textproduct: Seattle/Tacoma

SYNOPSIS

Upper level ridge centered offshore building tonight and remaining in place into Friday. The ridge will weaken Saturday. Surface high pressure out ahead of an approaching front will increase the low level onshore flow Sunday for cloudier and cooler weather. Next system arriving Memorial Day. Another upper level ridge will build into British Columbia Tuesday or Wednesday.

SHORT TERM /TONIGHT THROUGH FRIDAY NIGHT/

No updates to forecast are anticipated this evening. Previous discussion follows with update to aviation portion. 27

Satellite imagery shows some strato cumulus banked up again the Central and Southern cascades this afternoon. Another area of stratus over the Olympics with mostly clear skies elsewhere. Temperatures at 3 pm/22z were in the mid 50s to mid 60s.

Low level onshore flow decreasing overnight with upper level ridge building offshore. By sunrise light flow in the lower levels with patchy fog developing in the fog prone locations like the Lower Chehalis and Snohomish river valleys. The fog will be shallow and dissipate soon after sunrise. Lows in the 40s.

Upper level ridge building offshore, temperatures warming aloft and light flow in the lower levels will give Western Washington a warmer day Thursday. Patchy morning fog and stratus will be gone by mid morning. Highs in the mid to upper 60s coast and 70s to lower 80s inland.

Not much change in the pattern Thursday night into Friday. Low level onshore flow a little stronger with stratus developing along the coast spreading inland in the early morning hours. The marine layer will be shallow and not get east of Puget Sound. Under sunny skies highs again in the 70s to lower 80s inland. Morning clouds keeping highs in the 60s along the coast. Lows Thursday night in the mid 40s to lower 50s.

Upper level ridge offshore weakening Friday night with increasing low level onshore flow. Stratus making it into the interior around 12z. Lows in the mid 40s to lower 50s. Minor HeatRisk both Thursday and Friday. Felton

LONG TERM /SATURDAY THROUGH WEDNESDAY/

First two days of the holiday weekend look dry. Stratus dissipating back to the coast Saturday. Minor HeatRisk continues. Upper level ridge out ahead of an approaching front will increase the onshore flow Sunday for more cloud cover and cooler temperatures.

Models having a hard time with the timing of the next system. Operational runs hold off rain over the interior until late Monday. Ensembles show this solution is in the minority with a majority of the ensembles with a faster eastward progress of the front. This is in the current forecast with a chance of rain Sunday night and rain spreading over the area on Memorial Day. Highs in the 60s and lower 70s Saturday lowering to the mid 50s to lower 60s Monday.

AVIATION

VFR conditions in place over W WA this evening with scattered high clouds in place. These conditions are expected to prevail for most through the TAF period. The exception will be the Pacific coast where the marine layer will reform overnight into Thursday morning. Latest satellite imagery is already starting to show a bank of stratus just off the coast. These stratus should remain mostly confined to the coastline, through there's a low chance it could get as far east as SHN and CLM (15-25% chance). Elsewhere should remain clear (less than 15% chance of MVFR or lower). Mostly clear skies will continue tomorrow with cirrus clouds streaming overhead. Surface winds NW 5-10 kt will ease after sunset, becoming light NE or variable overnight. Winds once again switch to NW 5-10 kt during the day Thursday.

KSEA...VFR conditions through the TAF period with high clouds overhead. Winds NW 8-10 kt becoming NE around 5 kt overnight. Winds Thursday return to NW 5-10 kt.

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MARINE

High pressure will remain situated offshore through the rest of the week, keeping north/northwest winds prevailing across the coastal waters. Diurnally driven pushes through the Strait of Juan de Fuca each afternoon are expected, though the weakest day looks to be Thursday before the winds reach back up to small craft advisory thresholds. The strongest winds will remain farther offshore, but out near the 60 NM border winds may reach up to 20-25 kt at times. Small Craft conditions look more probable for the outer coastal waters Friday night into Saturday as high pressure edges closer onshore. This will also allow for stronger onshore flow, with the strongest being Saturday which has the potential (30-50%) to reach gale force through the Strait of Juan de Fuca. A frontal system remains on track to traverse the area on Monday, which will bring more widespread small craft conditions to most of the coastal and interior waters.

Seas remain around 6 to 8 ft through Friday. Seas look to pick up and steepen with the winds late Friday into Saturday and reach near 10 ft through the outer coastal waters. Seas then ease on Sunday before the incoming low pushes seas up to 10 to 13 ft Monday into Tuesday.

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HYDROLOGY

The daily hydrology discussion has ended until the start of the next rainy season; it will only be updated during this time as needed.

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory until 11 PM PDT this evening for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca.