Area Forecast Discussion
Issued by NWS Sterling, VA

Current Version | Previous Version | Text Only | Print | Product List | Glossary On
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
-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS61 KLWX 300758 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 358 AM EDT Fri Sep 30 2016 .SYNOPSIS...
-- Changed Discussion --
Upper level low pressure over Kentucky will begin to lift northward towards the Great Lakes today and into the weekend. The low will pass by to the north early next week as it moves offshore. High pressure will build into the area late in the weekend and into early next week.
-- End Changed Discussion --
&& .NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
Have canceled the remaining portions of the Flash Flood Watch...as the threat for repeated rounds of heavy rain has ended over these areas. Current radar analysis shows pockets of light...to at times moderate...rainfall across much of the area. Drizzle has also been observed in areas where showers are not occurring. Expect these trends to continue into today...as persistent onshore flow remains. Ensemble/Deterministic guidance is in fairly good agreement with bringing another round of showers (and perhaps some isolated thunder) into the southern portions of the forecast area by mid-to- late afternoon. HRRR-TLE shows decent probabilities for an inch over a three hour period with this activity...with very low probabilities of 2 inch/hr rates. Thus...expect only a localized flooding threat if training convective cells manage to develop. Strong wind field remains...so a few stronger storms are possible across the south. Elsewhere...including the DC/Balt metros...wet weather continues...though, mainly in the form of patchy light showers or drizzle. Some moderate showers could work into the area by this evening as the activity across the south possibly pivots into the area. Rain rates with this activity would be rather light.
-- End Changed Discussion --
&& .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
-- Changed Discussion --
Upper-level low will continue to track northward towards the Great Lakes and then pass by to our north as it moves eastward toward the weakening ridge over the Atlantic Saturday into Sunday. Impacts associated with the low will begin to lessen Saturday...with only a few spotty showers lingering (mainly across the northern half of the CWA). By 00Z Sunday...dry slot expected to have finally worked its way through the area...as frontal boundary pushes off to the east. This will finally eliminate precipitation chances into Sunday...for all but upslope areas along the western slopes. Drying out Sunday with highs in the M/U70s.
-- End Changed Discussion --
&& .LONG TERM /MONDAY THROUGH THURSDAY/...
-- Changed Discussion --
Surface high pressure remains over New England through mid- week...with mostly dry and seasonable conditions across the Mid- Atlantic. Highs in the 70s early next week...though, as onshore flow develops around the surface high by mid-week...high temperatures will fall into the 60s. Tropical Cyclone Matthew expected to be located somewhere in the Atlantic by mid-week. Extreme run-to-run inconsistencies and model spread continues...as is usually the case this far in advance. Far too early to discuss possible impacts to Mid-Atlantic region.
-- End Changed Discussion --
&& .AVIATION /08Z FRIDAY THROUGH TUESDAY/...
-- Changed Discussion --
Upper level low will continue to impact the area through Friday with onshore flow causing low ceilings at most terminals. Periodic drizzle/showers through tonight...with IFR conditions prevailing. Though, brief LIFR ceilings are possible in the heaviest showers. Improving conditions Saturday as upper-low begins to lose its influence over the area. Prevailing VFR conditions Saturday through early next week as high pressure builds into the area.
-- End Changed Discussion --
&& .MARINE...
-- Changed Discussion --
Solid (to high-end) SCA winds currently being realized across much of the Chesapeake Bay...with winds closer to SCA criteria up the tidal Potomac. HRRR/NAM/GFS BUFKIT soundings show decent mixing continuing through early evening...with SCA winds remaining. Extended the SCA headline for the Chesapeake Bay into early Saturday morning...as guidance indicates SCA gusts lingering awhile longer there. Gradient relaxes for all locations by early Saturday...with winds remaining below SCA criteria into early next week as high pressure builds into the area.
-- End Changed Discussion --
&& .TIDES/COASTAL FLOODING...
-- Changed Discussion --
Water levels running up to 2 feet above astronomical predictions early this morning. With the continued east wind, do not expect much change. If anything, the departures may increase slightly. As a result, we are in the midst of a prolonged tidal flooding event. For the most part, minor flooding is being realized within a couple hours of high tide. However, there are a couple of exceptions, namely St. George Island and Annapolis, where moderate flooding has occurred (or in Annapolis` case is forecast). Confidence is sufficient to extend most Advisories and Warnings for both tide cycles on Saturday. There are a couple of exceptions: (1) the mid tidal Potomac, where the shoreline is high (will only carry Advisories through the tide cycle tonight); (2) Southern Baltimore, where the tide cycle occurs Saturday evening (will only go through Saturday day). Skill in water level forecasting isn`t great beyond 36 hours. Consequently, have a Coastal Flood watch for Saturday evening in St. Marys and Anne Arundel Counties, where moderate is still forecast, but will less confidence. On the upper tidal Potomac, at least minor tidal flooding should occur through at least Saturday evening. Am awaiting the latest model output from the HEC-RAS, and will decide from there. A gradual decline in water levels should transpire Saturday night and Sunday. It is unclear at this time whether an additional tide cycle would be affected. There is plenty of time to figure that out.
-- End Changed Discussion --
&& .LWX WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
DC...Coastal Flood Warning until midnight EDT tonight for DCZ001. MD...Coastal Flood Advisory until midnight EDT tonight for MDZ013. Coastal Flood Warning until noon EDT Saturday for MDZ014-017. Coastal Flood Watch from Saturday afternoon through Saturday evening for MDZ014-017. Coastal Flood Advisory until 8 PM EDT Saturday for MDZ016-018. Coastal Flood Advisory until 2 PM EDT Saturday for MDZ011. VA...Coastal Flood Advisory until midnight EDT tonight for VAZ052>055. Coastal Flood Advisory until 8 PM EDT Saturday for VAZ057. WV...None. MARINE...Small Craft Advisory until 2 AM EDT Saturday for ANZ530>534- 538>543. Small Craft Advisory until 7 PM EDT this evening for ANZ535>537.
-- End Changed Discussion --
&& $$ SYNOPSIS...MSE NEAR TERM...MSE SHORT TERM...MSE LONG TERM...MSE AVIATION...MSE MARINE...MSE TIDES/COASTAL FLOODING...HTS

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