Northern lights in Idaho: tonight’s chance

The panhandle and the plain

Idaho runs about seven degrees of latitude from the Nevada line to the Canadian border, and from Sandpoint to Pocatello its towns spread over 4.5 degrees of magnetic latitude. In Kp, that is the difference between a moderate storm and a strong one. The panhandle, wedged between Washington and Montana, shares the thresholds of Spokane and Kalispell: Sandpoint on Lake Pend Oreille needs Kp 5.7. South of the Salmon River country, the Snake River Plain needs a G3 storm almost everywhere.

Dark country

Southern Idaho trades latitude for darkness. Craters of the Moon National Monument and Preserve, on the lava fields between Arco and Carey, was designated an International Dark Sky Park in 2017, as the National Park Service announced, and the mountain valleys of central Idaho around Stanley are among the least lit places in the lower 48. On a storm night those skies make a faint aurora easier to see than from a town that sits a little farther north but under its own glow. Mountain horizons are the catch: in the valleys, the northern sky starts ten or twenty degrees up, which hides the low edge of a display. Open plains and high benches do better than canyon floors.

Two time zones, one storm

Idaho is split between Pacific time in the panhandle and Mountain time in the south, a detail that confuses storm watchers more than it should. The aurora does not care about clocks: a storm that peaks at 05 UT peaks at 9 pm in Sandpoint and 10 pm in Boise during standard time. The tool takes the time zone of the place you type and prints every hour in it, so the best hours it shows for Coeur d'Alene and Idaho Falls on the same night can look an hour apart while describing the same burst of activity.

Seasons and weather

Boise's sky is at its clearest in July, at 26% cloud amount in NASA POWER averages, and cloudiest in December, at 73%, when winter inversions trap low cloud on the plain. The dark hours run from about 3.9 on the 15th of June to 11.6 in mid-December, as the table below shows. Late summer and early autumn combine both, which is why September comes first by clear dark hours. For the panhandle, the Spokane page is the closest match.