Fourth of July Weekend Forecast: Cool & Showery

 FastCast—Saturday, July 2 to Monday, July 4:

A cloudy and cooler pattern will prevail for Western Washington through July 4th. Expect mostly cloudy conditions with a chance of showers late in the evening on Saturday. Highs will be in the upper 60s to low 70s are expected on Saturday. There is a chance of thunderstorms in the mountains, Eastern Washington, and near the foothills. There is a chance of severe thunderstorms in NE Oregon, SE Washington, and the Central Idaho Panhandle on Saturday. There is a very slight chance that some storms may wander into the lowlands. Showers continue on Sunday, with cool conditions as well. Highs will only reach the low to mid 60s, and most of the state will receive rain. 0.1-0.2 inches will fall in the southern half, and 0.2-1.1 inches will fall in the northern half (up to 2.5 inches in the North Cascades). July 4th will be a tad warmer, with highs rebounding a bit into the upper 60s. Showers are possible (especially in the mountains), but will likely taper by afternoon. Expect clouds to slowly clear by evening, and mostly clear skies are expected for the Seattle area around fireworks time. Additionally, there will be very little wind overnight, making it hard for firework smoke to clear out of the area.

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A rainy few days is ahead for Washington state, especially the northern half. Most rain will fall from late Saturday through midday Monday. The European model forecast below shows how much rain to expect.

In the lowlands, expect the most rain to fall north of Seattle, totaling 0.25-0.75 inches. The mountains and the northern tier of Eastern Washington will receive 0.25 to 1.1 inches, with totals of 1.5-2.5 inches possible in the North Cascades.

There is a marginal risk of severe thunderstorms on Saturday for parts of the Inland NW. See the Storm Prediction Center graphics through Pivotal Weather below.

The dark green from Central Oregon to Central Idaho is the marginal risk area. The primary threats are heavy rain, strong winds, and large (but brief) hail.

Some thunderstorms are expected outside this risk area as well, as seen in the UW CAPE (Convective Available Potential Energy) forecast for Saturday evening.

CAPE values will be especially high over Central Oregon, with elevated values continuing through the Washington Cascades into British Columbia. A stray thunderstorm may move through parts of the lowlands, especially the foothills.

What about July 4th? It will be a bit below average, with highs only reaching the upper 60s, as seen in the European model forecast below.

Eastern Washington will be much warmer, with highs in the mid 70s to mid 80s. Fireworks time across the state will be characterized by clearing clouds. The European model sky cover forecast for 11 PM on the Fourth is below.

Most of the lowlands will be clear, with some scattered clouds possible. Most of Eastern WA will be clear as well, with the exception of the SE region and some sections of the central region.

Now…for a critical factor in post-fireworks air quality. Despite a SW breeze across Western Washington during the day, winds will dramatically calm by fireworks time. Peak wind gusts from 11 PM on the Fourth to 5 AM on the 5th are below, forecast by the European model.

With the exception of the Kittitas Valley, most of the state will have calm winds, making it difficult for lingering smoke to clear.

Stay tuned for an update on Sunday.