Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
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Issued by NWS Seattle/Tacoma, WA
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-- Discussion containing changed information from previous version are highlighted. --839 FXUS66 KSEW 220835 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 135 AM PDT Wed May 22 2024 .SYNOPSIS...-- Changed Discussion --Showers will decrease today as an area of low pressure over the region moves eastward. Weak high pressure aloft will produce drier and somewhat warmer conditions on Thursday before another upper level trough drops into Western Washington Friday into Saturday for cool and unsettled conditions. A weak ridge of high pressure will lead to milder temperatures early next week, but will not prevent a chance of showers from remaining in the forecast.-- End Changed Discussion --&& .SHORT TERM /TODAY THROUGH FRIDAY/...-- Changed Discussion --Convergence zone activity continues over Snohomish and north King counties early this morning as moderate onshore flow remains in place in the wake of a cold front that moved across the area early yesterday evening. The trailing upper trough axis will slip east of the Cascades by late this morning and low level onshore gradients will ease allowing shower activity to dissipate by afternoon. Except for a chance of evening showers in the Cascades, drier conditions will develop tonight as northerly flow aloft develops once again ahead of weak ridging offshore. A flattening ridge axis will slide onshore on Thursday for mainly dry weather and a very modest warming trend. The next in a seemingly endless series of upper troughs slides southward from British Columbia on Friday for an increasing chance of showers and cooler temperatures. .LONG TERM /SATURDAY THROUGH TUESDAY/...The aforementioned trough progresses southeastward across the area Friday night into Saturday keeping the threat of showers in the forecast and temperatures below normal. A subtle shift in the synoptic pattern begins early next week as upper ridging builds across the Great Basin and Intermountain West while a broad upper trough deepens over the Gulf of Alaska. The proximity of the ridge should contribute to somewhat warmer temperatures Monday into Tuesday, but a sequence of systems brushing the region moving into British Columbia will likely keep precip chances in the forecast...especially over the Olympic Peninsula and North Interior portions of the CWA. 27-- End Changed Discussion --&& .AVIATION...-- Changed Discussion --Mainly MVFR to IFR with low stratus overspreading much of the area early this morning. Convergence showers impacting KPAE will slowly shift eastward before another round of showers pushes into the area under northwest flow aloft. Brief improvement to low-end VFR early this morning will likely be short-lived, with ceilings filling in through the early afternoon. Conditions will improve heading into the evening, returning to VFR across most of the terminals. The marine layer will keep the coast in low ceilings through early Thursday. KSEA...MVFR ceilings behind a cold frontal passage will continue through the morning with southwest surface winds 10-15 kt with gusts as high as 30 kt slowly easing to below 10 kt by the afternoon. VFR conditions return by the early afternoon as cloud cover decreases. Forecast models show a brief shift to north/variable flow between 20z- 00z before southwest flow returns, but confidence is low on the exact timing and direction. AL-- End Changed Discussion --&& .MARINE...-- Changed Discussion --Strong post-frontal winds will continue throughout the morning and into the afternoon before easing, with a Gale Warning for portions of the outer waters and Small Craft Advisories for the rest of the seas. Alongside the strong winds, seas will rise to 12 to 16 ft offshore especially over the northern coastal zones throughout the morning before the NW swell shifts southward. Waves will be steep with short period waves dominating. Conditions will calm tonight into Thursday before another frontal system passes through area waters on Friday. This will likely bring another round of elevated seas and breezy winds. AL-- End Changed Discussion --&& .SEW WATCHES/WARNINGS/ADVISORIES...-- Changed Discussion --WA...None. PZ...Small Craft Advisory until 5 PM PDT this afternoon for Coastal Waters From Cape Flattery To James Island Out 10 Nm-Coastal Waters From James Island To Point Grenville Out 10 Nm- Coastal Waters From Point Grenville To Cape Shoalwater Out 10 Nm-Grays Harbor Bar. Small Craft Advisory until 5 AM PDT early this morning for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca-West Entrance U.S. Waters Strait Of Juan De Fuca. Gale Warning until 11 AM PDT this morning for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm-Coastal Waters From James Island To Point Grenville 10 To 60 Nm. Small Craft Advisory from 11 AM this morning to 5 PM PDT this afternoon for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm-Coastal Waters From James Island To Point Grenville 10 To 60 Nm. Small Craft Advisory until 8 PM PDT this evening for Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm.-- End Changed Discussion --&& $$