Northern lights tonight: yes, maybe or no for your town

Kp is one number for the whole planet. SWPC derives it from magnetometers between 44 and 60 degrees of magnetic latitude, and a high value means the ring of aurora around the magnetic pole has grown and slid toward the equator. What a forecast of Kp 5 means for you depends entirely on how far your town sits from that ring, and the ring is centred on the magnetic pole in northern Canada, not on the geographic pole. That is why Seattle, at 47.6 degrees north, needs about 6.4 while Minneapolis, 2.7 degrees further south, needs only 5.9: Minneapolis is closer to the magnetic pole.

This site gives every place its AACGM-v2 magnetic latitude, the coordinate system the OVATION model itself uses, computed for October 2026 at an altitude of 110 km where the aurora glows. Then it applies two published relationships. Up to Kp 5, SWPC's rule: the southern edge of the oval sits at 66 degrees magnetic latitude at Kp 0 and moves 2 degrees toward the equator per step. For the big storms, the latitudes the NOAA storm scale gives for where aurora has been seen: 55 degrees at G2, 50 at G3, 45 at G4, 40 at G5. At each Kp the site keeps the more southern of the two lines, which is the oval rule up to about Kp 6.3 and the storm scale beyond. The Kp index page shows both lines for any town.

A faint display needs a black sky, and the sky is not black at sunset. The tool computes, for your coordinates and the night you pick, the moment the Sun's centre drops 18 degrees below the horizon and the moment it climbs back. Between those two times the sky is as dark as it gets. Hours with the Sun between 12 and 18 degrees down count as twilight: a bright storm can still show, so the answer can reach maybe, never yes.

This matters most where aurora is easiest. Fairbanks has no astronomical darkness at all in April, May, June, July and August, and Edinburgh none in May, June and July. A Kp 7 storm in late June is invisible from places where it would be overhead in March. The dark sky hours tool lists the dark window for the next thirty nights anywhere.

Most aurora pages stop at Kp. Yet on a G3 night the deciding question for most people is whether the sky will be clear, and that comes from a weather forecast, not a space weather one. For places in the United States the tool reads the hourly sky cover of the National Weather Service gridpoint that contains your coordinates. For Canada, the United Kingdom and as a fallback, it reads the cloud fraction of the Norwegian Meteorological Institute's Locationforecast. Each hour is rated clear at 30% cover or less, broken up to 70%, and overcast above. You can override the forecast with what you see out of the window.

For each hour, the tool compares the Kp forecast for that three-hour block with the Kp your place needs. At or above it, activity is strong; up to 1 below it, activity is at the edge; lower, it is quiet. If the current OVATION run puts a 10% chance of aurora within 500 km of you, the hour that is happening now counts as strong whatever the Kp says. The hour's answer is the weaker of activity and sky: yes needs strong activity, a clear sky and full darkness; maybe is any mix of edge activity, broken cloud or twilight; no is quiet activity, overcast or daylight. A Moon more than 75% lit and more than 10 degrees up turns a narrow yes into a maybe, because it hides faint aurora without changing it. The night takes its best hourly answer, and the best time is the longest run of hours that reach it.

These thresholds are this site's own rules, written on the method page so that you can disagree with them. None of them is an official NOAA verdict: SWPC forecasts space weather, not your backyard.

A yes is a reason to go out, not a guarantee. Kp forecasts made a day ahead often miss the timing of a coronal mass ejection by several hours, and a storm can fizzle when the magnetic field it carries points north. The OVATION line is the most reliable short-term signal because it is driven by the solar wind measured about 1.6 million km upstream, which gives 30 to 90 minutes of warning. Reload the page during the night: the feeds refresh, and the answer for the current hour updates with them.

Go north of the city lights, face north with an open horizon, and give your eyes twenty minutes. At the edge of visibility, the aurora often looks like a pale grey arch that a phone camera turns green; the phone photography guide gives the settings. SWPC's own advice puts the most active hours 10 pm to 2 am local time, and the hour strip of the tool shows which of those hours your sky will cooperate in.

The first results for this search give a planetary Kp, a map of the whole pole or probabilities by latitude band, and leave the reader to work out what they mean at home. This page does the opposite: one place, one night, one answer with its hours, and every rule written down. Kp and OVATION come from the public JSON services of the NOAA Space Weather Prediction Center, read by your browser directly. Sky cover comes from api.weather.gov or api.met.no, also read by your browser, with your coordinates rounded. Darkness and the Moon come from astronomical equations run on your device and tested against the JPL DE421 ephemeris. Magnetic latitudes come from the AACGM-v2 model, monthly cloud averages from NASA POWER, and town and ZIP code positions from the Census Bureau's 2024 Gazetteer. Nothing you type is sent to us.