Planning a ski vacation well in advance is a tricky proposition. Early birds can’t possibly know what snow conditions will be several months or weeks out. And those who wait for flakes to fall risk missing out on special deals — if there is any availability left at all late in the booking game.

One strategy for early bookers is to consider where the snow has fallen most in the past. The highest snowfall averages over the course of more than 10 years include at Jay Peak in New England, Alta and Snowbird in Utah, and Revelstoke in British Columbia, according to Joel Gratz, the founder of Opensnow.com, which offers snow reports and forecasts by a group of powder-hungry meteorologists. “However, every season is different,” he points out. “And most often, snow forecasts for an entire season are not reliable, so we can’t necessarily use the past as a perfect guide to the future.”

Case in point. If you avoided Colorado this holiday season because of dismal early conditions last year, you sorely missed out. Plentiful snow allowed ski resorts to open early with more terrain than usual. Aspen Snowmass had already received more than 130 inches by the end of December, with more than 5,300 acres of terrain open for skiing, compared with 1,900 the previous year. Vail Mountain’s Back Bowls opened just after Thanksgiving, marking the third time in the last decade that the backside of the mountain has opened so early, and all the resort’s 5,289 skiable acres were open before the New Year. Breckenridge, which reported more than 172 inches by early January, had opened all five of its peaks by Dec. 12 — the earliest all five were open in the resort’s history .

Scientists say climate change will make the booking equation all the more complicated as temperatures continue to rise. The Climate Impact Lab, a group of climate scientists, economists and data analysts from the Rhodium Group, the University of Chicago, Rutgers University and the University of California, Berkeley, released an analysis last year projecting that if trends continue, some popular ski resorts could lose as much as a month of the season within the next two decades.