Massive solar storm: Seattle, Portland, even N. Calif. may see auroras
Updated 12:06 pm, Thursday, September 7, 2017
Photo: NOAA SPACE WEATHER PREDICTION CENTER
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.)
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."