My friend Jill has 10 snowboards. Is this excessive? Perhaps not, after all there are well more than 10 different types of snow conditions, so why wouldn’t she have a snowboard for every snowccasion? There’s the split-board for early and late season touring, the split-board for mid-season touring, three park boards (one super soft, one with traditional camber, one with rocker tip and tail), and a few freeride boards for various conditions. Jill and 623 of my other friends moved to Utah to ski because they know that the snow conditions here are not just good, they’re the best.
But why, exactly, is Utah’s snow so perfect, so light, so dreamy and what qualifies as a deep-pow day? To get the answer I went to Dr. Jim Steenburgh, University of Utah’s Atmospheric Science Department Chair and the foremost expert on orographic and lake-effect precipitation, front-mountain interactions, and weather analysis/forecasting.
Nerd alert: Sciency info ahead!
According to Steenburgh, “A deep-pow day is defined as a day when at least 25 cm of new snow falls, with 25 cm representing a subjective minimum threshold at which ski flotation begins. Alta observed 453 deep-pow days during 26 ski seasons of study (November– April). This is an average of 17.4 per season, or about one every 10 days. Although the overall mean water content of snow at Alta is 8.4%, on deep-pow days it’s 7.7%.”
I made up this neato mathematical equation to make sense of the factors involved. I’m no atmospheric scientist, but I think it’s pretty clever.
Low Water Content + Right-Side Up x (Frequency + Storm Size) / Location +/- ~ Lake Effect + ~La Niña = Utah’s Awesome Blower Pow!
Water Content: The lower the percentage of water to snow, the fluffier it is. Water content statistics are based on snowfall and snow water equivalent (SWE) measurements on days with more than three cm of new snow. Measuring snow, however, is incredibly difficult, especially on windy days. The Alta Snow Safety Staff at the Collins Weather Station has a reputation for reliability so many weatherists rely on them to provide accurate data for temperature, wind and other atmospheric conditions critical for assessing snowpack stability and water content in the snow. At Alta, the mean and median water content are 8.4% and 7.6%, respectively. Mean water content is highest in November and April. During the heart of the ski season (December–March), the mean and median water content are 8.2% and 7.5%, respectively.
Right-side up snow: Snowflakes have a top and bottom? In fact, some do, but most dendritic snow crystals are radial symmetric (like the kind you made out of folded paper when you were a kid), but really it’s about the snowfall, not so much about the snowflakes. If the white stuff falling from the sky comes in right-side up, it means the water content of the new snow decreases with time. When storms have “upside-down” snow, the water content of the snow increases with time and that makes for heavy, un-fun, ski-sinking powder. Storms following cold fronts have better chances of right-side up snow than storms following high pressure or warm fronts, which produce upside-down or inverted snow. It depends on whether the temperature increasing or decreasing. If the mercury is rising, we will get upside-down snow; if it’s dropping the snow will be right-side up.
Frequency: We get a lot of high-quality snow in abundance for several reasons. (1) Most storms are not completely depleted after crossing the Cascades, Sierra, and other upstream ranges, (2) the Wasatch gets snow from storms following a number of storm tracks, (3) the Wasatch Mountains are a very large, steep barrier, especially around the Cottonwoods where the terrain rises more than 6,000 vertical feet from the valley floor, (4) the configuration of the topography around the Cottonwoods enables that area to get snow from a variety of flow directions, (5) lake-effect, which is not as important as many people think, but still contributes something, (6) above 8,500 feet, nearly all the precipitation we get in winter falls as snow.
Storm Size and Location: There is no common denominator for big storms. The beauty of Big and Little Cottonwood Canyons is that they get snow from many different storm types. Season pass-holders for ski areas in Big and Little may chide pass-holders of the resorts near Park City because they get comparatively less precipitation as the snow falls downstream. “Big and Little get more snow most of the time because they are on the windward side of the Wasatch Crest and are surrounded by higher topography. Big storms in other parts of the range can be a bit more flow dependent. For example, resorts like Snowbasin and Sundance see their biggest dumps in southwesterly flow,” says Steenburgh. The Canyons snowfall total for the 2010-2011 season was 355,” whereas Solitude reported 624” opening day to closing day and Snowbird reported a record-breaking 783” during a 202-day season that ended on the Fourth of July.
Lake-effect snow: The Wasatch Mountains also have the added bonus of sporadic lake-effect snow. Lake-effect snow occurs when a strong, cold northwesterly wind blows across the Great Salt Lake into a convergence zone, which channels the cold air over the center of The Lake, enhancing precipitation. The high salt content in the water prevents it from freezing, but also reduces the saturation vapor pressure and latent heat flux into the overlying air. Minimal amounts of moisture and latent heat are added to the air and The Lake acts as a lifting mechanism and atmospheric destabilizer, which encourages convection.
We have an average of about 11 events with lake-effect snow each year. A few of these occur before the resorts open. Overall, lake-effect contributes less than 10% of the total snowfall in the Wasatch Mountains and only happens September through May. On the very rare days that we have a big storm with high accumulations of lake-effect snow followed by a morning of clear blue skies and sunshine—well, that’s just a gift from God.
“The best-case scenario for a blue bird day,” according to local weatherman, Brett Benson, “is when a storm begins during the morning hours and continues until the early afternoon. Then a cold Northwesterly wind sets up lake-effect snow Southeast of the Great Salt Lake, which continues into the night and deposits another foot or more (mostly in the Cottonwood Canyons). Ideally the snow stops in the overnight hours and colder air moves in (which is more dense than warm air, meaning it will sink and help lead to clearing skies). The next morning–sunny, blue skies, cold temperatures and a lot of new snow!”
