Avalanche Forecast

Issued: Jan 6th, 2020 10:31AM

The alpine rating is high, the treeline rating is high, and the below treeline rating is considerable. Known problems include Storm Slabs and Loose Wet.

Northwest Avalanche Center NWAC, Northwest Avalanche Center

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Expect very dangerous avalanche conditions Tuesday as one storm ends and another begins, adding to already impressive water amounts. Rain below and near treeline and heavy snow loading up high will continue to rapidly destabilize this snowpack until we get a break in the weather. Travel in the mountains is not recommended during this time period.

Summary

Snowpack Discussion

January 02, 2020 (The regional synopsis is updated every Thursday @ 6 pm)

Happy New Year! 

The pacific northwest rung in the new year with a winter storm cycle that brought changing conditions to our region. This storm exhibited three characteristics: warm, wet, and windy. Let’s take a look at the end of 2019, the beginning of 2020, and where we can go from here. 

Wrapping up 2019

The last few days of December were generally quiet and cold. The snowpack seemed to enjoy this break in the weather. Lingering unstable snow from the pre-Christmas storms gained strength, persistent weak layers appeared to stabilize, and avalanche hazard decreased in all forecast zones. All in all 2019 ended quiet and uneventful… until the New Year’s Eve weather party showed up …  

Quiet weather led to lower avalanche danger during the last week of 2019. Hogsback, White Pass, WA. Photo: Andy Harrington

Blowing into 2020

A warm, wet, and windy weather system blew into the northwest for New Year’s Eve and New Year’s Day. This brought rapidly changing conditions and increasing avalanche hazard to all areas. 

  • Warm: Unfortunately this system brought with it warm air. Freezing levels measured near the coast reached 9000’ on the afternoon of the 31st. Many weather stations recorded above freezing temperatures during the onset of precipitation. 

  • Wet: While this system wasn’t as wet as the atmospheric river prior to Christmas, it still produced impressive water numbers in many areas. The bulk of the precipitation seemed to be focused on the Passes and Volcanoes, and water spilled over the crest to places like Washington Pass and Leavenworth. Sadly, when combined with the warm temperatures, this translated to rain well into the near treeline band (or higher) for most areas. The main exception appeared to be in the northeastern cascades, where locations like Washington Pass remained all snow. 

 

HurRidge

MtBaker

WaPass

Stevens

Leavenworth

SnoqPass

MtRainier

MtHood

Precipitation (in)

1.84

3.39

1.42

4.56

1.06

6.19

5.39

5.41

Snow (in)

-

15

-

12

0

3

10

8

Table 1: Precipitation and storm totals from selected weather stations during the New Year’s Eve Storm. “-” 24hr storm snow not measured. 

  • Windy: While the warm and wet were impressive, it’s the winds that may set this storm apart. Most weather stations recorded very strong and extreme winds during the storm. Alpental exceeded 100mph just after midnight to ring in the new year. Any dry snow at high elevations was redistributed by the wind and snow surfaces were transformed. 

Table 2: Wind speeds from New Year’s Eve from selected wind sites. Note the sustained period of winds between 40-60mph.

Eventually, temperatures cooled, the rain turned back to snow, and winds calmed. Many locations picked up additional snow as the storm wound down, but 2020 was already off and rolling with its first major storm.

New Year’s Resolutions

The active weather pattern that started the new year appears to continue. The snowpack and avalanche conditions will continue to change. So, what can your New Year Avalanche Resolutions be? 

  1. Read the forecast. This is a great way to monitor conditions even if you aren’t heading into the mountains. 

  2. Get out in the snow! Enjoy the wonderful mountains in your backyard. 

  3. Submit an observation. Tell the avalanche center what you saw while out in the snow by submitting an observation and sending in a photo. 

Thanks for all of your support in 2019 and here’s to 2020!

-Dallas

 

Problems

Storm Slabs

An icon showing Storm Slabs

Large natural avalanches are likely on Tuesday at all elevations as forecasted precipitation and strong winds continue to increase slab depth. On Monday, NWAC observations in the Crystal backcountry revealed multiple natural avalanches up to D2 in size and close to 3 feet of storm snow, with similar observations from White Pass Ski Patrol. Paradise has even more impressive numbers with 5 inches of water and 70 inches of snow since Friday. Expect multiple density changes to exist within the storm snow and deeper slabs as you ascend in elevation, particularly above ~5000 feet or in areas that receive more precipitation, such as Paradise. Avoid travel on or beneath slopes steeper than 30 degrees, and steer clear of avalanche path runout zones.

Release of a soft cohesive layer (a slab) of new snow that breaks within the storm snow or on the old snow surface. Storm-slab problems typically last between a few hours and few days. Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

 

You can reduce your risk from Storm Slabs by waiting a day or two after a storm before venturing into steep terrain. Storm slabs are most dangerous on slopes with terrain traps, such as timber, gullies, over cliffs, or terrain features that make it difficult for a rider to escape off the side.

 

Storm slabs usually stabilize within a few days, and release at or below the trigger point. They exist throughout the terrain, and can be avoided by waiting for the storm snow to stabilize.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

1 - 1

Loose Wet

An icon showing Loose Wet

Loose Wet activity will peak Monday night into Tuesday morning due to warming below ~5000 feet. Loose Wet avalanches are capable of entraining lots of snow and running far distances, even on low angled slopes. Rollerballs and pinwheels are signs that Loose Wet avalanches are possible. Avoid traveling in and below all avalanche terrain with unconsolidated snow surfaces or at the onset of rain on snow.

Release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

 

Travel when the snow surface is colder and stronger. Plan your trips to avoid crossing on or under very steep slopes in the afternoon. Move to colder, shadier slopes once the snow surface turns slushly. Avoid steep, sunlit slopes above terrain traps, cliffs areas and long sustained steep pitches.

 

Several loose wet avalanches, and lots of pinwheels and roller balls.

Loose wet avalanches occur where water is running through the snowpack, and release at or below the trigger point. Avoid terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.

Elevations: Treeline, Below Treeline.

Likelihood

Likely

Expected Size

1 - 1

Valid until: Jan 7th, 2020 10:31AM