Two strong and fast moving frontal systems will move across Western Washington tonight and early Saturday morning. These fronts will be followed by a period of strong westerly flow to the south of a storm system moving into British Columbia Saturday afternoon and Saturday night. There is a threat of strong winds, heavy rainfall, minor flooding on more flood-prone rivers, heavy mountain snowfall, and coastal flooding over portions of the area tonight through Saturday night.
1. A High Wind Watch is in effect for tonight through Saturday for the north and central Washington coast and for the Admiralty Inlet area.
2. A winter storm watch is in effect late tonight through Saturday night for the Cascades and Olympics above 2000 feet.
3. A flood watch is in effect for Mason, Snohomish, King and Pierce counties late tonight through late Saturday night.
4. A coastal flood watch is in effect for the north and central Washington coast Saturday afternoon through late Saturday night.
Chuck Wallace with the Grays Harbor Emergency Management agency tells us some of the watches may be converted to Warnings or Advisories during the day on Friday, so keep a close eye on latest forecast updates from the National Weather Service.
1. Concerning the threat of strong wind: South winds will increase tonight across all of western Washington and will turn to the west on Saturday. Across most of the lowland areas, winds are expected to range from 20 to 35 mph with gusts to 50 mph. Damaging winds to 40 mph with gusts to 55 mph, from both the south and the west, are possible on the coast and around the Admiralty Inlet area.
2. Concerning the threat of heavy rainfall and possible flooding: Rain will develop today and will become heavy at times tonight through early Saturday. The snow level in the mountains will increase from around 3500 feet to over 6000 feet tonight then will fall back to 3000 feet on Saturday. During the warmer period tonight, rainfall amounts of 4-6 inches are likely in the Olympics and 3-5 inches in the Cascades. This amount of rain will cause rapid rises on area rivers, and more flood prone rivers like the Skokomish, Stillaguamish, Tolt, and Puyallup could see minor flooding late tonight into Saturday or Saturday night.
3. Concerning the threat of heavy mountain snow: Precipitation in the mountains above about 3000 or 3500 feet will begin as snow today. Snow levels will rapidly rise to 5000 feet in the northern Cascades and to around 6500 feet in the central Cascades and Olympics. Snow levels will fall back to 3000 feet on Saturday and 2000 feet Saturday night. Five to ten inches of snow are likely Saturday with another foot on Saturday night. The mountain snow will be accompanied by windy conditions. It will be particularly windy on exposed mountain ridges in the back country.
4. Concerning coastal flooding: An area of storm force winds offshore will produce 25 to 30 foot waves that will move onto the Washington coast Saturday afternoon and Saturday night. While tides are expected to be relatively low during the large wave event, there is a potential that large and energetic waves will give some flooding to low-lying coastal communities like Westport, portions of Ocean Shores, and La Push. The large waves will produce dangerous surf and beach erosion.
Concerning strong wind: confidence is high that very windy conditions will develop across the area. Confidence in the potential for damaging wind on the coast and in the Admiralty Inlet Area tonight and Saturday is slightly lower. If a weaker low, as forecast by some forecast models, tracks north of Vancouver Island, it will get windy but the wind speeds will remain below 40 mph.
Concerning heavy rain: Confidence is high that around 4 inches of rain will fall tonight into early Saturday in the Olympics and up to 3 inches will fall in the Cascades. If the air mass remains cooler over the northern Cascades, minor flooding will be less likely north of King County. If rainfall amounts overnight are higher, some rivers could see moderate flooding.
Concerning heavy mountain snow: Confidence is high that a period of heavy snow will occur in the Cascades Saturday afternoon and Saturday night. The confidence of heavy snowfall in the Olympics around Hurricane Ridge is lower. If the air mass remains slightly cooler tonight in the northern Cascades than what is currently expected, there is a threat of heavy snowfall around Mount Baker tonight in addition to the heavy snowfall Saturday and Saturday night.
4. Concerning coastal flooding: At this time it appears that the highest threat of big waves hitting the coastline is late Saturday afternoon and Saturday night during a period of lower tides. There is a risk that the offshore storm will be stronger and farther south than currently expected, waves will move in a few hours sooner, and that waves will be bigger than currently expected. If this occurs, the threat of coastal flooding in low lying beach communities will be higher.