Storm Update: Heavy Rain, Gusty Winds Ahead

Update by 5 PM Friday with latest details & forecast.

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We are less than 24 hours from the start of the first significant storm of the season. Heavy rain, gusty winds, and a chance of thunderstorms are all in the cards.

The rain shield of the incoming system will reach the coast early Friday morning, with rain falling in the Puget Sound area soon after. Expect some rain in the morning, then a potential break in the rain during the afternoon.

Then, on Friday evening, the real action begins. An area of very moist air will move over Western Washington, with a current of air heavy with water vapor directed right at the Puget Sound area.

The UW forecast above is for 8 PM Friday, as heavy rain will be falling in the Puget Sound lowlands. 

Below are 24 hour totals from 5 AM Friday to 5 AM Saturday from the UW model.

From Seattle southward, expect 24-hour totals of 1-2 inches. Up to 2.5 inches near Olympia, and massive amounts of 6-7.5+ inches in the Olympics & Cascades. Notice the prevalent rain shadow northeast of the Olympics. These areas, including North Seattle and Everett, will receive lesser totals of 0.3-1 inches.

This isn’t the end…the rain continues well into Sunday, just becoming more showery. Additional rainfall of 0.5-1.1 inches is expected through Sunday evening.

Make sure that your gutters and storm drains are cleared before the heaviest rain arrives. If you haven’t done this yet, you have until Friday evening!

Now for the wind. Since my last blog post, the forecast winds have increased. Below are 5 forecast model predictions. (How to read this: large numbers=sustained winds, small numbers=gusts, arrows=wind direction)

This forecast (for Federal Way) shows winds gusting 30-40 mph from Friday afternoon/evening through early Saturday morning. Conditions remain breezy (gusts 20-30 mph) through Saturday evening.

Expect slightly stronger winds near Puget Sound, and winds gusting 45-50 mph on the coast and from Admiralty Inlet northward. (Wind Advisory in effect for those areas).

Regarding winds, since this is the first storm of the season, trees are fully loaded and therefore more vulnerable to damage. Add on the fact that many trees have been weakened by this summer’s extreme heat, and the threat for tree damage is higher. Be prepared for scattered power outages and damaged trees.

There is one more threat worth mentioning…thunderstorms.

Behind the cold front that moves through Friday night, the air will be unstable. The best chance for thunderstorms will be midday Saturday to Sunday evening. CAPE instability values of 200-600 will be present over the Lowlands (relatively high for our area). Values of 600+ are possible at times along the WA & OR Coasts.

Wow! A lot of active weather is heading our way! Expect things to calm down by Sunday evening, with dry weather likely by Monday. Below is a recap from NWS Seattle.

Enjoy the storm & stay safe!