You need 3 things in order to see the Northern Lights: (1) solar activity; (2) darkness; and (3) clear skies.
Unless these three requirements are all present, that “Northern Lights Chasing Tour” you pre-booked months ago simply can’t deliver. This is not to say you shouldn’t try once you get to Iceland! Darkness and clear skies are easy to figure out on your own by simply traveling to Iceland at the appropriate time of year and checking the weather app on your phone. Fortunately, there is also a way for us non-scientist folks to see an “Aurora forecast” by visiting the Icelandic Meteorological Office. Consider renting a car and doing some chasing on your own if the predictions look good. Or, if you really want a tour, wait to book it until you’re actually in Iceland and have an opportunity to check out the necessary forecasts. Of course, if you are booked with a private tour, you'll likely have multiple opportunities to keep chasing those lights night after night.
The Northern Lights are absolutely worth chasing – just be sure to chase them knowing there’s a good chance you’ll catch them.
Happy traveling and Carpe Passportus!
P.S. FUN FACT: Towards the South Pole, this same phenomenon is called the “Aurora Australis.”