The secrets of snow science
January 15, 2018
FRISCO, Colo. – Meteorologist Joel Gratz can remember his best powder days perfectly. Just as vivid are memories of the ones he missed thanks to a bad forecast.
When Gratz first moved to Colorado in the early 2000s, plenty of his forecasts were way off, predicting dustings before big dumps or hyping up storms that ended up being duds.
"Nothing teaches you better than when you tell all of your friends to go ski somewhere because there's going to be a foot of snow and there ends up being an inch," he told a packed audience in Frisco Wednesday night. "They make fun of you for the rest of the weekend. That is good motivation to go back, figure out what went wrong, and not let that happen again."
In his spare time, Gratz got to work figuring out the vagaries of snowstorms in the High Country, which can be underestimated or undetected by far-away radar towers blocked by the mountains.
Nothing teaches you better than when you tell all of your friends to go ski somewhere because there’s going to be a foot of snow and there ends up being an inch.”Joel GratzMeteorologist, founder of OpenSnow
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By 2007, he was confident enough to send forecasting emails to a group of 37 friends. The network snowballed largely by word of mouth on chairlifts, and several years later Gratz quit his job and started what is now OpenSnow.com, a go-to site for powderhounds across the country. More than 2.2 million people now visit it each season.
At least 100 of those followers were present Wednesday night at the Frisco Adventure Park Day Lodge for the aptly named "Pray for Snow" party and snow science talk, sponsored by the town of Frisco and ELEVATE co-working space.
"I do the majority of my work at 5 a.m. sitting in front of my computer in a dark room or on the floor of friends' houses where I'm staying," Gratz said. "So I know that you're all out there, but it's super cool to actually see you."
The evening brought some relief for skiers and riders wringing their hands over this winter's lackluster snow totals — and not just because several inches of fresh were falling outside.
"We're just below average in Summit County (Colorado), but not that far below — maybe one storm below," Gratz said. "We're actually kind of similar to where we were last year, which is really hard to believe because it doesn't feel that way."
Statewide, snowpack is roughly 50 percent of what it typically is this time of year. But the north and northeast mountains are faring relatively well, between 70 and 80 percent of the year-to-date average since the 1970s.
The sporadic snowfall predicted in Summit County through Friday will certainly help, but it's not the big wallop needed for snow totals to get back on track. Moisture building up over the Pacific Ocean, however, indicates that a big storm could come next weekend.
"I don't know what's going to happen next week, but next Friday and Saturday should be a pretty darn good storm," Gratz said. "I'm optimistic and excited for the last two weeks of the month."
Gratz is one of few meteorologists who can elicit "oohs" and "aahs" during a Powerpoint presentation. An avid powder skier himself, he's also one of the few who would include a slide titled "Blower Pow." (The key to that extra-fluffy snow? Big snowflakes that lay down with plenty of air in between them).
Predicting how much snow a storm will drop in the mountains is a tricky business. Gratz has become one of the best by trial-and-error, figuring out which wind directions are likely to bring the biggest totals.
"Different wind directions favor different mountains," he explained, displaying his cheat sheet of favorable wind directions for each of Colorado's ski areas. "In Summit, our best wind direction is northwest-ish, however there's a trick I found last year after being wrong a couple of times."
West-southwest winds, he explained, usually bring dull storms in Summit. But when the storm is warm and moist, the high elevation peaks in the area tend to do unusually well.
The interactions between wind and mountains, known as orographics, are some of the most important factors for predicting snowfall; if you get those right, Gratz said, your forecast will be in the right ballpark about 70 percent of the time.
"If you want to have an epic powder day at Vail, it's going to happen on a northwest wind, 99 times out of 100," he said. "The wind kind of gets funneled into the Gores and then gets pushed back — it's almost like a fire hydrant effect."
Wind direction is a useful guide for layman forecasters, but truly understanding mountain snowfall requires literacy in a host of meteorological concepts. Even that isn't always enough, as Gratz readily admitted. Some weather events happen on such a minute scale they are almost impossible to observe.
A prime example is what Gratz calls the "Steamboat surprise," when a small storm unexpectedly dumps several feet of snow on Steamboat Ski Resort.
"That's actually the precipitating factor that got me to start making my own forecasts, because I missed a quote, 'booty-deep day' in November 2005 where they got 48 inches in 48 hours, and I was so mad I was like, OK, I'm going to figure this out," he said.
After years of study, Gratz has come to close to unlocking the secret. According to his observations, the Steamboat Surprise happens when a storm comes on a west-northwest wind and the mountaintop temperature is five degrees.
"The trick is that every time you get a wind from the west-northwest and a temperature of five degrees, you don't always get the Steamboat Surprise," he said. "So there's other stuff at play that's probably operating on such a fine scale that the weather models might not pick up on it."
If predicting weather is hard, though, predicting climate trends is even harder. While temperature data show a clear upward trend of about 4 degrees in the Dillon area over the past century, there's no clear trend for precipitation levels.
"Here's what we know: temperatures have increased and they will likely continue to increase," he said. "Precipitation, there's no trend and no confidence in a trend. So you combine those, warmer temperatures and the same precipitation, potentially that means more rain than snow at lower elevations, and potentially that means more drought conditions."