Forecasting lake-effect snow, however, is a major challenge because of its unpredictability and the several factors involved in order to brew it. Mountain weather gurus have developed a keen system to determine the likelihood of lake-effect snow. A few of the factors are: (1) a strong Northwesterly flow that maximizes precipitation for the Salt Lake Valley, (2) a large difference between lake/land temperature favors over-lake convergence, (3) lake-effect is typically initiated during the night when land/breeze convergence is favored and convection occurs predominantly over the lake, (4) limited amounts of directional and vertical wind shear. After the storm is done getting spiced-up by the Great Salt Lake, it travels over the Wasatch Mountains and proceeds to dump mass quantities of the most gnarific snow known to man.
If La Niña makes a comeback this year, we could get so much snow that Jill will have to buy an 11th device to slide around on and possibly a second ski rack to hold all of them. During the epic winter of 2010-2011, face shots all-season long were brought to you courtesy of La Niña and the latest information from the Climate Prediction Center shows we’re setting up to welcome a double-dip La Niña this winter, though there’s no 100% guarantee. La Niña does not favor the Wasatch, but last year was a big year for Utah. Other La Niña years have produced below-average snowfalls.
Steenburgh describes La Niña as “a natural phenomenon that occurs in the central and/or eastern tropical Pacific during periods of enhanced easterly surface winds, which cause cooler waters from the deep ocean to be transported to the surface. It affects the distribution of thunderstorms in the tropical Pacific, which, in turn, affects the storm track at higher latitudes.” And noted, “We can’t reliably predict how much snow will fall even when it is a La Niña year.” Northwestern and Southwestern regions of the United States experience wetter and colder than normal winters, while some Southeast regions have warmer, drier winters. El Niño years are more common and are characterized by unusually warm temperatures in the Northwestern and Southwestern United States. So, in theory, we can expect 200 inches of snow above seasonal averages. The previous three La Niñas (2000-2001, 2007-2008 & 2010-2011) have brought snowfall totals to the 700 inch range in the Wasatch. La Niña more strongly influences the Pacific Northwest and Southwest Canada, loading the dice for above average snowfall in those areas, but their snow is…different.
While watching the weather reports, if you hear the words, “Winter Storm Warning for the Mountains of Northern Utah” or “Lake-Effect,” you may want to call into work sick. Start waxing your skis, snowboards, mono-skis (?) or whatever your preferred snow-slaying apparatus, because that usually means at least a foot of the greatest snow on earth is coming.
For more information about the weather and climate of the Wasatch
Front and Mountains, western United States, and beyond, check out
Tracking La Nina
If you follow weather and weather patterns, as most outdoor enthusiasts do- but perhaps not as much as those who enjoy sliding on snow, you’ve undoubtedly heard of the phenomena of La Nina and El Nino. But what are the origins, and as few skiers and snowboarders have ventured- the cause?
Both weather patterns can certainly affect Utah, and broad swaths of North America, but the origin of the pattern originates in the equatorial Pacific. The Pacific Ocean, between South America and Australia can have a profound effect on our local weather. According to the Utah Climate Center at Utah State University, La Nina describes a situation in which the eastern portion of the equatorial Pacific is cooler than normal. The opposite situation, in which the eastern equatorial Pacific is warmer than normal, has another name —El Nino. Together, El Nino and La Nina form what is known to climate scientists as the El Nino Southern Oscillation, or ENSO.
Martin Schroeder, Staff Meteorologist at the Climate Center explains, “La Nina continues to be a hot topic as, what is presently, a weak La Nina continues to develop in the western Pacific. While temperature and precipitation in many parts of the country have a high correlation to the ENSO index, Utah (especially northern Utah) has a relatively low correlation to ENSO, although it is still somewhat positive.”
Not surprisingly, there are several layers of complexity to such an influential natural phenomenon, sea surface temperatures (SST) are only a part of the puzzle. Another important piece is atmospheric pressure- specifically, the difference in pressure between the tropical western Pacific and the tropical eastern Pacific. Typically, the warm oceanic phase in the east accompanies high pressure in the west, and vice versa. Further, this shift, from one condition- or mode- to another, is periodic, taking 5-7 years to complete a cycle. It is this regular cyclic behavior that makes monitoring ENSO so useful to our ability to project seasonal trends. Not all La Ninas are created equal; some are stronger, some weaker, some last for several years, some for only a few months. Playing a role in which it will be include winds, air temperature and cloud cover. (Utah Climate Update, Issue 36, October 2011).
Generally speaking, La Nina means a cooler and wetter year for the west, while El Nino can lead to drier and warmer years. While big snow years like 1983-84 and 2010 are accepted as big La Nina years, and continuing through 2011-12, Schroeder cautions “it’s best not to label each individual year as either definitively El Nino or La Nina as transition between phases doesn’t align with our calendars. Recent articles are using these data to get people pumped up for the coming ski season. While this is what winter enthusiasts want to hear, it should be noted that nothing is definitive. La Nina often occurs over multiple years with few extreme snowfall years occurring back to back. That being said, even without an extreme event such as last season’s snow fall, an average year in the Wasatch is still pretty good.”
For more information on tracking weather trends and all else Utah weather, go to http://climate.usurf.usu.edu/. NOAA’s Climate Prediction Center (http://www.cpc.ncep.noaa.gov/) also offers a monthly and seasonal forecast for temperature and precipitation.