the cold front likely to occlude and lift the warm air off the ground as it crosses our region. Thus...while there is a marginal risk of severe weather in the warm sector...we do not expect this threat to reach most of the CWA tonight. Some thunder may however persist as the showers move across the area. Lows will be mild in the 60s with the clouds and showers. The front slows to a crawl on Tuesday as it becomes oriented parallel to the upper level flow just to our southeast. Thus...while our northwestern zones should dry out...the risk of showers lingering into much of Tuesday increases as one heads southeastward...with showers likely most of the day in southern Maryland. Where the sun breaks out...highs should rebound into the 70s.
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&& .SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
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A great deal of uncertainty regarding the details of the weather during the middle portion of the week as a large closed low settles southward into the eastern United States and induces cyclogenesis on the stalled frontal boundary near our region. Tuesday night should still be mostly dry as the influence of the upper low is yet to be very significant. By Wednesday, the low is likely to start inducing the development of a low pressure system somewhere in our region to the east or south. A position further east would likely result in a drier day Wednesday into Wednesday night, while if the low develops further south along the front, rain becomes more likely as we head towards Wednesday night, especially across eastern portions of the CWA. Temps are uncertain given the uncertain rain/cloud forecast, but more 70s would seem probable. Guidance is more solid on the low pressure that develops either redeveloping further west or being pulled west by the upper low on Thursday, with most guidance showing at least some rain across the region. It should be noted that while the GFS is fairly dry with more showery weather, the more southwesterly storm development depicted by the ECMWF nows shows several inches of rain. Flash flood guidance being very high thanks to the recent period of dry weather (many areas having seen less than half an inch of rain in the last month), the ground is likely to be able to absorb a fair amount of water. We will have to monitor any potential for excessive rainfall in a relatively short period of time however. Highs on Thursday are more uncertain still but may be stuck in the 60s.
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&& .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
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Looks like guidance is starting to agree on the evolution of the upper level low. GFS and ECMWF have been consistent on its solution - the upper level low is located to over the Great Lakes - tracking slowly south and later retrograding. In general, GEFS members agree on this solution as well, with some members moving it faster north and away from our region. Location of this system will have impacts on the forecast, but for now it seems that there will be a chance of showers Thursday night into Saturday as moisture is advected into our region... and then drying out sometime on Saturday and into Monday with high pressure building in.
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&& .AVIATION /19Z MONDAY THROUGH SATURDAY/...
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Low clouds have been very persistent today with MVFR cigs widespread...and IFR around CHO earlier. At this point think the low cigs are likely to persist rest of the day before showers and perhaps a thunderstorm moves across the region tonight. IFR is expected at times overnight with the rain both CIGs and VIS. Some improvement likely on Tuesday as the front shifts southeastward. Low pressure development Wednesday-Thursday brings potential for SUB-VFR conditions again, but uncertainty with timing and exact conditions is high at this time. Sub-VFR conditions possible Thursday night and maybe into Saturday as upper level disturbance could bring showers into the region. Conditions becoming VFR Saturday into Sunday as high pressure builds in.
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&& .MARINE...
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Southerly channelling ahead of the approaching cold front is bringing small craft conditions to most of the waters. These will continue into the evening before gradually winding down from northwest to southeast after midnight as the front moves through. Lighter winds likely Tuesday-Wednesday then new storm developing across the region may result in a return of SCA conditions late Wednesday into Thursday. Small craft advisory possible Thursday night and into Friday night with near or above the threshold. Winds will be diminishing Saturday and into Sunday below the small craft advisory threshold.
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&& .TIDES/COASTAL FLOODING...
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Southeast winds have increased today into tonight and tidal anomalies have been fluctuating. The next high tide cycle this afternoon will be the lower of the two...and right now no flooding is expected with it. There is a better chance for minor flooding during the high tide cycle tonight into early Tuesday just ahead of the front. Tidal Anomalies should drop later Tuesday behind the cold front.
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&& .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory until 6 AM EDT Tuesday for ANZ530>543. && $$ SYNOPSIS...RCM NEAR TERM...RCM SHORT TERM...RCM LONG TERM...IMR AVIATION...IMR/RCM MARINE...IMR/RCM TIDES/COASTAL FLOODING...BJL/RCM

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