Area Forecast Discussion
Issued by NWS Sterling, VA

Current Version | Previous Version | Graphics & Text | 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. --
047 FXUS61 KLWX 231902 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 302 PM EDT Fri Sep 23 2016 .SYNOPSIS...
-- Changed Discussion --
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.
-- End Changed Discussion --
&& .NEAR TERM /THROUGH SATURDAY/...
-- Changed Discussion --
At the surface, high pressure currently resides over the Ohio Valley, providing a light north to northwesterly downslope flow across our region. To the north, a cold front is stretched from near Chicago eastward to Portland Maine, heading southward. Aloft, northwesterly flow dominates as we sit between a ridge of high pressure over the lower Mississippi Valley and a deep trough over eastern Canada. Aloft, a shortwave will drop southeastward but the forcing will miss our region to the northeast. Otherwise the northwesterly flow will just become a bit stronger and more northerly as the trough digs to our northeast while the ridge remains in place to our southwest. At the surface, high pressure to our west will slide southward as the cold front crosses our area late tonight and early Saturday. With little forcing or moisture, in most areas we only expect some increased winds (perhaps a few gusts to 20 mph or so) as they shift from northwest to north or northeast...and some clouds...which will hang around for a great deal of Saturday before gradually clearing from north to south in most of the area. Lows tonight will stay elevated ahead of the front, but highs tomorrow 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.
-- End Changed Discussion --
&& .SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY NIGHT/...
-- Changed Discussion --
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.
-- End Changed Discussion --
&& .LONG TERM /MONDAY THROUGH FRIDAY/...
-- Changed Discussion --
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.
-- End Changed Discussion --
&& .AVIATION /19Z FRIDAY THROUGH WEDNESDAY/...
-- Changed Discussion --
VFR through Saturday. Patchy fog may develop near KCHO tonight (low chance)...should be fog-free elsewhere. Front will cross the area late tonight and early Saturday with a wind shift to a more northerly direction along with perhaps a gust or two to 20 knots...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.
-- End Changed Discussion --
&& .MARINE...
-- Changed Discussion --
Light winds rest of today with sunshine. Clear most of tonight but clouds and wind increase late with cold front crossing area. Expect a few gusts to 20 knots so have SCA in place thru Saturday morning. Winds should die down 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.
-- End Changed Discussion --
&& .TIDES/COASTAL FLOODING...
-- Changed Discussion --
Anomalies remain elevated. Should not be a big concern next 24 hours as winds shift more northerly though Annapolis will be close and will need monitoring. As winds shift more easterly Sunday and then southeasterly Monday...anomalies could increase and risk of tidal flooding may rise.
-- End Changed Discussion --
&& .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... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory from 2 AM to 2 PM EDT Saturday for ANZ530>534-537>543. && $$ SYNOPSIS...RCM NEAR TERM...RCM SHORT TERM...RCM LONG TERM...DFH AVIATION...RCM/DFH MARINE...RCM/DFH TIDES/COASTAL FLOODING...RCM CLIMATE...DFH

USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.