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. --
678 FXUS61 KLWX 230800 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 400 AM EDT Mon Apr 23 2018 .SYNOPSIS...
-- Changed Discussion --
High pressure will move offshore today. A low pressure system will bring unsettled weather to the region tonight through the middle of next week. A brief ridge ridge of high pressure will build in later in the week, ahead of the next low pressure system toward the weekend.
-- End Changed Discussion --
&& .NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
High pressure will move off of the East Coast today as a cut- off low pressure system moves up the East Coast from the Southeast U.S. Winds will persist out of the southeast ahead of the low pressure system. Clouds will thicken through the day today. Temperatures will modify some into the middle 60s. Some light rain could overspread the region from the southwest to northeast later today into tonight. The first areas to encounter this rain will be the central Shenandoah Valley.
-- End Changed Discussion --
&& .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
-- Changed Discussion --
As the cut-off low and a couple of pieces of upper level energy move into the mid-Atlantic region Tuesday, additional rounds of light to moderate rain will develop and overspread most of the region. This rain should gradually taper to showers Tuesday night and end from southwest to northeast. However, the ending time may be delayed as the next upper level disturbance will be quick on the heels of the Monday night and Tuesday low pressure system. Temperatures will be about 5 to 10 degrees cooler Tuesday due to cloud cover and rainfall and about 5 to 10 degrees milder Tuesday night due to the same two factors. Low pressure will be moving northeast away from the area Wednesday morning, leaving a chance for some residual showers in its wake. Another quick moving shortwave will move through Wednesday evening into Thursday morning. Some showers will be possible with this system as well, especially Wednesday night. Temperatures Wednesday will be below average, thanks to the cloud cover and precipitation expected over the area.
-- End Changed Discussion --
&& .LONG TERM /THURSDAY THROUGH SUNDAY/...
-- Changed Discussion --
The area of low pressure will depart off to the northeast on Thursday leading to dry conditions and slightly below normal temperatures. The forecast becomes much more uncertain for Friday. Several different shortwave disturbances will interact as they move across the CONUS between now and Friday. The high number of these complex interactions lend themselves to high uncertainty in the forecast for Friday through Sunday. The GFS forms a surface low in the Southeast Thursday Night out ahead of a compact shortwave, and then proceeds to track that low up the East Coast on Friday giving us a round of rain. On the other hand, the Euro keeps the shortwave and attendant area of low pressure suppressed to the south and weaker in nature. Roughly half of the members in the 00z GEFS give us over a tenth of an inch of rain, and only a few members of the 12z EPS gave us over a tenth of an inch with this system. So, to summarize...there`s at least a chance for rainfall on Friday, but it`s an uncertain forecast to say the least. Another upper-level trough and associated weakening cold front will approach the area from the west this weekend. Most model guidance keeps us dry with the passage of this front, but some light precipitation can`t be ruled out. Temperatures this weekend are expected to remain slightly below average.
-- End Changed Discussion --
&& .AVIATION /08Z MONDAY THROUGH FRIDAY/...
-- Changed Discussion --
VFR conditions expected through Monday with light and variable winds, becoming southeast 5 to 10 knots this afternoon and tonight. Winds southeast around 10 knots Monday and Monday night. MVFR conditions are possible at the CHO terminal Monday night with some light rain approaching from the southwest. MVFR conditions possible at all terminals Tuesday and Tuesday night due to light to moderate rain. Winds east 10 to 15 knots Tuesday becoming northeast 5 to 10 knots Tuesday night. Clouds will stick around for much of the day on Wednesday Sub-VFR conditions possible during this time. VFR conditions are likely on Thursday. Conditions could potentially drop to sub-VFR on Friday if a coastal low were to develop, but the forecast is highly uncertain at this point. Conditions will likely return to VFR for the weekend.
-- End Changed Discussion --
&& .MARINE...
-- Changed Discussion --
No marine hazards expected overnight through Monday. Winds southeast 10 to 15 knots Monday. Small craft advisory conditions possible Monday night through Tuesday night. Winds southeast becoming east 10 to 15 knots with gusts up to 20 knots Monday night and Tuesday. Winds becoming northeast 10 to 15 knots gusts to 20 knots Tuesday night. As the storm system from Tuesday exits Wednesday morning, some gusty winds are possible across the marine areas, with SCA criteria winds possible during that time. Gusty winds also possible Thursday morning, but not looking as strong as on Wednesday at this time. No marine hazards are expected Thursday through Sunday at this time.
-- End Changed Discussion --
&& .HYDROLOGY...
-- Changed Discussion --
While we had significant rain a week ago, its been pretty dry since then. That said, 1-2 inches of rain looks likely across the region Monday night through Wednesday, which could lead to some minor hydrology issues and cause river and stream rises, potentially up to flood stages. Will be closely monitoring this for potential need of any flood watches over the next day or so.
-- End Changed Discussion --
&& .TIDES/COASTAL FLOODING...
-- Changed Discussion --
As low pressure approaches the waters from the southeastern U.S. late Monday into Tuesday, a persistent onshore flow will develop. This will yield increasing tidal anomalies, and the possibility of coastal flooding toward the middle part of the work week.
-- End Changed Discussion --
&& .LWX WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory from 1 PM this afternoon to 6 AM EDT Tuesday for ANZ534-536-537-543.
-- End Changed Discussion --
&& $$ SYNOPSIS...KLW NEAR TERM...KLW SHORT TERM...KLW LONG TERM...KJP AVIATION...KLW/KJP MARINE...KLW/KJP HYDROLOGY...KLW TIDES/COASTAL FLOODING...KLW

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