How to read tonight's aurora forecast
The Tonight screen answers one question: what are the odds that you see the northern lights with your own eyes tonight, from this spot. Here is what every part of it means.
The big number
The percentage is the chance that someone standing outside here sees the aurora during the best hour still to come tonight. It is not a chance for the whole night, and it is not a camera's chance, which is always higher.
The lines under it fill in the rest. Right now gives the chance at this moment, and when the best hour comes. Clear sky would make this 78% shows what cloud is costing you. Adjusted against field reports means the number has been checked against what people at this latitude actually saw on similar nights.
The verdict
The word above the number is a band of it, so you can read the night at a glance.
| Verdict | Chance |
|---|---|
| Excellent | 70% and up |
| Good | 45 to 69% |
| Possible | 20 to 44% |
| Unlikely | under 20% |
Below threshold is different. It means the sun's activity is too low to reach this latitude tonight, whatever the sky does.
The four bars
Under the number, four bars show what the forecast is made of, at the best hour left tonight.
- Activity: the current Kp against the minimum Kp this place needs (Whitehorse needs about 1.3), plus what the solar wind's Bz is doing.
- Darkness: how far below the horizon the sun is. Twilight washes out faint aurora.
- Cloud: how much of the sky is covered, averaged from four weather models.
- Moon: how full and how high it is. A moon below the horizon costs nothing.
The bar marked Limiting factor is the one holding the number down. Tap What do these numbers mean? for a short definition of each term.
Hour by hour (Pro)
Pro adds Tonight, hour by hour: one bar for every dark hour. The solid bar is the chance with tonight's cloud, and the faint bar behind it is the chance under a clear sky. Below it, Moon tonight shows the phase, rise and set. When NOAA's odds of a solar flare are raised, a flare warning appears here too. Free shows the first two hours.
The next five nights
Further down, The next five nights helps you plan. The first three nights each get a chance, a verdict, the hours of darkness, the moon, the Kp forecast and the cloud at the best hour. Nights four and five show darkness and moon only, marked Outlook only, because a cloud forecast that far out is not worth trusting. A line underneath names the best of the five.
Changing location
Tap the place name at the top, or the Locations tab, to switch. You can search our destinations or tap Use my current location for a forecast wherever you are. To keep a place that is not on the list, tap Save as my aurora spot. Every device gets one saved spot, free, and it stays pinned at the top of your list.
