textproduct: Seattle/Tacoma

SYNOPSIS

Drier conditions to start the week as upper-ridging builds into the region. It won't be long lasting as the next weather system arrives on Tuesday with lowland rain and mountain snow. The pattern is slated to remain active through the rest of the week with additional rounds of precipitation.

SHORT TERM /TODAY THROUGH TUESDAY/

Weak surface high pressure over W WA with mostly calm winds observed so far this morning. Clearing skies and light surface winds has resulted in the development of patchy fog - can't rule out areas of freezing fog for locations in the Chehalis River Valley, W Whatcom lowlands, etc. For today, an upper low well offshore will gently track eastward before positioning over N California/S Oregon by the evening. Concurrently, broad ridging is over the NE PAC as higher heights build over the PNW. Conditions are slated to remain dry into Monday as the ridge axis begins to position more overhead. High temperatures are to top out in the upper 40s to near 50 F with overnight lows cooling into the 30s each night.

An upper-ridge continues over the PNW on Monday night but pattern progression looms. The next front looks to arrive on Tuesday with widespread lowland rain and mountain snow. Snow levels will range between 4,000 to 5,000 ft

LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/

The pattern looks to remain active through the week with rain, mountain snow, breezy winds at times. In these rounds of snow, the chances for reaching advisory amounts are highest (40-50%) in the North Cascades but with the most likely snow levels hovering around 4000 ft impacts to the Cascade passes look to be limited. Ensembles diverge a bit into the weekend with differences emerging with about an equal split between continued active pattern or a return to drier conditions under higher heights.

AVIATION

A flat upper level ridge positioned to the southwest part of the state will keep northwesterly flow aloft going today. Surface winds for most terminals remaining out of the north with some variances to the NE or NW at times. Speeds to remain typically around 5-10 kts, however some spots may see speeds ease overnight to 5 kts or less.

Widespread VFR conditions persist early this morning, with exceptions at OLM and BLI with periods of mist and lowered visbys. Expect VFR cigs throughout the rest of the TAF period past 17Z for the lower terminals. Northerly surface winds 7-10 kts becoming light after 00Z.

KSEA...VFR conditions likely to persist through the TAF period. While a slight chance exists for MVFR cigs at or near the terminal early Sunday morning, have opted to continue FEW to SCT 020 through 16Z with very little confidence in an MVFR deck. Northerly winds generally running 5-10 kts, easing below 8 kts after 00Z.

21

MARINE

High pressure continues to develop with northerly winds over much of the waters and weakly offshore component driving winds through the Strait of Juan de Fuca. Seas are generally around 4 to 6 ft over the coastal waters today.

Expect the next round of advisory conditions Tuesday as the next frontal system reaches the waters, with continued winds into the second half of the week. At this point, headlines are likely to be capped at SCA criteria for wind, with seas coming up to around 7 ft Tuesday night into Wednesday. Seas will build again later in the week, getting a little choppy around midweek in conjunction with the stronger winds and then building to around 10 ft by Friday.

21

HYDROLOGY

No river flooding is expected during the next seven days.

SEW WATCHES/WARNINGS/ADVISORIES

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