Northwest Avalanche Center NWAC, Northwest Avalanche Center

Cascades - South East Avalanche Forecast

Jan 11th, 2020 10:00AM

Another round of heavy snow is on the way Saturday night and Sunday and will maintain dangerous avalanche conditions. You will be able to trigger avalanches large enough to bury, injure, or kill you. If you do travel in the backcountry stick to ridges and low-angle slopes. Avoid travel on or underneath slopes steeper than 30 degrees.

Summary

Discussion

Strong winds will rapidly transport new snow and build fresh wind slabs on lee slopes at upper elevations especially near the cascade crest. You will be able to trigger large and dangerous avalanches on slopes where you see signs of wind transported snow such as cornices, and pillow-like drifts of snow. Avoid travel on or below slopes steeper than 30 degrees.

At lower elevations, new snow is stacking up this evening and more is expected Friday night. With heavy snowfall continuing Saturday, remember that you are most likely to trigger storm slabs during periods of continued heavy snowfall. If you see evidence of natural avalanches, even small ones, that’s a clue that storm slabs will exist on all slopes. Look for cracks shooting through the snow or strong snow above weak snow. When you see these signs, choose lower angle terrain less than 30 degrees.

With cold temperatures and lots of new snow, you may find wind-sheltered areas with deep uncohesive loose snow. These loose snow avalanches or “sluffs” can be large enough to push you over or knock you into tree wells or open creeks. Be aware of stopping below steep slopes or above hazards like creeks and cliffs.

Even away from avalanche slopes, hazards exist such as snow immersion suffocation. Make sure you’re informed and travel with a partner. https://www.deepsnowsafety.org/

A small, but deep storm slab observed at Mt Hood Saturday. Similar conditions are expected in the East-South Zone on Sunday. Photo: Heiko Stopsack

 

Forecast Schedule and No Rating definition

We do not have enough specific snowpack information to issue an avalanche hazard rating for the East South zone. However, even when No Rating is applied, applicable avalanche conditions and backcountry travel advice will be provided throughout the season - this forecast is updated every day, all winter long!  When weather systems produce very dangerous avalanche conditions in adjacent zones, NWAC will issue an avalanche warning for this zone as well.

Snowpack Discussion

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

Valid until: Jan 12th, 2020 10:00AM