textproduct: Seattle/Tacoma

SYNOPSIS

Western Washington remains on the back side of an upper level ridge through the weekend with low level onshore flow continuing. The ridge moves east Monday as a weak system moves by to the north. An upper level trough develops offshore on Tuesday and remaining through Friday. A dissipating system arrives Wednesday with another possible weak system on Friday.

SHORT TERM /TODAY THROUGH MONDAY/

There is extensive marine stratus throughout Puget Sound this morning with westerly flow aloft. Expect limited visibilities in central and southern Puget Sound due to fog and mist. More appreciable scattering of the marine layer will occur after 19Z.

Not much going on weatherwise this weekend. Western Washington on the backside of an upper level ridge with westerly flow aloft over the area. In the lower levels light onshore flow. Stratus will be tough to get rid of along the coast with just some late day sunshine. Highs mid 60s coast and mid 60s to lower 70s inland.

Little change in the pattern tonight and Sunday. Another round of late night and morning low clouds with patchy fog over the interior while the coast stays mostly cloudy. Sunshine in the afternoon over the interior will put highs in the mid 60s to mid 70s. Highs along the coast in the mid 60s. It will be a cool morning Sunday with lows in the mid 40s to lower 50s.

A few changes Monday but the forecast will remain the same. Upper level ridge moves off to the east while a weak system moves inland well north of the area. Weak low level onshore flow in the lower levels keeping the morning clouds afternoon sunshine scenario intact. Highs remaining in the mid 60s to mid 70s with lows in the mid 40s to lower 50s. Felton/21

LONG TERM /MONDAY NIGHT THROUGH FRIDAY/

Models in good agreement through Thursday with an upper level trough offshore. Dissipating system moving into the area Wednesday for a slight chance of showers over the northern portion. GFS brings the trough into the area Friday while the ECMWF keeps the trough offshore. Ensembles have enough solutions with light precipitation to put slight chance pops in the forecast. Slow cooling trend with highs in the mid 60s to lower 70s Tuesday dropping to the lower to mid 60s by Friday. Lows remaining in the mid 40s to lower 50s. Felton

AVIATION

Westerly zonal flow will prevail aloft today. Marine stratus is firmly entrenched throughout Puget Sound, except for KBLI where CLR conditions prevail. Lower cigs will struggle to dissipate before 17Z and will likely break up more appreciably after 19Z-20Z. VFR in the afternoon is expected. Today, southerly winds are expected until 18Z-19Z when winds will turn WNW, becoming more NNW between 20Z-00Z. Another round of low stratus clouds looks likely tomorrow morning, setting in after 12Z and lasting through much of Sunday morning.

KSEA...LIFR cigs presently at the terminal this morning, with limited visbys beyond 3SM and cigs as low as 300 ft. Oscillations between LIFR and IFR cigs are likely between now and 19Z as the stratus remains firmly in place. General scattering and improvement isn't expected before 19Z-20Z and will be gradual. Winds will be light out of the SSW this morning, becoming more westerly around the same time as the cig and vis improvements. A switch to a light northerly is forecast after 20Z. Speeds will be 5 kts or less throughout the period. There is a 30% chance of IFR (50% chance of MVFR) cigs returning to the terminal early tomorrow morning around 13Z.

21

MARINE

Weak onshore flow will continue into next week as broad high pressure remains over the offshore waters. Weakening frontal systems moving by to the north through next week will help to increase onshore flow, allowing for increased chances for Small Craft Advisory conditions each evening with westerly pushes through the Strait of Juan de Fuca. Pushes will begin to increase tonight and Sunday evening, but will most likely remain below thresholds. Chances for meeting Small Craft thresholds rise to 50-80% by Monday evening, with slightly lower chances on Tuesday evening.

Seas remain 3 to 5 ft until Monday as incoming swell rises seas to around 6 to 8 ft. Seas remain in that range through mid-week.

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FIRE WEATHER

While general low-level onshore flow will maintain cloud cover and higher humidities across the region, expect to see some light north or northeast winds near the Cascades tonight through Sunday, with Sunday afternoon RH values approaching the 30-35% range. Given the overall pattern, concerns remain minimal through much of the week ahead, with cooler temperatures and rain chances returning by the middle of next week.

SEW WATCHES/WARNINGS/ADVISORIES

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