Ski Lines: Sierra Spring Corn

By Wendy Lautner

“When Sierra Spring Corn is concerned, the early bird gets the corn.”

For this last Ski Lines column of 2009-10, I’d like to leave you with some serious food for thought. Today, we’re going to talk about corn, specifically Sierra Spring Corn.

If you’re a skier, you know what I’m talking about. It’s that soft, smooth layer of buttery snow that gently slides out from underneath your edges on a warm spring day. But how did it come to be called corn in the first place? I decided to explore the similarities between the Sierra Spring Corn that you find on the slopes and the Sweet Corn that you roll in butter and put on your plate.

My dad is a farmer and the pinnacle of his growing season is always the quality of his Sweet Corn at the end of each summer. It’s a crop that takes the entire season to mature. And, as it does, you could say that the story of each summer is stored in its kernels. Was there enough rain? Did the sun shine through the clouds? Did the coons break into the field and destroy the stalks? Did my dad beat the worms to the harvest? All of these questions are answered on the plate.

Like Sweet Corn in the field, true Sierra Spring Corn on the slopes also takes the entire season to mature. Sierra Spring Corn captures the story of each winter in its grains and is re-lived with every sweet, arcing turn on the descent.

So, how is corn on the slopes made? And, how can you time your harvest to beat the worms? To answer these questions, and before you overexert yourself, this week I talked with Snow Hydrologist Randall Osterhuber at the Central Sierra Snow Pack Laboratory on Donner Summit.

Randall’s relationship with the snowpack is intimate. Since the 1980s, he has spent his career measuring its depth, water content, quality, documenting the data and plotting graphs to show relationships between snowfall, snowmelt and the environment.

This Year’s Snowpack
Randall says this year’s snowpack has “toggled right around average in the Sierra Nevada,” as of March 30. For water supply, Randall says “average barely cuts it anymore with all the demands on water like recreation, agriculture, electricity production, riparian health …”

For skiers, an average year means you’ll probably be skiing well into spring and even summer if you’re motivated. Keep in mind, however, the “nature of snow distribution – this year the Tahoe Sierra looks good especially along the West Shore of Lake Tahoe and Donner Summit.” Randall reports a “shallower belt just south of Mammoth with the snowpack getting deeper again around Mount Whitney.” I’ll take that to mean you might want to hit the Convict Lake area sooner than later.

What is Corn
Most skiers know that corn is made through a relatively predictable freeze-thaw cycle. Below-freezing temperatures (generally at night) harden the snow, while above-freezing temperatures (during the day) melt the top couple of inches for ideal corn conditions. Corn snow is at its most basic level, a function of spring. Around this time of year, Randall says the water content in the snowpack is about 30 to 35 percent and about 65 percent air. The contents of powder snow may be 5 percent water and 95 percent air (no wonder we feel like we’re flying). Compare this to an ice cube: 95 percent water and 5 percent air. Corn snow is essentially the happy middle ground between ice and powder.

So, how’s it made? “As you bring snow up to its melt point (at 32 degrees Farenheit) the individual grains get larger. The warmer ones are bigger and they give off heat to the other colder snow crystals,” Randall says. “As the weather gets warmer and snow turns into water, liquid layers percolate through the snow pack and the pore space (air content) decreases.” This process also helps to consolidate the snowpack. While simple to understand, finding great corn snow can still be difficult to predict because “melt index equations have something like 13 different variables,” Randall says. “You can’t talk about a single one of those variables without talking about all the rest, it’s a function of everything together.”

Freeze-thaw basics
One of the most basic variations in the alpine freeze-thaw cycle is aspect. It’s easy to figure that east-facing slopes get morning sun and west-facing slopes get afternoon sun (considering there wasn’t cloud cover at any particular time of the day). South-facing aspects tend to get the most sun and therefore warm up faster and melt off quicker, whereas north-facing slopes can hold cold, winter snow deep into spring.

Temperature is another basic factor. The warmer the day, the faster the melt, right? Not so fast. Yes, warmer temperatures do melt snow faster, but Randall warns against simply glancing at the day-time high. “You might see that the day-time high was 50 degrees,” he says. “But there’s a big difference between 50 degrees for one hour and 50 degrees for 13 hours.” Considering temperature duration will give you more of the whole story.

Angle, in mountain environments, also is a significant factor in corn quality. Randall compares it to getting a sun tan, “A steep, south-facing slope will absorb more heat than a south-facing meadow because the angle of incidence is closer to 90 degrees,” he says. “It’s like sitting upright and facing directly into the sun to get a sun tan, you get more energy input when you’re sitting up than when you’re lying down.” So, on south-facing slopes steep angles might be prone to melt out earlier, but on north-facing slopes the opposite is true.

And then there’s wind, it also can play a role in corn quality, Randall says. “Wind can either add or remove moisture. If the air mass is dry, winds can take moisture away from the snowpack. This is called sublimation when water goes from ice (snow) to vapor without going through the liquid phase. People might ski an area that has a breakable crust one day, but with wind action that crust can be removed. On corn snow, wind can keep the very surface of the snowpack cool during the day so you have less of a melt cycle on those days.”

Re-radiation is another melting factor. Because darker objects re-radiate absorbed heat, snow around darker things tends to melt faster. For this reason, back-country skiers like to keep rocks off the skin track, and while winter routes might snake up through the trees, treed or rocky slopes might melt faster than open bowls due to re-radiation.

One last thing – remember the saying, “the early bird gets the worm?” Well, when Sierra Spring Corn is concerned, the early bird actually beats the worms and gets the corn.

Wendy Lautner is a snowboarder, free heeler and freelance writer. Her first book, “Day & Section Hikes on the Pacific Crest Trail: Northern California,” will be released by Wilderness Press in May.