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Train of Atmospheric Rivers to Blast the Sierra with Several FEET of Snow

10/19/2021

Three powerful atmospheric rivers (AR), which are akin to rivers in the sky, will barrel into the Western US in the next 7 days, delivering widespread snowfall as well as much needed moisture to the drought stricken region. This trio of ARs will  make a dent in the drought in the short term, and improve water resource challenges, but will present some additional hazards as well. By the middle of next week, snowfall totals could be substantial enough for some resorts to bump up their opening dates. Right now, the bullseye is on the Sierra, where several feet of snow are likely. Before we get into the details, we wanted to report on another great day in the backcountry of Little Cottonwood Canyon. Another 10" fell overnight, bringing the October total to almost 45", and the conditions were once again excellent. We skinned up around 7 am and rode High Greeley. Check out a clip from the run: Another Deep October Pow Day. Follow our forecaster/rider @lstone84 on Instagram.

We will start this discussion out with the current drought status across the Western US. A large portion of the region is under extreme or exceptional drought, so this parade of storms is most welcome. This series of ARs will most certainly improve the drought status across the West.

(Image courtesy of NOAA)

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Below is a gif showing the precipitable water over the next week. This map shows the ARs that will be impacting the west coast during this time period. Watch them slam into the coast over and over again.

(Image courtest of Weatherbell)

Atmospheric River #1

The first AR will start to impact the west coast today, and continue to do so through Friday. It will bring significant rain to the coastline from British Columbia to California, as well as moderate snowfall throughout this region. The mountains of coastal BC will see significant snow from the first AR. Here is a side by side of snowfall and precipitation of the first AR through Saturday:

(Image courtesy of Weatherbell)

Atmospheric River #1

This will likely be the most impactful of the three atmospheric rivers, especially with its focus on California and the Sierra. This event will last from Monday to Wednesday, and when it's over, the Sierra will be buried. The rainfall will be substantial enough to cause dangerous landslides in recent burn scars. The models have been putting out truly impressive totals for this event, which will be aided by a strong cyclone in the Northeast Pacific. This cyclone not only will pump tropical moisture into California, but will rapidly intensify, becoming a bomb cyclone. This bombogenesis will continue to steer the atmospheric rivers toward the west coast. Below are the rain and snow totals from the GFS for the three day period ending on Wednesday evening.

(Image courtesy of Weatherbell)

Over the last several days, we have seen models produce totals ranging from a few feet all the up to EIGHT FEET. Due to the warm nature of atmospheric river events, snow levels will be pretty high initially, limiting snow to the upper elevations. A better way to get a handle on the range of possibilities for an event like this is to examine the ensembles. Below is the precipitation and snow forecast from the NAEFS ensembles from the University of Utah for the central sierra snow lab.

The large range in precipitation and snow totals across all the members of the ensemble indicate that the confidence is not yet high on exact totals. The precipitation range is 2-15" of rain, while the snow forecast range is 0" to nearly 70". So while its a little difficult to say just how much snow and rain will fall, this AR has the potential to deliver huge quantities of both. Our best guess right now is 3-4 FEET of snow for the upper elevations and 8-12" of rain lower down. We would not be surprised however if these totals increase as we get closer to the storm. As the precipitation and snowfall maps above show, this AR will not solely focus on California. Utah, Idaho, Wyoming, and Colorado will see the benefits from this bomb cyclone enhanced atmospheric river. Initial thoughts are a wide swath of 10-20" in the intermountain western states. This event alone could deliver enough snow for some early resort openings.

Atmospheric River #3

The third AR we will discuss should arrive around the evening Wednesday and last through Friday. The axis of this AR will be shifted, first focusing on Oregon before moving inland and down the coast a bit. Since this is still over a week away, we won't discuss totals yet. This has the potential to deliver massive rainfall and big snow totals as well though.

Beyond the third atmospheric river, the long range data indicates the active pattern will continue, with yet another AR possible. This trio of ARs will deliver desperately needed water to California, much needed snowpack in the Sierra, and widespread significant snow and rain to the Western US. Let us all hope this forecast remains in tact. Make sure to follow us to keep up to date with this series of impressive storms.

 

Luke

 

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We combine 35 years of experience forecasting and chasing powder to provide forecasts that help you find the deepest snow.