Two things are necessary to see the Northern Lights:
Clear weather and atmospheric activity.
The University of Alaska offers this prediction information. And for the picture in Iceland, I used the website for Aurora Forecasts. On that evening, the forecast looked like this:
So the green means the probability of Aurora activity, and the skies were clear.
On the evening this was shot, the skies were clear enough to take this 30 second exposure. It appeard silver to us on the ground but the photo shows green!
So what will be the chance tonight? Check out NOAA.