Avalanche Forecast

It’s difficult to pinpoint the location or exact nature of avalanche problems you’ll encounter on Wednesday. What we know is that there’s a lot of low-density snow out there. Strong to very strong ridge-top winds peaking Wednesday evening, but lingering into the morning hours, should have created large slabs on a variety of aspects (including perhaps unusual W aspects). Feel for stiffer layers, or even sounds hollow under your feet to confirm this problem. Heavy snowfall Wednesday into Wednesday night with shower activity into Thursday leads to storm instabilities (storm slabs or loose dry). Keep in mind that slabs can form with a change in snow crystal type or even a very subtle density change, and at these cold temperatures, weaknesses persist for several days. Small test slopes may be the best way to identify these problems. Recognize that as snow continues to pile up with lighter winds on Thursday, avalanche problems may be hard to visually identify. 

While we are most concerned about the new snow, without recent observations on the ground, we don’t know whether instabilities may have persisted below the new/old snow interface. Sheltered terrain in the trees limits your exposure to the dangerous avalanche conditions.

Even (or especially) in the trees, deep snow hazards are real and exist at all elevations. Before heading out, learn about tree well or snow immersion suffocation risks and travel with a partner (www.deepsnowsafety.org). Also, be prepared for some of the coldest temperatures seen this winter with winds creating frost-bite conditions that would make a rescue far more serious.

The last crust at Hurricane Ridge was formed on January 7th and since then we’ve nearly doubled the snowpack at Hurricane Ridge and with a low-density upper snowpack we are at 133% of normal snow depth for January 15th. Over the last week, temperatures at Hurricane Ridge have been unseasonably cold, with a modified arctic air mass over the region since last Sunday evening. Several storm systems brought 2.3” of snow water equivalent Friday through Monday morning. Since then, very cold and low-density snow accumulated periodically, primarily Tuesday night when up to two ft of snow accumulated in Port Angeles and the 0.31” of snow water equivalent picked up at Hurricane Ridge may have resulted in similar storm totals at this elevation. Snow started up again Wednesday afternoon with winds increasing and averaging 25 mph with gusts into the 30’s by 4PM. These weather trends are illustrated in the plot below.

 

 

Forecast Schedule

For the 2019-20 winter season, avalanche danger ratings will be issued for the Olympics every Friday through Sunday and during mid-week holidays. During the week, No Rating will be issued but forecasts will include expected conditions and relevant travel advice.  If you are out in the Olympics, share your backcountry observations with us and the greater community.

January 12th update: In the past week, there have been two fatal avalanche accidents to the east of NWAC's forecast area. One occurred near Kellog, ID and another outside of Baker City, OR. Local avalanche centers will perform accident investigations including final reports. You can find preliminary accident information at avalanche.org.

January 9th, 2020 (The regional synopsis is updated every Thursday @ 6 pm)

As we said Happy New Year and rang in 2020, snow was turning to rain at many trailheads and lower elevation Passes, not exactly the fresh start winter recreationalists had in mind. The snowpack was already looking a little thin throughout the region, especially at lower elevations. Low snow in places like Snoqualmie Pass made backcountry travel difficult and hazardous.  NWAC’s snow depth climatology report was showing snow depths 25-64% of normal to kick off the start of 2020.

Things can change quickly in the Pacific Northwest and they did as we entered an extended storm cycle between January 2nd to January 8th. Strong winds, fluctuating temperatures, and heavy precipitation offered few breaks in the weather over this period limiting observations and hampering travel. Despite periods of rain at lower elevations, most areas saw several feet of new snow with big jumps in total snow depths as a westerly storm track strongly favored the West Slopes of the Cascades and the Olympics for the highest precipitation totals.

Location

Total Snow Depth (in) 1/2/20

Total Snow Depth (in) 1/8/20

Hurricane Ridge

31

51

Heather Meadows Mt Baker

55

95

Washington Pass

49

74

Stevens Pass

41

63

Snoqualmie Pass

22

33

Alpental mid-mountain

44

63

Crystal Mt Green Valley

40

66

Paradise Mt Rainier

54

105

White Pass Upper

43

69

Timberline

36

57

Mt Hood Meadows

36

53

 

We may have started with a shallow snowpack, but most locations increased their snowpack by 70% or more over this storm cycle!

During this extended and impressive storm cycle that included backcountry avalanche warnings, natural avalanches were reported in many areas Jan 6th-7th.

The Stevens Pass area was especially active over the period with over 100(!) avalanche observations made on the 6th and 7th. Professionals reported numerous avalanches in places that they hadn't previously observed avalanches and some paths avalanched multiple times in a 24 hour period. Observers reported a few very large (size D2.5-3) avalanches, originating at upper elevations with deeper crowns that likely formed from wind drifting. Topping off an active couple of days, warming temperatures lead to a widespread loose wet avalanche cycle.

The southern Washington Cascades, the Wentachee Mountains and Mt. Hood either saw less precipitation, warmer temperatures leading to more rain than snow, or some combination of the two and ended up with relatively less active avalanche conditions than areas further north. 

A large natural avalanche on Rock Mountain near Berne along Hwy 2 east of Stevens Pass that released Jan 6th or 7th. Photo: Josh Hirshberg 1/7/20

Many small storm slabs released in the Crystal backcountry 1/6-1/7. Pinwheels in the photo suggest loose wet avalanche activity occurred when temperatures rose above freezing and snow turned to rain.

Another active and colder weather pattern is on it’s way. Enjoy yourself out there and be sure to check the forecast before heading out. Remember, NWAC is a community-supported avalanche center and when you submit an observation you make the forecast better!

-Peter Moore

It’s getting deeper! Photo: Jeremy Allyn