Northern lights possible tonight in dark skies near the mountains

The sun launched three plumes of charged particles Tuesday and Wednesday that are forecast to combine and bombard Earth's outer atmosphere today and tonight. That could trigger displays of aurora, or the northern lights, particularly across the northern United States.

If the solar storm is intense enough and peaks at night, the aurora may be visible in parts of the DC area, especially away from light pollution. Usually, that means rural locations toward the mountains, where skies are darkest.

The particle plumes, known as coronal mass ejections (CMEs), were not all directed at Earth, making the forecast complex, according to the National Oceanic and Atmospheric Administration. Moreover, the arrival time of the solar storm is uncertain.

NOAA predicts the storm will peak at level 3 (strong) on a scale of 1 to 5.

"During similar storms in the past, naked-eye auroras have been visible in more than 25 U.S. states," SpaceWeather.com writes.

When there's a chance of northern lights in the DC area, we monitor the Kp index (and proxy indices like it), a measure of a solar storm's intensity.

• If the index reaches 7, the northern lights can often be photographed in rural areas, especially toward the mountains, but are usually difficult to see with the naked eye. (Camera lenses are more sensitive to the colors of aurora than our eyes.)
• If it reaches 8, the lights can often be seen faintly with the naked eye under dark skies near the mountains.
• If it reaches 9, the lights can typically be seen easily with the naked eye under dark skies and photographed even inside the Beltway amid city lights.
• If it reaches 10, the lights can often be seen easily from most locations.

NOAA's prediction is for a peak of 7 tonight, although reality could be different by a point of two.

If the northern lights become visibile in parts of the area, we'll post updates.