Weak La Nina in the forecast: Here’s what it means for ski season in Summit County | SummitDaily.com

Weak La Nina in the forecast: Here’s what it means for ski season in Summit County

A fresh dusting of snow is pictured on the peaks at Arapahoe Basin Ski Area on Monday, Sept. 20. Predictions related to La Nina and El Nino this year offer little insight into Summit County’s upcoming ski season.
Ian Zinner/Arapahoe Basin Ski Area

As the ski season approaches, everyone wants to know how much snow Summit County will get this year.

Joel Gratz, founding meteorologist of Open Snow, explained that at this point in the year, the only way to have some sort of idea about what the upcoming season will look like is to determine whether it will be an El Nino or a La Nina year and then to look at past weather patterns associated with those climate phenomena. El Nino and La Nina refer to warmer or cooler water temperatures, respectively, in the Pacific Ocean and impact weather worldwide.

“The reason people talk about it now is because El Nino and La Nina is the only factor that we can kind of reliably predict many months in advance,” Gratz said. “All the other things that control storm tracks aren’t able to be predicted more than really a week or two in advance, which is when we’re just tracking each individual storm.”

This year, there’s a 70% to 80% chance that La Nina will arrive this winter, and models are showing that La Nina will be weak to moderate.

So what does this mean for our ski season? Unfortunately, not much.

Gratz explained that the stronger the La Nina or El Nino, the better chance Colorado will get at least average snowfall — if not above average. But a weak La Nina means anything could happen.

“La Nina can often mean pretty good snow, but sometimes it doesn’t, and if I were a skier right now, I probably wouldn’t plan anything definitive in Colorado due to the La Nina forecast,” Gratz said. “It’s not a reason to schedule more trips or schedule fewer trips.”

Typically, Gratz said La Nina does well for the Pacific Northwest and northern Rocky Mountains, meaning it’s likely to be wetter than normal in those areas. On the flip side, El Nino often favors the south in terms of precipitation. However, as Colorado is in the middle of North America, correlation between weather and El Nino and La Nina is weaker. Gratz said El Nino often means some bigger storms are seen on the Front Range, but Summit County is often unaffected.

“Many past seasons with a La Nina have done pretty well in the northern mountains where Summit is. Last season was a La Nina, and it was OK but generally below average,” Gratz said.

“I don’t generally use that to get super excited or not excited about the season,” he said. “… I’ve been forecasting now for a little more than 10 years, and I used to get a little bit more excited about seasonal predictability, … and as I’ve done this more and more, I’ve realized that it just doesn’t work very well.”

To complicate things more, Gratz noted that Colorado’s worst season and its best season in the past 30 years both occurred when there was neither a La Nina nor an El Nino. Overall, Gratz said El Nino and La Nina are general concepts that sometimes work at the local level.

While making predictions based on La Nina and El Nino is a fun way to get ready for the ski season, Gratz said that today’s meteorology just isn’t great at long-range predictions and that if you’re planning to ski a certain day, your best bet is to look at the forecast within 10 days.

“The forecast for storms within about a week out — seven to 10 days — that’s pretty reasonable, right? We kind of plan our lives around these storms and potential powder days, but once you go beyond about 10 days and out into these multimonth thresholds, people are definitely dabbling in trying to get better at this, but it is not a spot that meteorology shines in terms of accuracy right now,” Gratz said.

The seven- to 10-days out marker is for when meteorologists have their eye on an incoming storm but don’t have many details, Gratz explained. After that, they’re filling in those details, such as snow accumulation ranges, until the storm hits.

While it’s essentially anyone’s guess what the ski season will look like in terms of powder days, the National Weather Service’s two week forecast isn’t promising. Treste Huse, a senior hydrologist for the National Weather Service, said that through the end of the month, above normal temperatures are expected. She added that there is a high chance that the remainder of September will be dry.

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