textproduct: Seattle/Tacoma

SYNOPSIS

A weather system will move onshore today across northwest Oregon, resulting in lingering showers for Western Washington. Unsettled conditions will continue on Tuesday for light precipitation. A frontal system will move into the area late Tuesday into Wednesday, bringing lowland rain, mountain snow, and breezy conditions. Cooler conditions favored midweek into the weekend.

SHORT TERM /TODAY THROUGH WEDNESDAY/

An upper-level low pressure system continues to spin offshore towards northwest Oregon early this morning. As the system pushes east today, expect lingering shower activity. A weak shortwave will drop down early Tuesday keeping conditions unsettled. A frontal system associated with a colder air mass will will move south from British Columbia into Washington late Tuesday into Wednesday. This system will bring lowland rain, mountain snow, cooler temperatures, and breezy winds. Snow levels are expected to drop Tuesday evening into Wednesday morning to 2500-3500 ft. These lower snow levels will introduce snow to the passes. Latest NBM guidance has trended slightly higher for snowfall amounts. At the moment, guidance suggests the passes may see between 4-6 inches and higher mountain peaks may receive 8-13 inches by Wednesday evening. Additionally, there is a slight chance of thunderstorms on Wednesday for the lowlands, with probabilities currently between 10-15%. As for winds, latest guidance has wind gusts peaking between 20-25 mph. In the wake of the cold front passing on Wednesday, high temperatures are expected to only peak into the upper 40s to low 50s.

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LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/

There is generally good agreement between ensembles that the upper level low will deepen offshore Thursday through late in the week, lowering the chances for precipitation over Western Washington. Cooler temperatures are favored to continue into the weekend. High temperatures in the upper 40s to low 50s. Low temperatures will be in the 30s, with upper 20s possible in the usual colder spots. Ensemble members are evenly split on the upper-level pattern on Sunday. Some members favor a trough over the Pacific Northwest, while others favor a transient upper level ridge.

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AVIATION

South to southeasterly flow aloft as an upper level low sinks southward along the coast before starting to push inland over northern OR today, before shifting northwesterly as the system moves further east. SUrface winds this morning largely light and variable with speeds less than 5 kts. Those showing slightly faster speeds ranging 4-8 kts have a more east to northeasterly direction, such as HQM, OLM and BLI. Most terminals expected to shift southerly by early afternoon although speeds largely remaining around 5 kts or slightly less.

Lower cigs mainly tied to where precip persists this early morning. VFR conditions being reported by the East Sound Terminals while much of the Olympic Peninsula has MVFR to IFR conditions. With the coast being close to the center of the upper low, a mix of VFR to MVFR conditions are present there but as latest radar shows another band of precip reaching the coast by mid-morning, a shift to more MVFR cigs there is likely. Short-lived widespread low-end VFR conditions expected in the early afternoon, but with plenty of low level moisture and a shift to onshore flow, MVFR conditions throughout W WA expected to develop this evening with MVFR/IFR conditions tonight into Tuesday.

KSEA...VFR conditions this morning, although brief reductions to MVFR/IFR will be possible in any rain that moves through. Low- end VFR conditions expected this afternoon and evening, but expect conditions to drop to MVFR overnight with the return of onshore flow and abundant moisture in the low levels. Some guidance is hinting at IFR conditions emerging in the overnight hours (roughly a 15% chance), however confidence in this scenario remains low at this time.

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MARINE

A weakening surface low will move onshore over the northern Oregon coast today, flipping winds back to onshore. Another frontal system will reach the waters on Wednesday as its associated low moves into the region and southward along the coastal waters. This will likely bring the next round of headlines to portions of the area waters as well as the return of offshore flow to the waters through the second half of the week.

Seas generally 3-6 ft today before briefly building back up to 7-9 ft near midweek. They will then subside once more to 4-6 ft Thursday and remain there through the weekend.

SEW WATCHES/WARNINGS/ADVISORIES

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