Colorado has seen an ‘unprecedented’ avalanche onslaught this March

(Hugh Carey | Summit Daily News via AP) Colorado Department of Transportation officials discuss with each other near Interstate 70 during a snowstorm, Thursday, March 7, 2019, at Loveland Pass, Colo. Historic avalanche danger caused havoc in the Colorado mountains Thursday, shutting down portions of two highways and prompting a rare warning for drivers to avoid a route leading to some of the state's busiest ski resorts.

Since the beginning of March, Colorado has been dealing with what has been called an “historic and unprecedented” series of avalanches. As much as 100 inches of snow fell in spots during the beginning of the month, and it has led to more than 550 avalanches across the state.

At least eight people have died in avalanches there so far this winter, with the most recent this past weekend when a slide occurred near Crested Butte. The death toll is already above the full-winter average.

Avalanches have also buried roadways, including major ones such as Interstate 70. The threat was enough for the Colorado Department of Transportation to advise not traveling to the mountains for a time.

Other massive snow slides have destroyed woodlands untouched by avalanches for as long as anyone can remember. One near Aspen, more than a mile wide, knocked over as many as thousands of old-growth trees over the weekend. Then, thanks to its great heft and speed, it rushed uphill at the opposite side of a valley.

The region has already surpassed the average number of avalanches for an entire season, and prime time for them is just beginning.

Given the state's high-elevation and numerous mountains, avalanches are no rarity in Colorado. An average of 2,500 happen annually. However, picking up more than 20 percent of the winter average in 10 days is indeed quite unusual.

Ethan Greene of the Colorado Avalanche Information Center described the recent spate of snow slides as a "perfect storm" in an interview with The Coloradoan out of Fort Collins. "[W]e are seeing them in seven of our [10] zones and that has never happened," he noted.

The Coloradoan explained early season snow established a "fragile base" before snow in January and February stabilized the slopes. But, when the early season base eroded as snow piled up in early March, the snow released and "released big," it said.

The supercharged snowfall pattern in early March has largely resulted from a persistent area of low pressure stretching from the West Coast through the northern tier of the United States which has incited storminess.

Meanwhile, a speedy and persistent jet stream pattern has allowed numerous storm systems to traverse the Rockies. Some places picked up as much as 100 inches of snow in the first week of March alone.

And there's probably more to come.

Already, a major storm is taking shape in the Plains Tuesday. It will bring blizzard conditions to eastern portions of Colorado, and new snow throughout much of the mountains.

Due to the expectation of more snow, a fresh avalanche warning has been hoisted for the Sangre de Cristo Range today through Thursday, while watches remain in effect elsewhere. "Very dangerous avalanche conditions exist. The avalanche danger is high(Level 4 of 5). Very large avalanches are likely," the warning stated.

While additional avalanches are a good bet in the near term, the fact is that these slides are complex events which come down to small-scale features. As such, forecasting them deep into the future is difficult. There are still some hints to what we might expect.

"Avalanches are much more common in spring everywhere," Brian Brettschneider, a climatologist based in Alaska, told The Washington Post.

Reasons for this are many. Brettschneider points to all the snow already accumulated during the winter, increased melting of surface snow which makes it unstable, and additional spring precipitation often in the form of rain which adds weight to the top of the snow-pack.

It’s also worth remembering that March is often the snowiest month of the year in a good chunk of the region. On top of that, the Weather Service’s Climate Prediction Center is predicting wetter than normal conditions to continue over the next several months. It seems quite likely there will be more significant avalanches before this historic season comes to an end.