Massive solar storm: Seattle, Portland, even N. Calif. may see auroras

JAKE ELLISON, SPECIAL TO SEATTLEPI.COM

Updated 12:06 pm, Thursday, September 7, 2017

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Photo: NOAA SPACE WEATHER PREDICTION CENTER

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Two large sunspot groups visible on the disk of the sun Sept. 5, 2017. 

The beautiful thing about a solar flare that ruptures a filament of the sun's magnetic field and fires plasma into space — a coronal mass ejection — is that when it hits Earth, we get expanded northern lights or aurora. If the ejection is big enough, and hits the Earth just right, you can spot aurora much farther south than usual.
The current plasma burst from the sun stems from an M5 or relatively medium-strength flare on Monday. The flare's geomagnetic storm, the space weather version of a small hurricane, is projected to arrive late Wednesday, according to NOAA's Space Weather Prediction Center. (Note that space weather changes and so the agency's predictions will evolve as the week goes on.)

The outer range of visibility for the resulting aurora could stretch south over Washington, Oregon and as far as the tip of Northern California. (There's a map in gallery above.)
NOAA provides a very informative caveat to its projections: "This probability forecast is based on current solar wind conditions measured at L1, but using a fixed 30-minute delay time between L1 and Earth. A 30-minute delay corresponds to approximately 800 km/s solar wind speed as might be encountered during geomagnetic storming conditions. In reality, delay times vary from less than 30 minutes to an hour or so for average solar wind conditions."