textproduct: Seattle/Tacoma

SYNOPSIS

Mostly dry and mild conditions will continue through much of next week across western Washington as an upper level ridge remains situated over the region. Troughing is on track to return by next weekend, bringing cooler conditions and increased chances for mountain showers.

SHORT TERM /TONIGHT THROUGH TUESDAY NIGHT/

An onshore push is well underway this evening with the marine layer marching inland to just west of Shelton as of 830 PM PDT. Stratus will fill in across much of the interior by early Monday morning. As a result, high temperatures tomorrow will cool several degrees under mostly cloudy skies. Tuesday remains a virtual carbon copy before upper ridging rebuilds Tuesday night into Wednesday with low level flow turning more northerly again. Sunshine returns Wednesday and Thursday. Current forecasts are on track. Previous discussion follows with updated aviation section. 27

Northerly flow aloft has brought another dry day across western Washington, with temperatures on track to peak several degrees above normal in the upper 60s to lower 70s. High pressure will continue to build onshore tonight into Monday, generating onshore flow that will allow low clouds to develop along the coast and filter inland towards the Puget Sound Monday morning. The onshore flow will bring in cloudy skies across western Washington, limiting temperatures into the upper 50s to lower 60s. This system will also bring a slight chance of light showers along the coast and over the mountains. More of the same will continue on Tuesday, with a degree or two of cooling under mostly cloudy skies.

LONG TERM /WEDNESDAY THROUGH SUNDAY/

An upper level ridge building offshore will drift closer to the Washington coastline on Wednesday and Thursday, bringing in a warming trend with clearing skies. The ridge axis will shift inland on Thursday, bringing the warmest temperatures of the week. Highs will peak in the upper 60s to mid 70s across the lowlands, resulting in areas of Minor (Yellow) HeatRisk east and south of the Puget Sound.

Models have come into slightly better agreement heading into next weekend, showing split flow developing aloft as a closed low drops southward along the coast and the upper level ridge progresses east of the Rockies. This will likely maintain mild temperatures across the region, with ensembles maintaining a slight chance of mountain showers next weekend.

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AVIATION

North to northwesterly flow aloft continues through Monday with troughing over the interior West and upper ridge offshore. VFR conditions for the interior, with MVFR/IFR stratus along the coast. Onshore flow tonight into Monday will result in stratus spreading into the interior through this period. Predominantly MVFR/IFR cigs for the interior sites late tonight through Monday morning, with IFR along the coast. Cigs will slowly improve into VFR midday Monday into early Monday afternoon for interior locations, with MVFR continuing along the coast. Southerly winds will increase tonight into Monday.

KSEA...VFR conditions into early tonight. Stratus will move into the interior late tonight, with lower end MVFR cigs expected to develop around 09-10z. MVFR cigs then remain through 18-19z before improvements to VFR in the afternoon. There also remains approximately a 30% probability of IFR cigs, peaking between 10 to 15z Monday. S/SW surface winds through the TAF period ranging between 5 to 10 kts. JD

MARINE

High pressure continues over the coastal waters, with lower pressure to the east. The flow returns to onshore this week with weak pushes through the Strait of Juan de Fuca. The strongest push in the guidance is Monday evening, but the probability of winds exceeding 20 kt remains low. Low ceilings in the coastal waters Monday morning (with pockets of fog) may lower visibilities at times to mariners. The next potential system may bring breezy winds over the coastal waters around Friday.

Seas for Sunday hold around 4-6 ft, and increase to 6-8 ft for the remainder of the week. There is potential for 9-10 ft seas Thursday and Friday depending on the track of the next system.

HPR

HYDROLOGY

No river flooding is expected over the next 7 days.

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...None.