Avalanche forecast

Mt Hood

Feb 11 – 12, 2020Northwest Avalanche Center
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Avalanche danger

Thu
Alpine
1 · Low
Treeline
1 · Low
Below
1 · Low
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Highlights

Extreme winds have formed pockets of wind slabs midslope due to recent erratic loading patterns near and above treeline. While unlikely, you may still trigger an avalanche in isolated areas during Low danger. At upper elevations where you encounter a stout icy crust, think about the consequences of taking a hard slide. 

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    1

    Fresh reports from the north and the south side of the mountain tell the same story - wind, wind and more wind. Blowing snow was visible all day and at all elevations with extreme N-NW winds felt even below treeline. While pockets of dense wind packed snow shouldn’t be hard to find Wednesday, triggering a wind slab avalanche will be unlikely given recent mild temperatures and erratic loading patterns. Forecast staff out on Tuesday noted that due to the extreme winds, the most likely place to find wind slabs would be midslope instead of right below ridgelines. Use caution before committing to slopes steeper than 35 degrees where you find stiff or textured snow surfaces. 

    Expect difficult and potentially hazardous travel conditions where you find a stout icy crust. Avoid crossing large steep slopes where a slip could result in a long uncontrolled slide. Ask yourself if you’re equipped and ready to self-arrest even on smaller icy slopes.

Snowpack Discussion

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

If we could choose one word to sum up the last week, and possibly 2020 in general, that word would be fluid. As of February 6, we are in the midst of yet another atmospheric river event, bringing large amounts of low elevation rain and high elevation snow to our region. The WSDOT-SCR avalanche team relayed that this past January has been the wettest on record at Snoqualmie Pass since precipitation records started in the 80s, and it’s their second wettest month on record. With such potent storms, it’s no surprise that our snowpack and avalanche danger has also been fluid, with fluctuations between high and low danger over short time periods. 

February began on the tail end of our largest rain and wind event of the season, with many NWAC weather stations recording wind gusts of over 100 mph and impressive water numbers as high as almost 10 inches in a 48 hour timeframe. 

Maximum wind gusts from weather stations in the NWAC Network Friday 1/31 into Saturday 2/1

This event had freezing levels surge to around 8000 feet across the region, introducing rain to a cold dry snowpack at upper elevations for the first time this season. This included rain above 7000 feet in the Washington Pass area, which had largely escaped the wrath of warmer storms up to this point. Dangerous avalanche conditions during this period produced widespread wet avalanches in most zones as large as D3. Along with Loose Wet and Wet Slab avalanches, Cornices failed naturally, and Glide avalanches were observed in multiple zones.  

Natural glide avalanche (D2) that occurred on a SE aspect at 4400ft on a convex rock slab between Schriebers Meadow and the Railroad Grade. 02/02/20 Photo: Andrew Kiefer

As the rain finally subsided, cold air flooded our region, allowing the wet snow surface to begin to freeze from the top down. This sharp cooldown created what we are calling the 2/1 crust and allowed for Low danger across the region for a few days. The 2/1 crust varies in thickness but should exist in all areas of the region below ~8000 feet and may be considered as our “new ground”. During this period of low danger, most zones picked up modest amounts of low-density snow to overlay the 2/1 crust and even had a bit of sunshine.

Unfortunately, the period of low danger was short-lived, when two days later, another atmospheric river was on our doorstep. This time, the event started off cooler and had lower projected freezing levels. Many zones in the region were able to pick up a foot or more of new snow in all elevation bands before a switch to rain, with upper elevations receiving multiple feet of snow, creating what we are referring to as the 2/4 interface. The setup of heavy fresh snow over the low-density snow sitting on the 2/1 crust was a great recipe for avalanches on its own. Throw in the switch to rain at low and mid-elevations along with high winds and precip rates, and very dangerous avalanche conditions developed across the map on Wednesday the 5th.

This is where we find ourselves on Thursday, in the middle of a notable avalanche cycle producing wet snow avalanches below the rain line with dry snow avalanches above. The way this winter has been going so far, it’s a good guess that things will continue to be fluid going forward, let’s just hope it’s a colder type of fluid.

Loose Wet avalanche activity on Snoqualmie Pass. 02/05/20. Photo: Andy Harrington

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