Avalanche Forecast

A recent storm deposited variable amounts of snow on Friday through Saturday, with many locations picking up over a foot of cold, low-density snow. Moderate to strong E and NE winds have continued even after the precipitation waned. 

Monday will be the first day of multiple days of warming and the new snow should weaken at some point due to solar input and run on the crust. Which slopes reach their tipping point on Monday remains to be seen, but it is likely to happen at some point this week. The most rapid warm up occurs on Monday and that has us concerned given all the recent snow. These avalanches could be large in isolated areas or could start small before entraining snow and triggering slabs as they descend, creating larger avalanches. If you notice signs of these avalanches such as rollerballs, snow shedding from trees and rocks, or avalanches with fan-shaped debris, then seek out shaded terrain and be aware of sun-exposed slopes above you. Cornices will also be affected by the warm-up and may fall, triggering slabs or starting Loose Wet avalanches. Give cornices a wide berth by not traveling on or below them. 

Winds Slabs have been reactive over the weekend in neighboring zones and surprised a number of travelers due to atypical loading patterns and sensitivity. NWAC forecasters at Paradise on Sunday observed naturally triggered Wind Slabs and were easily triggering slabs up to 16” deep on test slopes. Look for cross-loading and mid-slope loading to have created dangerous pockets of snow in features not generally on your radar. You can look for textured snow surfaces or freshly built cornices to help you determine wind-loaded features that you should avoid. Use hand-pits and test slopes to check the bond between wind-blown snow and the crust before stepping into any consequential terrain.

A human triggered avalanche near Blewett Pass in the East Central zone Saturday. Diamond Head, NW 5200’, Photo: Adam Butterfield. 

Prior to this storm numerous rocks, trees, stumps, and even bare ground could be found at mid and lower elevations. Travel slowly to give yourself time to react to some of these shallowly buried obstacles. 

March 12, 2020 (The regional synopsis is updated every Thursday @ 6 pm)

From March 6th to the 12th the Pacific Northwest experienced a few small storms and a few notable days for people and avalanches. Light to moderate snow accumulated slowly over a period of a few days, and avalanche danger increased from Low to Moderate over the weekend of March 8th. The exception was the West North zone, which won the snowfall competition this week. 18-24” of new snow was observed in the Mount Baker area on the 6th, and 10” of new snow on the 11th. Avalanche danger reached Considerable there for storm slab, wind slab, and loose wet avalanche problems. 

People, complicated avalanche terrain, and lots of avalanches. Bagley Lakes Basin, West North zone. Photo by Nathan Resick, March 8, 2020.

Loose dry slides initiated by skiers in big terrain. No one was caught or carried. East Central zone. March 8, 2020. Matt Primomo photo.

The snow fell with minimal wind, and accumulated slowly over firm suncrusts or wind stiffened surfaces. Thicker cloud cover inhibited the sun in areas where 4” to 12” of snow accumulated over the course of a few days. Cold overnight temperatures allowed the low density snow to weaken. By the 8th, the clouds broke up enough to allow strong radiation to change snow surfaces. When the sun finally did hit the snow, it quickly caused loose avalanches in steep terrain. 

An active weekend for people and avalanches: 

Many areas experienced some form of loose avalanche activity from March 6th to 9th.  Sunday, March 8th was the day that recorded the most widespread avalanche activity across the region. The size of these avalanches were directly related to the amount of new snow that had recently accumulated in that area, and the size of the terrain. 

West North zone on March 8, and West South zone on March 8th. Uphill and downhill tracks got covered by debris. Photos by Zack McGill and Dallas Glass.

We as a community can look back at, and learn from these few days. Numerous human triggered slides occurred, some were slabs but the majority were loose. A number of catch and carries were observed, and many more likely went undocumented. Luckily, no injuries or burials were reported. Observers across the region reported lots of instances where previous tracks got hit with debris, either from human triggered or natural avalanches. 

As the days get longer and folks begin to step into the alpine zone and bigger terrain more frequently, it is important to keep a humble attitude. Continuously evaluate route selection with potential for loose wet and cornice falls in mind. Check the mountain weather and avalanche forecasts for the most up to date info. Enjoy the backcountry, be safe, and let us know what you see out there!

-MP

Solo snowboarder aired into this slope, and went for a ride but was not buried or injured. Slide took out the corner of a skin track. Bagley Lakes Basin, March 8, 2020, Zack McGill photo.

Wind slab triggered by a skier at 7,500ft next to the popular route on Mt St Helens. The skier wasn’t caught or carried. Andy Goodwin photo, March 8, 2020.