textproduct: Seattle/Tacoma

SYNOPSIS

An upper level low will continue to spin offshore, maintaining showers across the region this week. Another frontal system crosses around Wednesday, bringing additional rounds of heavier snow in the mountains and rain in the lowlands. Temperatures cool later in the week through the weekend with drier conditions setting up for most.

SHORT TERM /TODAY THROUGH WEDNESDAY NIGHT/

Widespread showers continue across the region this afternoon with the bulk of the moisture continuing to be aimed across the southern portions of the area. While this will bring some additional snowfall to the higher elevations, only minor additional roadway accumulations are expected at the Cascade passes given the warmer surface temperatures and decreasing showers. Heights rise a little into Tuesday which should largely constrain showers to the mountains. Northwesterly flow develops into Wednesday which will again introduce some shower chances through the day. A passing disturbance into Wednesday night, however, will bring the focus for additional moisture. While the strongest moisture transport looks to the be the north of the local area, this will bring the potential for additional mountain snow. The focus of this looks to be generally from I-90 northward and most likely snowfall amounts are around 6 inches at the Cascade passes with this system. 12

LONG TERM /THURSDAY THROUGH SUNDAY/

Ensemble guidance continues to favor a west or northwest flow pattern across the region late this week. Initially, the focus will remain in the North Cascades, with US 2 northward through Mt. Baker likely seeing increasing snowfall amounts into the weekend. However, showers are expected to continue across most of the area with snow levels around 3000 ft or so. Looking into the weekend, heights rise a little bit and likely limit the potential for showers across much of the area. This will allow for some clearing and temperatures to trend cooler, with overnight lows approaching or dropping below freezing for many locations (especially away from the city centers). 12

AVIATION

Showers and stratus linger over much of the region this afternoon with southwesterly flow aloft continuing. Portions of Puget Sound could see continued showers this afternoon as more develop along the coast and move east. Brief reductions in vis and cigs are possible, though generally VFR outside of precipitation. As the weather system continues moving east, showers will persist before drying out more tomorrow. Expect a shift from southerly surface flow to NNE winds after 02Z. Speeds will be light, picking up tomorrow morning to around 10 kts after 12Z.

KSEA...VFR with breezy southerly winds at the terminal presently. Over the next few hours, vicinity showers and/or -RA is possible as additional bands of rain move onshore and push into Puget Sound. A shift to NNE winds is still forecast to occur after 02Z and linger throughout the rest of the TAF period. High pressure will dry things out into tomorrow, but some lower MVFR stratus cigs (020-025) are likely to occur tomorrow morning before becoming VFR in the afternoon. Expect winds to elevate tomorrow morning between 9-11 kts through 18Z before easing thereafter.

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MARINE

Seas remain around 10 ft and relatively steep with dominant period around 9 to 10 seconds over the coastal waters this afternoon. The SCA for the coastal waters has been extended through this evening as a result. Otherwise, seas continue to steadily but slowly subside over the next day or two. Meanwhile, winds Tuesday night through the Strait of Juan de Fuca will increase, with around a 50% chance of advisory strength winds. The more significant increase in winds is likely to be Wednesday night through early Thursday as a disturbance slides across the area and increases the westerly winds through the Strait. Local gale gusts are possible (30-40%), but confidence remains low in the precise timing. Otherwise, expect building seas late in the week over the coastal waters, with a return to 10-15 ft waves likely (80% chance). 12

HYDROLOGY

No river flooding is expected during the next seven days.

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory until 4 PM PST this afternoon for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm- Coastal Waters From Cape Flattery To James Island Out 10 Nm-Coastal Waters From James Island To Point Grenville 10 To 60 Nm-Coastal Waters From James Island To Point Grenville Out 10 Nm-Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm-Coastal Waters From Point Grenville To Cape Shoalwater Out 10 Nm.