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We Asked a Meteorologist What an Atmospheric River is and How it’s Affecting Snowfall

Stormageddon, Snowpocalypse, Snow of the Century — whatever you want to call it, there's no denying the recent storm systems have produced historic snowfall and weather across much of the United States and Canada.

These winter storms have dropped insane amounts of snow rapidly and have caused numerous resorts to close operations and dig out. There's been power outages, flooding, ice storms, road closures and avalanches that have crippled towns from west to the east.

Recent weather forecasts predict more moisture is on the way, and Mother Nature is making a stand that she's just not willing to stop. It's great for us snowboarders, as many of us are having some of the best powder days of our lives, but why? What is causing these super deep conditions and volatile weather?

With questions looming, we reached out to meteorologist, Cory Gates, from AspenWeather.net with a slew of queries about these recent storms, and what we can still expect. Scroll on for our conversation below and scope more weather stories from this storm here.

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What the heck are we experiencing right now with all of these storms? It seems like Mother Nature just has the faucet on…

What we're experiencing is the result of an atmospheric river.

Can you walk us through what an atmospheric river is, and what it does?

Basically, an atmospheric river,  is about a 300 or 400 mile wide and often over a thousand miles long area of enhanced ambient water or moisture. Under the right conditions, this can set up out in the Pacific Ocean and traverse easterly toward land. This atmospheric river has caused the Sierra to be so wet and snowy this winter. It weakens a bit after the river plows in California, but lot of that moisture has continued to travel east into the Rockies, which is why we're seeing such enhanced snowfall.

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These guys have been getting so much action. Photo: Peter Morning

When was the last time we experienced this weather phenomena?

In terms of the atmospheric river, it happens more often than you might think.  I would say it happens a few times each winter. The difference is that it hits different locations each winter with different intensities.

What are the factors allowing for so much snow across the country right now?

Factors allowing for a snowy western US, including Colorado and Utah, is that this winter is a weak La Nina with a warm PDO.  PDO stands for Pacific Decadel Oscillation.  All the PDO means is we have warmer than normal sea surface temps over all of Alaska down to off Vancouver and then off Washington and Oregon. The weak La Nina means the equatorial pacific is slightly colder than normal. The warm water off Alaska causes what is called High Latitude Blocking, this means a big stubborn upper air high gets stuck up there. This big upper air high forces the jet to come underneath it and we get systems ramming into the west from California eastward. It's the perfect recipe to make conditions snowier than normal.

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Mammoth has received a whopping 248" of snow this season. Photo: Peter Morning

Long term and short term weather, what can we expect? How much more snow could potentially be on the way?

I see another batch of high latitude blocking taking place over Canada for the rest of January.  There is not much doubt that January ends up a good month with continued snow at many resorts. February could be more tricky. It depends on the location of the blocking aloft— my guess is the east coast has some decent action, but we also have normal to maybe slightly above normal snow, which is still good. Getting a feel for spring (March/April) is too difficult to call right now.

In terms of this type of snow, does it have higher moisture content?

It has not been super cold for the winter overall, so because these systems have come from California,  they contain a lot of ambient water, so much of the snowpack is dense and contains more water than normal.  This is actually good for a great spring runoff if we can keep the snow going. Wetter snow is also harder to melt, so it hangs in there longer.

Can you give us some stats on Colorado snowpack?

Our current snowpack statewide in Colorado is 147% of normal. That's just a number, but let's look at it this way: Only 3 times in the last 40 years has the statewide snowpack reached 150% of normal by February 1st. We will be close to that this year if we have another storm or two before January is over.

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Shacktown. There's plenty out there. What's your excuse for not getting some of it? Rider: Forrest Shearer Photo: Andrew Miller

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