Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
Issued by NWS Seattle/Tacoma, WA
362 FXUS66 KSEW 172223 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 323 PM PDT Tue Sep 17 2024 .SYNOPSIS...Clouds and rain chances increase across the region tonight ahead of an approaching frontal system. Lingering rain showers into Wednesday, especially in a potential Puget Sound Convergence Zone, as the upper trough pushes eastward. A break in the rain and clouds for Thursday, but this will be brief as additional rounds of unsettled conditions will continue through the weekend and into early next week. && .SHORT TERM /TONIGHT THROUGH FRIDAY/...A rather cool and cloudy afternoon is underway across Western Washington, as temperatures hover around 60 degrees. NWS radar depicts increasing rain offshore and extending eastward into the Olympic Peninsula already. This will continue to advance eastward through the night, with the highest rainfall accumulations (around half an inch) expected west of Puget Sound and in the Cascades. The bulk of the actions pushes through the region overnight, but as the upper trough pushes south and east, expect strengthening onshore flow to bring some light drizzle or rain through the morning. Meanwhile, some lingering showers are likely to develop in a Puget Sound Convergence Zone early Wednesday. Expect a lull in the clouds and rain showers late Wednesday through Thursday with weak high pressure somewhat building over the region. The next disturbance is likely to arrive (or at least approach) by Friday, bringing another increase in cloud cover and cooler temperatures. .LONG TERM /SATURDAY THROUGH TUESDAY/...The weekend will continue with a decidedly fall-like pattern as zonal flow aloft sets up and keeps the door open for a series of disturbances through the first half of next week. This will maintain abundant cloud cover and rain at times, while temperatures hold below seasonal normals. Will need to monitor the evolution of these features as subtle shifts in the storms can yield significant shifts in where the moisture sets up and the resulting impacts in clouds and temperatures. This is reflected in the probabilistic NBM guidance exhibiting some quite large spreads in values as we get into the early part of next week. 12 && .AVIATION...West to southwest flow aloft will become light east/northeasterly tonight. At low levels onshore/southerly flow will ease overnight with widespread light and variable winds lingering into Wednesday morning. Widespread MVFR ceilings across the interior lowlands this afternoon may continue to lift this afternoon and evening with periods of VFR conditions - prevailing conditions will likely linger in the 2500 to 3000 foot range. For the coast conditions will remain 800 to 1200 feet. Areas of light rain along the coast will linger into the evening. KSEA...VFR ceilings 3000 to 3500 will linger into the evening then lower overnight dipping to 1000 to 1500 feet between 10 and 14z with a 70% chance of ceilings below 1000 feet by 14Z. Southwesterly surface winds 5 to 7 knots will ease and become light and variable after 06Z. && .MARINE...A weak surface low passing to the southwest this afternoon and evening will result in gusty easterly winds over the coastal waters into this evening before easing overnight. Offshore surface high pressure returns Thursday into Friday helping boost northwesterlies and possible small craft advisory levels with combined seas rising to 7-9 feet late in the week, particularly across the outer coastal waters. && .SEW WATCHES/WARNINGS/ADVISORIES... WA...None. PZ...None. && $$