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Date: 
Sunday, February 4, 2018
Size: 
2
Description: 

I was able to collapse and crack out a small test slope Friday on a north facing piece of terrain at 9200'.  It cracked out about 1' deep and 20' across.  It wasn't particularly representative of most of our terrain and yet there it was:  poor structure, additional wind loading, trigger.  Collapse.  The moderate to strong winds will add just a bit of extra stress to areas of poor structure. 

Our last two persistent slab avalanches occurred on the 31st in upper Alexander Basin and one of them took a heavy load to trigger (an intentional cornice drop that cascaded over a cliffband).  A quick review of the others are below, all essentially north to east facing at 9500' and above.  What's significant is that many(all?) of these close calls have involved very experienced people.  In my view, during these times, it's time to take two steps back from the edge.  Still, we're trending toward dormancy with the persistent slab issues, thus the danger rating of, essentially, low probability, high consequence.  

01/31/2018 Salt Lake region: Avalanche: Alexander Basin, Skier trigger - 16" deep - 70' wide
01/31/2018 Salt Lake region: Avalanche: Alexander Basin, Unknown trigger - 16" deep - 50' wide
01/28/2018 Salt Lake region: Avalanche: West Willow, Skier trigger - 20" deep - 150' wide
01/27/2018 Salt Lake region: Avalanche: Lavina Creek, Unknown trigger - 3' deep - 300' wide
01/26/2018 Salt Lake region: Accident: Upper Meadow Chutes, Skier trigger - 3' deep - 200' wide
01/25/2018 Salt Lake region: Avalanche: Davis Gulch, Natural trigger - 4.5' deep - 150' wide
01/24/2018 Salt Lake region: Avalanche: Pointy Peak, Skier trigger - 2' deep - 100' wide
Type: 
Persistent Weak Layer
Special Announcement: 

The latest UAC podcast - "Recreating Like a Pro - A Conversation with IFMGA guide Anna Keeling" is live. This podcast will be ideal for anyone looking to pick up some tips and tricks from a professional mountain guide for recreating in the winter backcountry environment.

New blog post - Stacking the Deck - a Hindsight 20/40 story

 

Current Conditions: 

Skies vary from partly to mostly cloudy across the range.  Mountain temperatures are in the mid to upper 20s up high, the mid to upper 30s down low.  It's 45°F at our office at the National Weather Service.  With this weather pattern, areas to our north are seeing all the snow while we get left holding the bag.  The bag, in this case, also includes strong wind.  The northwest winds are blowing 30, gusting to 50 even at the mid-elevation ridgelines.  11,000' hourly winds are blowing 50, gusting 60; base area winds are even gusting to near 40.  Riding conditions are not for the faint of heart: corrugated sun crusts, trapdoor wind crust, sandboxing faceted snow, wafer thin rime.  

For January, the Alta Guard station (8700') reported 51.5" of snow with 4.5" SWE  (Snow Water Equivalent). The 74-year January average is 92"/8.6".

Year to date is 109" with 11" SWE (average YTD through January is 250" with 23.3" SWE).

Be sure to read our latest Week in Review for avalanche activity and significant mountain weather events from this past week.

Recent Activity: 

None.  See Greg's Week in Review for more info.

Mountain Weather: 

We should start to see some light precipitation this afternoon/early evening under the northwest flow.  An initial rain/snow line may start as high as 8000', then drop to the valleys by Tuesday.  Decent upper level support adds what it can to a generally weak system, but 2-5" seems reasonable with higher confidence for amounts north of I-80.  Temps for today will be in the upper twenties along the upper ridgelines with northwest winds continuing to blow 30-35mph...increasing to 40mph tonight and tomrrow.  

Bottom Line: 

Most terrain has a LOW avalanche danger.  Isolated areas of MODERATE danger, however, exist on northwest to east facing slopes above about 9000'.  In this terrain, human triggered avalanches 1-3' deep are possible.  Additionally, shallow pockets of soft and hard wind slab are littered across the landscape, but most problematic in high consequence terrain.  Lastly, damp push-alanches are possible in steep low to mid-elevation sheltered slopes that have remained warm for the past several days. 

Size: 
1
Likelihood: 
1
Likelihood: 
1
General Announcements: 

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This information does not apply to developed ski areas or highways where avalanche control is normally done. This advisory is from the U.S.D.A. Forest Service, which is solely responsible for its content. This advisory describes general avalanche conditions and local variations always occur.

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