Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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 41 42 43 44 45 46 47 48 49 50
-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
171 FXUS66 KSEW 250343 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 843 PM PDT Sat Mar 24 2018 .SYNOPSIS...A weak upper trough will bring a few showers tonight. A series of weak weather systems will bring rain at times later Sunday through Tuesday night. An upper ridge will bring drier and warmer weather Wednesday and Thursday. Colder air will try to spread back into Western Washington with a few showers next Friday and Saturday. && .SHORT TERM...A weak upper trough will be over the area tonight. Isolated showers are expected to mainly end this evening with the loss of diurnal heating. Increasingly moist northwest flow will develop across the area on Sunday. Spotty light rain is possible by afternoon, mainly over the mountains and north coast. Light rain should develop all areas Sunday night as a weak front moves onshore. The aforementioned front will basically fizzle over the area on Monday for a drippy day. There will be some drying later Monday with showers becoming more confined to the mountain. Another weather system will move through the area Monday night/Tuesday for more wet weather at times. The last in a series of short waves in the northwest flow aloft looks to bring an uptick in rain again Tuesday night. Below normal highs will continue Sunday but they should creep up each day early next week and approach normal by midweek. Schneider .LONG TERM...Previous discussion...The offshore upper ridge will sharpen modestly near 130W-135W on Wed, which should be enough to lighten or diminish the stratiform rain. Thursday appears to have the best chance for a dry day, but confidence was only high enough for a full-on dry forecast over the southern half of the forecast area. The ridge will flatten and dissipate on Thursday night with a resumption of stronger west-northwest flow aloft. Upper height falls will develop over B.C. and spread southward into the Pacific NW next Saturday. Colder air will gradually filter back into the region. A few convective showers are possible as the air mass gets colder and a bit more unstable. Haner && .AVIATION...A weak upper trough will be over the area tonight with light west to southwest flow aloft. West to northwest flow aloft will increase on Sunday. A front will move into the area Sunday night. At the surface, weak high pressure will be over the area tonight and early Sunday. Southerly flow will increase on Sunday ahead of an approaching front. Slightly unstable air this evening will become stable later tonight. There are some patches of VFR low clouds floating around this evening but mostly just mid and high clouds across the area. Models cross sections and statistical guidance suggest there will be areas of MVFR ceilings and patchy IFR low clouds Sunday morning over the central and south sound. KSEA...Mostly high clouds tonight. A few hours of MVFR ceilings are likely Sunday morning. Moisture will begin to increase at all levels Sunday evening as a front reaches the area. Light wind tonight will become south 5-10 knots Sunday. Schneider && .MARINE...Weak high pressure will be over the waters tonight and early Sunday. A frontal system will move through the area later Sunday and Sunday night bringing small craft advisory strength winds to most waters. Another frontal system will affect the waters Monday and Tuesday. Onshore flow will prevail Wednesday and Thursday with high pressure offshore and lower pressure inland. Schneider && .HYDROLOGY...River flooding is not expected for the next 7 days. && .SEW WATCHES/WARNINGS/ADVISORIES... WA...None. PZ...None. && $$ is the U.S. government's official web portal to all federal, state and local government web resources and services.