Northern lights in Washington: tonight’s chance

A storm state, split by the Cascades

Washington's magnetic latitudes are lower than its geographic ones would suggest. The magnetic pole sits over northern Canada, far to the east of the Pacific Northwest, so the whole state is tilted away from it: Seattle at 47.6 degrees north has about the same Kp threshold as Sioux Falls, South Dakota, 4.1 degrees of latitude farther south. In practice, the northern lights in Washington are a storm phenomenon, and the useful forecast is the SWPC watch for G2 or G3 conditions.

Within the state, the north-south difference is modest: from Bellingham to Vancouver the threshold climbs by about 0.8 Kp. The east-west difference in weather is far larger. The Cascades take the moisture out of the Pacific air, and the eastern half of the state sits in their rain shadow. In NASA POWER averages, Spokane's sky in July is at 30% cloud amount, against 47% for Seattle in its clearest month.

Where to stand

West of the mountains, the shores that face north across open water are the best bets near the cities: the north ends of Whidbey and Camano islands, the Skagit flats and the bay at Bellingham. East of the Cascades, the Waterville Plateau, the Okanogan valley and the high ground around Spokane offer wide northern horizons. Wherever you go, the aurora at the edge of Washington's range sits within ten or fifteen degrees of the horizon, so a ridge to the north hides it. The Seattle page and the Spokane page give the dark hours and cloud averages month by month.

The season

Storm timing adds a Pacific twist. The SWPC forecast is written in three-hour blocks of Universal Time, and Washington runs eight hours behind UT in winter and seven in summer, so the block 06 to 09 UT, when storms often peak in the forecast tables, falls between 10 pm and 1 am Pacific standard time, right in the useful part of the night.

Washington keeps some astronomical darkness even in June, unlike Alaska or Scotland, but only about 1.8 hours on the 15th in Seattle. The months with the most clear dark hours are late summer and early autumn, before the Pacific storms set in, which the table below shows for Seattle.