Hatcher Pass Avalanche Center
Hatcher Pass

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ARCHIVED - Forecasts expire after 24 hours.
Issued
Sat, April 10th, 2021 - 7:00AM
Expires
Sun, April 11th, 2021 - 7:00AM
Forecaster
Allie Barker
Avalanche risk The Bottom Line

The avalanche danger is LOW today on all aspects, at all elevations. Low danger does not mean no danger. Small wind slabs will be possible to human trigger in isolated terrain, on SE to S to W aspects, at upper elevation. This problem will be quick to heal.

Below freezing and single digit temperatures this week have resulted in at least one case of frostbite on Frostbite peak. Cold temps have also assisted in increasing the stability in the snowpack. The persistent slab problem is temporarily dormant. Stay tuned for the next episode of the persistent slab problem!

The road will remain closed this weekend at Mile 11 due to avalanche debris on the road. There is some uncertainty as to how long DOT will keep the road closed.  Due to upper elevation being largely inaccessible this week, most observations have occurred at low and mid elevation.

As a reminder, avalanche advisories are valid for a 24 hour period. Without an additional load on the snowpack from precipitation, wind, or rapid warming, avalanche danger generally improves within 24 to 48 hours.

Special Announcements

HPAC’s last forecast will be Saturday, April 17th. We will continue to monitor the observation platform through the end of the season.  HPAC will continue to publish updates as necessary.

Thank you for your support this season. It is not too late to DONATE.  We depend on your community support!

Sat, April 10th, 2021
Upper Elevation
Above 3,500'
1 - Low
Avalanche risk
Mid Elevation
2,500'-3,500'
1 - Low
Avalanche risk
Low Elevation
Below 2,500'
1 - Low
Avalanche risk
0 - No Rating
1 - Low
2 - Moderate
3 - Considerable
4 - High
5 - Extreme
Avalanche risk Avalanche risk Avalanche risk Avalanche risk Avalanche risk
Travel Advice Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features. Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern. Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding, and conservative decision-making essential. Very dangerous avalanche conditions. Travel in avalanche terrain not recommended. Extraordinarily dangerous avalanche conditions. Avoid all avalanche terrain.
Likelihood of Avalanches Natural and human-triggered avalanches unlikely. Natural avalanches unlikely; human-triggered avalanches possible. Natural avalanches possible; human-triggered avalanches likely. Natural avalanches likely; human-triggered avalanches very likely. Natural and human-triggered avalanches certain.
Avalanche Size and Distribution Small avalanches in isolated areas or extreme terrain. Small avalanches in specific areas; or large avalanches in isolated areas. Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas. Large avalanches in many areas; or very large avalanches in specific areas. Very large avalanches in many areas.
Recent Avalanches

Numerous large and very large natural avalanches were observed on Sunday after 11″ of new moist snow with 2″ of SWE from SSW,SSE,W winds gusting 20-40 mph for 24 hours. Pictures from Sundays Easter Avalanche Cycle are available HERE.

No new avalanches have been observed or reported since Sunday. Even though most of HP is inaccessible right now, we still believe that no recent avalanches have occurred since Sunday.

Below are more natural avalanches from Easter Sunday 4/4

4/4 WNW 3800′ Backside of Frostbite, Government bowl

 

4/4 E aspect, 4000′, sunnyside of govt

 

4/4 E to S aspects, south end of Frostbite, 3600′

 

4/4 NE 4500′ Government

 

Avalanche Problem 1
  • Wind Slabs
    Wind Slabs
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    Size
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Likelihood of Avalanches
Terms such as "unlikely", "likely", and "certain" are used to define the scale, with the chance of triggering or observing avalanches increasing as we move up the scale. For our purposes, "Unlikely" means that few avalanches could be triggered in avalanche terrain and natural avalanches are not expected. "Certain" means that humans will be able to trigger avalanches on many slopes, and natural avalanches are expected.
Size of Avalanches
Avalanche size is defined by the largest potential avalanche, or expected range of sizes related to the problem in question. Assigned size is a qualitative estimate based on the destructive classification system and requires specialists to estimate the harm avalanches may cause to hypothetical objects located in the avalanche track (AAA 2016, CAA 2014). Under this schema, "Small" avalanches are not large enough to bury humans and are relatively harmless unless they carry people over cliffs or through trees or rocks. Moving up the scale, avalanches become "Large" enough to bury, injure, or kill people. "Very Large" avalanches may bury or destroy vehicles or houses, and "Historic" avalanches are massive events capable of altering the landscape.

Signal Word Size (D scale) Simple Descriptor
Small 1 Unlikely to bury a person
Large 2 Can bury a person
Very Large 3 Can destroy a house
Historic 4 & 5 Can destroy part or all of a village
More info at Avalanche.org

Small winds slabs 1-3″ thick will be unlikely in most locations, but possible to human trigger in isolated locations on SE to S to W aspects at upper elevation today. For the most part, HP was spared by the loathed yet anticipated wind on Friday. Moderate winds gusted 20mph for 4 hours from the E and NW at 3500′. Limited information is available above 3800′ due to the road being closed.

This problem will be quick to heal.

Additional Concern
  • Persistent Slabs
    Persistent Slabs
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
More info at Avalanche.org

Even though the persistent slab is not expected to be a problem today, it is impossible to go through a forecast without talking about it. Below are pictures showing the depth of the buried “facet crust sandwich” weak layer that was the culprit for Sundays Easter Avalanche Cycle. Test results this week have showed low to moderate propagation on this layer.  Any additional loading will activate the persistent slab problem again.

Weather
Sat, April 10th, 2021

HP received a trace of snow overnight. Temperatures have remained very cold this week remaining in the single digits and teens. Temps are -7ºF at 3505′ at 7am this morning. Since Thursday, the high at 4500′ has been 13ºF and the low -7º F. Winds have been calm to light out of the East with light to moderate gusts from the east at 4500′ since Thursday. Today wind will be 1-7mph from the east at 3000′.

Clouds will move into HP today with no significant snowfall in this next pulse of weather. However, winds are expected to increase from the Southeast up to 25 mph Sunday increasing to 45 mph Monday morning.  Another storm will be on the heels of this event, potentially bringing more moisture mid-week, but it is too far out to be confident at this point.

NWS Rec Forecast here.

NWS point forecast here.

State Parks Snow Report and Motorized Access information here.

Observations
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