A highlight for many wintertime visitors to Alaska is running down a display of northern lights.

But looking for the aurora is always a game of chance -- even nights predicted for good viewing don't always pan out. It needs to be clear. You need to get far from city lights. And, of course, the universe itself has to cooperate, as supercharged particles ejected from the sun interact with the Earth's thermosphere in just the right way to produce celestial light shows when viewed from below.

By the time the sun starts hanging around for 18-20 hours per day, everybody pretty much gives up on northern lights for the season. Which makes the summertime aurora an even more elusive beast. It takes a particularly strong set of magnetic disturbances in Earth's atmosphere to overcome the impediment of long days.

In the winter, many people recommend heading north to get a better glimpse at the northern lights, but the opposite is true during summer. The farther south, the better chance you have of stumbling upon northern lights.

To that end, the University of Alaska Fairbanks Geophysical Institute has created a handy guide for viewing the aurora during the northern summer. For the most part, it means that aurora viewing is going to be "very limited" anywhere north of Anchorage from mid-May until August. You can see the aurora while it's still light out, but not fully light. It has to be closer to dusk, which is more or less out of the question during the peak of Alaska's daylight hours from June through July.

Visitors to Juneau, Alaska's capital city, might have better luck since daylight hours are a little less extreme there in the summer. But that has its own difficulties, notes Dirk Lummerzheim of the University of Alaska Fairbanks Geophysical Institute.

"Seeing it in summer is difficult because the sky is too bright in Alaska," Lummerzheim wrote in an email to Alaska Dispatch. "(Southeast) Alaska would definitely work, but the weather there tends to be too cloudy. And then, of course, we would need a fairly active aurora, so that it does move south."

Like in the winter, seeing the aurora in summer is a crapshoot -- it takes the right blend of conditions and a strong-enough solar storm to precipitate appearance of the aurora at southerly latitudes, farther from the north pole.

The intensity of the northern lights -- and thus the likelihood of being able to see them in the "off season" -- is measured on a kp-index scale that ranges from zero to nine.

"The higher the Kp index, the farther to the south the aurora extends," Lummerzheim wrote. "It also gets brighter. But in Fairbanks, for example, the sky never gets dark enough during the 8-10 weeks surrounding solstice to see even very bright aurora."

The National Oceanic and Atmospheric Administration's Space Weather Prediction Center offers a 3-day kp-index forecast, and the aurora-centric website Soft Serve News has predictions within 10 minutes.

Contact Ben Anderson at ben(at)alaskadispatch.com