Issued: Sat, Mar 03, 2018 at 7AM

Expires: Sun, Mar 04, 2018

Above 3,500ft Moderate

2,500 to 3,500ft Moderate

Below 2,500ft Moderate

Degrees of Avalanche Danger ?

1. Low
2. Moderate
3. Considerable
4. High
5. Extreme

Avalanche Danger Rose ?

Avalanche Problems ?

Problem Details

BOTTOM LINE

A Moderate Avalanche Hazard, on all aspects and elevations, exists for Persistent Slab Avalanches today.  The Valentines buried persistent weak layer is still the main concern. A Low Hazard, increasing to Moderate Hazard, exists for Dry Loose avalanches on steep, wind protected terrain at mid and upper elevation with the addition of new snow Friday evening and Saturday.

 


 

PERSISTENT SLAB AVALANCHE PROBLEM

A Moderate Avalanche Hazard exists for Persistent Slab avalanches at all elevations on all aspects, on slopes 35º and steeper.  Expect avalanches to be up to D2 in size, and 1-3 feet deep. Evidence of this layer exists in portions of terrain, but is not always obvious. This problem will most likely be stubborn to trigger. 

 

Poor snowpack structure within the Valentines weak layer is the primary concern.  10-12″ of new snow from 2/26 came in with shifting winds distributing the new snow in a complex pattern on many aspects. This snow has bonded well to the old snow surface and is presently not an avalanche concern.  Deeper in the snowpack, the Valentine’s storm layer continues to be more reactive on southerly aspects with thinner snowpacks and buried crusts. Some activity on other aspects indicates a spatially variable distribution of this avalanche problem which is tricky and difficult to predict. Evidence of instability may be difficult and spotty to find, especially with few new inches of snow overnight.  While there is low probability for triggering an avalanche, the consequence of triggering a 1-3 foot deep avalanche could be high. The potential outlier avalanches do exist on steeper leeward aspects, previously wind loaded earlier in the week. See obs here. Pics here.

Recent stability tests confirm poor structure, moderate strength, and low to moderate propogation potential. Reported observations may lack evidence of avalanche activity, however, this does NOT mean human triggering high consequence avalanches are not possible. Avoiding this kind of avalanche problem may require a fair bit of luck, along with your skill, for this long term lingering persistent slab problem.

 

Marmot, W, 4300′, 32º slope:

 


LOOSE SNOW AVALANCHE PROBLEM

Loose snow avalanches will be small to moderate in volume, and possible to trigger on wind protected slopes 40º and steeper. New snow from 2/26 that remains protected enough to sluff combined with 2-3″ Friday night and 3-4″ projected for today, will have the ability to sweep you off your feet and carry you into more consequential terrains traps. As snowfall accumulates through the day, expect loose dry avalanches to increase in volume.  Terrain choice and sluff management will be good aides in avoiding these avalanches.

 

Recent Avalanche Activity

Numerous natural avalanches were observed and reported mid-storm 2/26. Most naturals occured on SE, S, and SW aspects at mid and upper elevation. See observations.

One snowmachine triggered slab avalanche was reported 3/1 on a NW aspect at 4000′. See observations.

Numerous small to medium dry loose sluffs were observed after the storm.

 

3/1 Snowmachine triggered avalanche NW aspect 38º . Sno-go was able to outrun avy, no injuries.

 

Naturals mid-storm 2/26 ,Marmot area above Archangel

Some areas have 12″ or more of new snow- others are scoured to the tundra. 3/2

Wind effect and stiff 1F to 4F hard wind slabs near ridgelines 3/2

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Recent Weather

This week’s weather at 3550′:

Temps averaged 8ºF, with a low of -3ºF and a high of 21ºF.

IM reported 10″ of new snow this week with 0.9″ of water (SWE) on 2/26.

Winds at IM reported gusting NW 37mph 2/26, SE 24 mph 2/27, and SE 20 mph on 2/28.

Overnight at 3550′:

Temps averaged 20° F.

2-3″ new snow overnight.

This week’s weather at 4500′:

Temps averaged 7ºF, with a low of -5ºF and a high of 24ºF.

Winds averaged SE 4 mph, max SE 15 mph . Gusts averaged SE 11 mph, max gusts S/WSW 34 mph. Winds varied throughout the storm from E to WSW at Marmot Station.

Overnight at 4500′:

Temps averaged  20ºF overnight, with a Low of 18ºF .

Winds averaged SE/SSE 4 mph overnight, with a max gust SE/SSE 11 mph.

 


NWS recreational forecast for Hatcher Pass here


NWS point forecast here


State Parks snow report here

Additional Info & Media

The avalanche hazard will likely remain the same through the weekend.

If we see more snowfall than expected, or strong winds, the hazard will increase.

NWS is calling for 3-4″ of snow at Hatcher Pass today, temps 19-26º, and light southerly winds 2-13 mph.

 

 

Posted in HPAC Forecasts.
Allie Barker

Forecaster: Allie Barker