textproduct: Seattle/Tacoma

UPDATE

Satellite imagery shows high clouds over the southern portion of the area with mostly clear skies to the north. Temperatures at 9 PM/05Z were in the upper 30s to mid 40s.

Upper level low west of the Oregon California border will move east overnight eventually weakening and moving inland Sunday evening. This will keep some high cloud cover from about Olympia southward through Sunday. Upper level ridge over the area Sunday night will shift east Monday opening the door to a weather system for Tuesday. Current forecast has the trends covered. No updates this evening. Previous discussion below with updated aviation section.

SYNOPSIS

Upper level high pressure builds over the region and holds through the weekend into the start of next week. The ridge breaks down early in the week, with a return to mountain snow and lowland rain late in the next week.

SHORT TERM /TONIGHT THROUGH MONDAY NIGHT/

An upper level ridge remains overhead the region, and much of the west coast today. A jet core to the north and a trough offshore to the southwest is keeping the flow northerly across the region. With high pressure in control, the weather is largely quiet this weekend into early next week. The cloud coverage will decrease this evening into Sunday/early Monday. The best chance of fog development is Sunday morning in the south interior, where the combination of cooler temperatures/lighter winds may lead to dense fog. Otherwise the next chance of precipitation will be a 30-40% chance of PoPs along the coast Monday afternoon with a small trough perturbation. Otherwise, high temperatures will increase into the mid and upper 50s in the lowlands Sunday/Monday, with lows Sunday and Monday morning in the 30s. Winds will be out of the north/northeast through the weekend, and could get a tough breezy in spots, but otherwise will remain in the 5-10 mph range.

HPR

LONG TERM /TUESDAY THROUGH SATURDAY/

Expect a shift in the pattern to develop on Tuesday with the next front pushing into the region. Reasonably good agreement with the majority (70-80%) of ensemble members bringing the initial front into the region early Tuesday. The pattern looks to remain active through the week with rain, mountain snow, breezy winds at times as the pattern remains active through the late stages of next week. 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 into Sunday. Surface winds for most terminals remaining out of the north with some variances to the NE or NW at times. Exceptions are CLM and HQM, where winds are taking more of an easterly direction. Speeds to remain typically around 5-10 kts, however some spots may see speeds ease overnight to 5 kts or less.

VFR conditions in place over W WA this evening, although a very visible line of clouds is impacting the south Sound and points south. This will allow for MVFR cigs OLM and HQM overnight into Sunday morning /with potential for isolated IFR cigs/ while remaining terminals should stay VFR...although some FEW/SCT low clouds will be possible. Widespread VFR conditions expected to return by late Sunday morning.

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, confidence is not there to warrant inclusion in the forecast. Northerly winds generally running 5-10 kts.

18

MARINE

High pressure continues to develop with breezy northerly winds over much of the waters and weakly offshore component driving winds through the Strait of Juan de Fuca. A few gusts in the afternoon may get to around 20 kt, but in general conditions will remain below advisory thresholds. Meanwhile, seas are generally around 5 to 6 ft over the coastal waters this weekend. 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, though, the likelihood for gales remains quite low, less than 10-15%. 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.

HYDROLOGY

No river flooding is expected during the next seven days.

SEW WATCHES/WARNINGS/ADVISORIES

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