Issued: Sat, Mar 10, 2018 at 7AM

Expires: Sun, Mar 11, 2018

Above 3,500ft Considerable

2,500 to 3,500ft Moderate

Below 2,500ft Low

Degrees of Avalanche Danger ?

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

Avalanche Danger Rose ?

Avalanche Problems ?

Problem Details


A Considerable Avalanche Hazard exists for Wind Slabs on leeward aspects, mostly West to North, at mid and upper elevation on slopes above 35º.

A Moderate Avalanche Hazard exists on all aspects and elevations for Persistent Slab Avalanches on slopes above 35º.

 It will be possible for wind slabs to step down into the old persistent slabs today. Take note: We have seen 3 human triggered avalanches in the past 3 weeks, all caught and carried, 2 buried, and no injuries. The persistent weak layer is the culprit for all these unintentional avalanches.



A Considerable Avalanche Hazard exists for Wind Slab avalanches today at mid and upper elevations, on West through North aspects, on slopes 35º and steeper. 10″+ new snow this week combined with increasing winds, gusting E/ESE 26-38 mph on 3/8 and 3/9 have formed slabs 6-12″ thick. Expect mostly small avalanches, D1 to D2 in size

Several natural wind slabs were observed on 3/9 on west and northwest aspects around 3500-4000′. Instability exists in portions of terrain. Expect wind slabs to be touchy, near and below ridgelines and on gully sidewalls.  Visual surface clues like sastrugi or wind sculpted terrain, and poles tests that identify upside down snow, or shooting cracks-  will be bulls-eye clues of instability. It will be possible for wind slabs to step down into the deeper, weaker persistent grains under the Valentines Day layer. This could be 2-3 feet deep in some locations.

Stability tests on recent wind slabs show easy propagation on isolation.  The good news: wind slabs tend to heal relatively quickly once the wind stops blowing.  As the peak of Friday’s wind activity begins to taper this morning, natural avalanche activity will begin to subside.


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 2-3 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. 

The persistent slab problem we persistently talk about is not going away. However, it is getting buried deeper in the snowpack. The good news: it will be harder to trigger because of its depth. The bad news: if you trigger it, the consequences could be huge. The reason we are not seeing larger avalanches in this PWL is likely due to spatial variability in the snowpack.

This problem continues to be a low probability/high consequence risk. Stability tests require a lot of force to get this persistent weak layer to fail, however, poor structure still exists. Larger loads, such as snow machines, may have better chances for triggering a persistent slab. Triggering a persistent slab is more likely where the slab is thinner, which is difficult to identify and avoid. Many people may successfully ride a slope before someone finds a trigger point.

Are we good, or just lucky? This type of avalanche problem is difficult to assess and will require a certain amount of luck to safely mitigate.  If you are already going to tangle with this beast, maximize your safety with safe travel protocol, choose more conservative terrain, and carry and be proficient with avalanche rescue gear.

As friend and forecaster, Drew Hardesty always says, “Terrain is your friend.” Use it to your advantage, choose terrain wisely.  Ride one person on the slope at a time. Get out of the way at the bottom of the slope. Use communication devices and agree on safe zones ahead of time.  Route choice is your best choice.  Hard slab persistent avalanches may run farther than you anticipate.


The weak layer is over 3 feet deep in this specific location.

See Pit


Recent Avalanche Activity

3/6-3/7  Numerous loose snow avalanches (sluffs) were observed earlier in the week after 6″ of new snow on 3/6. Sluffs were observed on all aspects at mostly mid and upper elevation on slopes above 40º. Sluffs ran on old sun crusts on southerly aspects and old wind crusts on leeward aspects and were D1-D1.5 in size.

3/9 Natural wind slabs failed on new snow/old snow and also stepped down to old persistent grains. Wind slabs were observed on Marmot W/NW aspects and NW Arkose Ridge line and were D1-D2 in size.

Nosehairs- natural sluff 3/7 S 4500′


NW /W sluffs lower microdot 3900′ 3/6


Naturals 3/9


3/9 Arkose Ridge NW 4000′ Natural wind slab appears to have stepped down to old persistent slab and triggered sympathetic avy below. Debris ran to top of icefall.





Arkose Ridge , natural wind slab 3/9 NW 4000′

3/9 Marmot, W aspect 4000ft. Natural wind slabs. Observed increase in wind, flagging, and significant wind transport, then watched these avalanches occur.

3/9 Marmot, NW/W 4000′ natural wind slab





Recent Weather

This week’s weather at 3550′:

Temps averaged 17ºF, with a low of 8ºF and a high of 25ºF.

IM reported 10″ of new snow this week with 0.6″ of water (SWE) on 3/6 and 3/8.

Winds at IM reported gusting ENE/NE 17-31 mph on 3/9.

Overnight at 3550′:

Temps averaged 15° F.

No new snow overnight.

This week’s weather at 4500′:

Temps averaged 14ºF, with a low of 7ºF and a high of 21ºF.

Winds averaged SE 7 mph, max SE 23 mph . Gusts averaged SE 13 mph, max gusts E 38 mph.

Overnight at 4500′:

Temps averaged  12ºF overnight, with a Low of 11ºF .

Winds averaged SE 12 mph overnight, with a max gust SE/SSE 32 mph.


NWS recreational forecast for Hatcher Pass here

NWS point forecast here

State Parks snow report here

Additional Info & Media

Expect the avalanche hazard to decrease to Moderate as winds diminish and wind slabs start to bond to old snow surfaces on Sunday.

NWS is calling for a trace of snow at Hatcher Pass today, temps 15-23º at 3000′, and winds E 4-11 mph.

Sun and warming temps Sunday could increase avalanche hazard on southerly aspects Sunday.



Posted in HPAC Forecasts.
Allie Barker

Forecaster: Allie Barker