When I was just cutting my teeth as a mountain meteorologist in Colorado, a far more experienced forecaster fed me a statistic that I’ll never forget. He said that more than half of all precipitation in the mountain west comes in less than 20 percent of the days. Said another way, just a few big storms are responsible for the majority of yearly snow and rain in the western U.S.

This has massive implications for meteorologists, water managers, and of course, skiers and riders who love powder. It’s fun to get out on the slopes as much as possible but if you have limited time and want to make the most of the powder, honing your snow search to find the few big storms can make your season.

Between March 11 and March 21, 2012, some areas along the west coast received nearly 100 inches of snow. Think of this stretch of days as one of those 20 percent periods, when the vast majority of snow falls. The series of storms that brought these deep accumulations also brought happiness to many powder seekers, especially in the Tahoe area that had a very dry season up until this cycle.

To get a feel for how much impact just one week can have, let’s look at maps of snowpack across the west. These maps are broken up into river basins and use SNOTEL stations to gauge how much snow is actually on the ground. SNOTEL stations are remote backcountry weather stations set up from the 1960s to 1980s with the primary intent to measure snow so that water managers could predict the amount of runoff during the spring and early summer.

This first map is from Sunday, March 11, just before the big snows started up. The numbers show the percent of average snowpack in each river basin. Notice lots of 90s in Washington, 80s and 70s in Oregon, 80s and 90s in Idaho, and 40s in the Tahoe region of California and Nevada. These numbers all point out that the snowpack was below normal. 

2012-03-11

But look at the map on March 21, just 10 days later. Washington is now mostly over 100 percent of average, Oregon jumped about 10 percentage points into the 80s and 90s and Idaho jumped 10 to 15 percent with numbers now into the 90s and some over 100 percent. Tahoe rose 14 percent and is now close to two-thirds of average, a remarkable jump from the 49 percent of average that was recorded just before this series of storms.

2012-03-21

Here’s another thing I remember from the experienced mountain forecaster I met years ago. He said that there’s really no such thing as average in the mountain west. Rather “average” weather is just a 30-year compilation of extreme storms. And looking at the snowfall over the last 10 days, this seems about right. Rarely will we ever see “average” conditions in big mountains, and instead the skies will either be sunny and bluebird or dumping lots of snow. Luckily for the west coast, this series of storms increased the snow pack by 10 to 15 percent in what seemed like just a blink of an eye. And that’s how the west was won.

Meteorologist Joel Gratz is the creator of opensnow.com and is based in Boulder, Colo.