Northern Lights may be on display tonight in South Sound

The sun has been very active recently and two large solar flares this week have sent coronal mass ejections (CMEs) toward earth.

A coronal mass ejection is a burst of magnetized plasma that interacts with the earth's magnetic field to produce geomagnetic storms and an enhanced aurora around the north and south poles.

The aurora borealis — the "Northern Lights" is a region of charged gases in the ionosphere, a region around 50 miles above the earth's surface. These gases give off light from green to orange to red depending on the type of gas being excited by the charged solar particles.

Most importantly for us in the Pacific Northwest, the interaction of the CME with the ionosphere as the pulse passes earth can mean the visible aurora much farther south than typical.

Will we see the Northern Lights in the Seattle-Tacoma area? It's possible, but we won't be able to say that a visible aurora is likely until about 30 minutes out.

That's when the charged solar particles pass satellites and begin to be detected by ground stations on earth.

An auroral display across Western Washington and the upper reaches of the lower 48 usually just means a faint greenish or reddish glow on the far northern horizon, visible away from city light and clouds.

Tonight's display could be more impressive given the strength of the solar flare and CME, and while we are certain to be cloud-free around Seattle and the Pacific Northwest tonight, the moon is 81% full and rises at around 9:30 p.m. Seattle time and is up all night.

That is not good for auroral viewing during the "prime time" of midnight to 3 a.m.

Still, a vibrant auroral display — if one were to occur tonight — might be impressive even with the interfering moonlight.