Area Forecast Discussion
Issued by NWS Sterling, VA

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071 FXUS61 KLWX 240112 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 912 PM EDT Fri Sep 23 2016 .SYNOPSIS... A cold front will cross the area late tonight and early Saturday. High pressure returns to the region late Saturday and Sunday before moving off the coast Monday. A cold front will slowly pass through Tuesday into Wednesday. High pressure will return for late next week. && .NEAR TERM /THROUGH SATURDAY/...
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Latest surface analysis suggests that the cold front stretches across southern New England to the New York-Pennsylvania border. There is minimal moisture of forcing associated with it, so the most that can be expected is a band of clouds and north winds. Latest indications are that will happen just before sunrise Saturday. So most of the night will be mostly clear and calm. Although there will be some radiational cooling, a warmer start to the night and dewpoints in the 60s indicate that lows Saturday morning will be warmer than this (Friday) morning. Clouds will hang around for a great deal of Saturday before gradually clearing from north to south in most of the area. Temperatures should be generally 5 degrees cooler in our southern regions and at least 10 degrees cooler further north across the metro and close to Pennsylvania. As the front stalls in central/southern Virginia, some weak instability and flow becoming more upslope may cause a few showers to form tomorrow afternoon in west-central Virginia.
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&& .SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY NIGHT/... The front will nudge a bit further south of our region Saturday night as high pressure from Canada builds further southeast. For much of our area this will clear things out and result in the coolest night since before Summer started...with widespread 50s and perhaps some high 40s. However...in west-central Virginia...upslope flow may be moist enough to generate some low clouds...drizzle or spotty showers. This should gradually dissipate during the day Sunday as temps warm up but clouds may linger. Further north and east across the metro...most areas should be mostly sunny and cool on Sunday with highs also expected to be the coolest since before Summer started...with low 70s common and some areas failing to crack 70. Sunday night looks relatively similar to Saturday night...with upslope clouds/drizzle/showers possible in west-central Virginia...but mostly clear and cool conditions further north and east across the metro. && .LONG TERM /MONDAY THROUGH FRIDAY/... Mid/upper-level ridge axis will move over the area Monday as surface high pressure departs into the western Atlantic. 850 mb temperatures will begin to warm but easterly to southeasterly onshore flow at in the low levels will lead to increased cloud cover and cooler temperatures. Model solutions diverge significantly after Monday. The uncertainty seems to stem from the strength of ridging downstream over the western Atlantic and how quickly it allows an incoming trough to approach from the west. The GFS has exhibited significant run-to-run timing differences and GEFS/EC members also exhibit large timing spread. The timing will also affect the trajectory and duration of moisture return which will impact just how much rain we are able to see as the trough approaches during the middle of next week. Models continue to diverge for late next week with some indicating the trough departing while others develop a cutoff low near or just east of the CWA. At this time, it appears the highest precipitation chances would be in the Tuesday to Wednesday time frame with a gradual return to fair weather by the end of next week. After a brief cool down behind the mid-week front/trough, another warming trend seems likely by the end of next week as strong ridging builds over the lower Mississippi/Tennessee River Valleys. && .AVIATION /01Z SATURDAY THROUGH WEDNESDAY/...
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VFR through Saturday. Its still possible that patchy fog may develop near KCHO tonight. While the fog coverage has increased in the grids, there have been no changes made to the TAF sites at this time. Front will cross the terminals late tonight and early Saturday with a wind shift to a more northerly direction along with a few gusts...along with some clouds at around 5k ft or so. Clouds may linger near CHO Saturday night and Sunday but should clear elsewhere. Sub-VFR possible with lower ceilings as a result of onshore flow Monday, then with possible showers ahead of an approaching front Monday night through Tuesday. Southeasterly winds around 10 knots Monday will gradually veer around to the southwest by late Tuesday.
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&& .MARINE...
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Winds from the south this evening, but at speeds below 10 kt. There may be a slight increase in wind speeds ahead of an approaching cold front, but latest guidance suggests that 20 kt gusts will hold off til the northerly flow behind the frontal passage. That will take place during the hours around sunrise Saturday. Therefore, have dropped the Small Craft Advisory for the overnight hours, but will maintain it for the morning-midday hours Saturday. Winds should diminish Saturday afternoon and generally sub-SCA winds after that through Sunday night. Southerly channeling/Small Craft Advisory level gusts along with an increasing threat for showers are anticipated ahead of an approaching front late Monday into Tuesday.
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&& .TIDES/COASTAL FLOODING...
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Anomalies remain elevated, but caution stages appears to be where sensitive locations will top out with the incoming tide. Saturday`s tides should be a little bit lower due to northerly flow across the estuary. However as winds shift more easterly Sunday and then southeasterly Monday...anomalies could increase once again, and risk of tidal flooding may rise.
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&& .CLIMATE... Unusually warm weather has persisted over the area for quite some time. Autumn-like temperatures will finally make an appearance over the weekend likely bringing low temperatures at DCA below 60 degrees for the first time since June 9th, or 105 days ago. The record most consecutive days at or above 60 degrees in the Washington DC area is 112 set in 2012. && .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory from 6 AM to 2 PM EDT Saturday for ANZ530>534-537>543.
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&& $$ SYNOPSIS...RCM NEAR TERM...HTS/RCM SHORT TERM...RCM LONG TERM...DFH AVIATION...HTS/RCM/DFH MARINE...HTS/DFH TIDES/COASTAL FLOODING...HTS CLIMATE...DFH

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