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Earth's skies may dance in auroral green St. Patrick's Day

I've got green on my mind and it's not because I'm Irish. On March 15 a magnetic filament - a strand of solar flame silhouetted...

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A solar flare in the early morning hours of March 15 CDT sent a cloud of high-speed subatomic particles called a coronal mass ejection toward the Earth. It's expected to arrive overnight tonight through Sunday. A disk blocks the sun in this photo taken with the Solar and Heliospheric Observatory (SOHO), allowing a better view of the cloud. Credit: NASA / ESA

I've got green on my mind and it's not because I'm Irish. On March 15 a magnetic filament - a strand of solar flame silhouetted against the sun's brilliant disk - erupted in a long-duration flare that sent a blast of solar plasma directly toward the Earth. Traveling at 2 million miles per hour, the cloud of high-speed electrons and protons will slam up against our planet's magnetic bubble and possibly touch off an auroral storm.

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Auroral display over Duluth Oct. 8, 2012. The green color, the most common seen in northern lights, is caused by oxygen atoms in our atmosphere energized by high-speed electrons from the sun. When the atoms return to the "unexcited" state, each releases a bit of green light. Photo: Bob King

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Minor auroras are forecast for mid-northern latitudes tonight March 16 with a chance for a major storm on Sunday. If you live in the Arctic, get ready for a good show - chances for a major to severe storm stand at 70% Sunday (20% for mid-latitudes).

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Wide-field view of the same coronal mass ejection taken by SOHO around 3 a.m. CDT March 15. Venus is to the lower right of the sun. Credit: NASA / ESA

These are the best numbers I've seen in some time, so be on the lookout this weekend for green rays step-dancing across the northern sky.

As always, keep an eye on the Kp index   and the extent of the auroral oval , both of which are useful indicators of auroral activity. If the Kp index bar is colored red (equal to 5 or more), there's a good chance auroras are out at least for the northern U.S. and southern Canada.

As I write this in the wee hours of Saturday morning, the index is already rising and auroras appear to be pushing into the far northern U.S. If it wasn't for a heavy snow falling, I'd go out for a look-see right now. More updates later today.

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