Forecast transparency
How the northern lights forecast works
Northern Lights Tonight turns scientific space-weather data into a location-based signal for a practical question: is this night worth watching from here?
01
Aurora activity now
The current rating begins with the latest NOAA OVATION aurora grid. We inspect the modeled aurora activity at and north of each location, with an adjustment based on hemispheric power.
02
Nightly Kp forecast
The short outlook uses NOAA’s three-day planetary Kp forecast. We compare the strongest value in each viewing window with NOAA’s approximate auroral-oval boundary of 66° magnetic latitude minus about 2° per Kp level.
03
Darkness window
Each outlook uses the city’s local viewing window while the Sun is at least 6° below the horizon. The forecast also labels whether the darkest point reaches nautical twilight, astronomical twilight, or full astronomical darkness, so limited summer contrast is not mistaken for full darkness.
04
Local interpretation
A location just south of the estimated oval can receive a low horizon-viewing signal. The site converts that distance into four practical levels: none, low, medium, and high—not statistically calibrated percentages.
What the forecast does not include
Weather data can describe broad cloud conditions, but it cannot account for street-level light pollution, terrain, buildings, or a cloud bank that differs from the model. A high aurora rating can therefore still produce no visible result from a particular viewing spot.
Data sources and timing
- NOAA Space Weather Prediction Center OVATION model for the current aurora grid.
- NOAA three-day forecast for expected planetary Kp activity.
- NOAA aurora viewing guidance for the approximate relationship between Kp and magnetic latitude.
- The website refreshes its city pages every ten minutes when upstream data is available.
Use the rating as a signal, not a guarantee
Aurora can brighten, move, or fade faster than a long-range forecast can capture. The closer you are to the viewing time, the more useful the current model becomes. When a forecast looks promising, use the darkest available part of the viewing window, find a clear sky, and move away from direct light.