textproduct: Seattle/Tacoma

SYNOPSIS

A trough will keep the pattern unsettled through much of the week. Cool temperatures will allow for rain and snow showers to continue in the lowlands through much of the week, especially overnight and early morning hours. Mountain snow will also be possible, but remain light through the week. Potential increases for a more significant system to produce more substantial precipitation, breezy winds, and also warmer temperatures.

SHORT TERM /TODAY THROUGH THURSDAY/

A mid/upper level low has dug its way southward from Alaska yesterday, and has parked itself off the coast of Washington. It will likely remain out there and rotate slowly inland towards the end of the week, keeping the pattern unsettled with the trough pattern.

The radar has been active this morning. The main activity has been along the Pacific Coast, with a heavier area of showers (snow and possible graupel) pushed through Westport and Ocean City, and continues to track northward in far west Grays Harbor County. Additional showers are moving their way across the remainder of Grays Harbor County up into far west Thurston/West Mason Counties this morning, and will continue to track northward across the Olympics. The ensembles continue the current shower activity through the morning, with a couple HREF ensemble members showing potential for a band of showers (potentially containing snow) moving up the I- 5 corridor through Olympia this morning. With the temperatures overnight dropping into the low 30s/upper 20s in this area, the potential exists for slick surfaces across the portion of I-5 (as with other roads that remain wet overnight with cool temperatures). Use caution if driving and/or walking outdoors for possible slick surfaces. The winter weather advisory as of now will continue through noon for the US-101 corridor from Crescent Lake through the Lower Chehalis Valley (including Hood Canal-Willapa and the Black Hills).

With the trough again in place, this will keep a slight chance/chance of showers/snow showers in place through midweek. The current wave of showers will rotate around the low, with additional development to the south expected to wrap around across the rest of the interior/Cascades later this morning into the afternoon/evening. A couple HREF/NAM members enhance some of the precipitation this evening/overnight across the north Olympics, and some of the Cascade Foothills in Snohomish/King Counties, but given the showery nature of this activity, this will continue to be hit or miss in terms of coverage.

Precipitation chances increase again regionwide going into Wednesday as the low begins to pivot inland (still wrapping a couple of troughs on the west side of the low). There will be some Fraser River outflow overnight Wednesday/Thursday morning, which looks to cool temperatures a few degrees more (this would concern the north interior especially Whatcom County with lows in the mid 20s). Highs are still expected to reach the low to mid 40s during the next few days. Mountain snow impacts remain relatively minimal through midweek with light snow rates.

LONG TERM /THURSDAY NIGHT THROUGH MONDAY/

The aforementioned trough will begin to fill/move in late Thursday, which will drop the precipitation chances going into the evening. A couple of the models throw in a ridge on Friday, but a majority of the ensemble members throw in another trough late Friday into next weekend. While the ridge may not be enough to keep the region dry for a day, temperatures will begin to rise a few degrees, reaching the low 50s again towards the end of the weekend. The main concern is going to be potential for heavier precipitation, with the increase of southerly flow bringing in additional moisture into the region. This includes the potential for heavy mountain snow (especially in the Olympics). While the threat of flooding remains low at this time, this may change depending on how the moisture/snow levels track with this system.

Additionally, the low pressure offshore is expected to generate higher seas, which may translate to larger waves across the Pacific Coast Saturday into Sunday, potentially impacting some of the beaches.

HPR

AVIATION

Southwest flow aloft maintaining scattered showers. Expect ceilings to continue to widely vary with MVFR/IFR in heavier showers and higher MVFR to VFR in the areas that are dry. Could still see some mixing snow in the showers in or around the terminals, but with surface temperatures warming during the day this will mostly be melting either before or upon reaching the surface. Southeast surface winds becoming southerly through the day, but remaining rather light (around 5 kt or less). Another round of showers overnight with again the potential for some snow mixing in the showers, with a decreasing trend from 17z onward.

KSEA...Ceilings remain VFR this morning with showers around the region but largely avoiding the terminal area. Passing showers could bring brief MVFR conditions but this remains a very low probability for the majority of the day. Some increased showers again tonight as temperatures cool brings the potential for snow mixing with rain overnight, but again little to no snow accumulation expected. Winds remain generally light through Wednesday, becoming southeast this morning and increasingly southerly later tonight.

MARINE

A trough will remain offshore through at least Thursday before moving inland. Showers will be possible at times over the waters (some of which may be heavy enough to reduce visibilities briefly). Winds are expected to remain light as the low tracks inland, switching from southerly to northerly. In the short term however, the main concern is seas, with a small craft advisory continuing for the coastal waters, Grays Harbor Bar (and now the west Strait of Juan de Fuca) through Wednesday morning for 10-13 ft seas. The seas will drop to 6-8 ft Wednesday as the low begins to propagate inland. A stronger system may impact the region next weekend, with the potential for a few gale gusts in the outer coastal waters, small craft winds in a majority of the waters, and seas increasing up to 16-18 ft on Sunday.

HPR

HYDROLOGY

No river flooding is expected during the next seven days.

SEW WATCHES/WARNINGS/ADVISORIES

WA...Winter Weather Advisory until noon PST today for Foothills of the Western and Southern Olympic Peninsula-Lake Crescent Area Including US 101-Lower Chehalis River Valley- Southern Hood Canal-Willapa and Black Hills.

PZ...Small Craft Advisory until 10 PM PST this evening for Coastal Waters From Cape Flattery To James Island Out 10 Nm- Coastal Waters From James Island To Point Grenville Out 10 Nm-Coastal Waters From Point Grenville To Cape Shoalwater Out 10 Nm-Grays Harbor Bar-West Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory until 4 AM PST Wednesday for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm- Coastal Waters From James Island To Point Grenville 10 To 60 Nm-Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm.