How to read tonight's forecast

The number that matters is the Kp index, a 0 to 9 scale of how worked up the Earth's magnetic field is. The higher it climbs, the further south the aurora reaches and the brighter it burns. From Iceland you want Kp 3 or above. Hit that on a clear, dark night and you are in business. Sit below it and the lights get shy.

Green is worth the hunt. Amber means things are picking up. Red is a proper geomagnetic storm, the kind of night people book flights around. When the bars up top turn green or brighter, pay attention.
The best time to see the northern lights in Iceland

The season runs from late August to mid April, once the nights finally get dark enough to matter. The sweet spot sits roughly between 9pm and 2am, well away from city glow. Late September and March tend to serve up the most active skies, though the aurora keeps its own schedule and rarely bothers reading the calendar.
A forecast is only half the story

A big Kp number is useless under a blanket of cloud. The real trick is knowing which patch of sky will clear, and being standing under it when it does, rather than parked in a lay-by with sixty other people staring at the same grey ceiling. That part is our job. We watch the same forecast you are reading now, then chase the gaps in the weather to put you beneath the darkest, clearest sky we can find.

Check the numbers above. When they start looking promising, we will handle the driving.