Hatcher Pass Avalanche Center

Hatcher Pass Avalanche Forecast RSS

Archives
ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Sat, November 30th, 2019 - 7:00AM
Expires
Sun, December 1st, 2019 - 7:00AM
Forecaster
HPAC Staff
The Bottom Line

Natural avalanches are unlikely today and human triggered Storm Slab and Winds Slab avalanches are possible to human trigger, up to D2 in size, 1-3 feet deep, at mid to upper elevations on all aspects, on slopes 35° and steeper. Glide avalanches can release at any time, up to D2 in size.

The Thanksgiving Storm almost doubled our snowpack depth, producing approximately 30″ of snow in 3.2″ of SWE at 3500′ with larger snow totals likely at the upper most elevations.

Strong winds persisted throughout the storm, transporting abundant snow, building drifts and wind slabs up to 3 feet deep on leeward aspects at mid to upper elevations.

Temperatures at 3000′ were at or just above freezing. This resulted in rain and heavy snow up to 3000′, and dry snow above that.

The most impressive avalanches were on the SE face of Marmot at approximately 3200′, with wet slab debris making it within 20 feet of the road.

This major weather event resulted in numerous natural avalanches at the mid to upper elevations, on all aspects, during and just after the storm. The peak of avalanche activity is behind us, stability is increasing, however there is still the chance for human triggering storm slabs and winds slabs. Stability increased substantially on Friday, and we expect this trend to continue through the weekend.

At low elevation, generally lacking in snow, we now have a good base, with heavy, wet snow folding over alders and making the 16 mile road runs navigable. The avalanche hazard in the lower elevations will remain Low.

 

Special Announcements

December 5th, 6-8pm, Read the Terrain with HPAC at Black Diamond’s retail store in Anchorage.

December 6th, Safety Chat at Fish Creek Sales, 6-8pm in Wasilla.

Your community funded avalanche center needs your support. Please donate today.

 

Thanks to our sponsors.
Sat, November 30th, 2019
Upper Elevation
Above 3,500'
Moderate (2)
Avalanche risk
Mid Elevation
2,500'-3,500'
Moderate (2)
Avalanche risk
Low Elevation
Below 2,500'
Low (1)
Avalanche risk
Upper Elevation
Above 3,500'
Avalanche risk
Moderate (2)
Mid Elevation
2,500'-3,500'
Avalanche risk
Moderate (2)
Low Elevation
Below 2,500'
Avalanche risk
Low (1)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Recent Avalanches

Next 2 pictures: Two significant avalanches ran on SE side of Marmot Mountain during the Thanksgiving Storm. One in Marmot Gully One and another in Marmot Gully 2, both with debris making it very close to the road. The avalanches appear to have released mid-height in the bowls, mostly on the steeper sidewalls. The main portions of the bowls appear intact. Poor visibility has made identifying the bed surface difficult, but the Veteran’s Day Crust is suspected.

11/28/2019 – Marmot Mountain, SE, 3200′ – Debris in Marmot Gully 1 Avalanche Path coming within approximately 20 feet of the road. WS-N-D2.5-I/O

 

Close up picture of the Marmot Gully sidewalls which produced wet slab avalanches.

 

11/28/2019 – Arkose Slide Paths above the Little Susitna, near Stairstep. West, 3600-3900′,  SS-N-D2-I

 

11/28/2019 – Hatch Common Low Roll (Bennets Ridge), NNE, 3600′

 

11/28/2019 – Hatch Common Low Roll (Bennets Ridge), N, 3600′

Numerous small storm slab and/or wind slab avalanches were observed in the Rae Wallace north chutes. No pictures available.

Significant new glide cracks have recently formed on the SW face of Marmot:

Glide cracks on Marmot Mountain, SW, 4100′

Avalanche Problem 1
  • Storm Slabs
    Storm Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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
This graphic depicts how likely you are to trigger avalanches or encounter natural avalanches while traveling on avalanche prone slopes. Unlikely means that few avalanches could be triggered in avalanche terrain and natural avalanches are not expected. The chance of triggering or observing avalanches increases as we move up the scale. Certain means that humans will be able to trigger avalanches on many slopes, and natural avalanches should be expected.

Size of Avalanches
This graphic depicts the potential size and destructive force of expected avalanches. 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, large enough to bury or destroy vehicles and break a few trees, and large enough to destroy railway cars, buildings, or a substantial amount of forest. Historic avalanches are massive events capable of destroying villages and gouging or altering the landscape.
More info at Avalanche.org

Storm slabs will be possible to trigger in isolated locations, 1-3 feet deep, at mid to upper elevations. Storm slabs are present on all aspects.

With the lack of any persistent grain types at the new snow/old snow interface, we expect instabilities to be short lived and significant improvement over the next 24 hours. New snow, precipitation, and wind forecasted for today, should not significantly impact stability.

 

Avalanche Problem 2
  • Wind Slabs
    Wind Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    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
This graphic depicts how likely you are to trigger avalanches or encounter natural avalanches while traveling on avalanche prone slopes. Unlikely means that few avalanches could be triggered in avalanche terrain and natural avalanches are not expected. The chance of triggering or observing avalanches increases as we move up the scale. Certain means that humans will be able to trigger avalanches on many slopes, and natural avalanches should be expected.

Size of Avalanches
This graphic depicts the potential size and destructive force of expected avalanches. 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, large enough to bury or destroy vehicles and break a few trees, and large enough to destroy railway cars, buildings, or a substantial amount of forest. Historic avalanches are massive events capable of destroying villages and gouging or altering the landscape.
More info at Avalanche.org

Wind slabs, formed during the Thanksgiving Storm, will still be possible to human trigger today, 1-3 feet deep, located on leeward aspects, on both top loaded ridgelines and cross-loaded slopes and features, generally West to North, at mid to upper elevation. Winds were strong enough to build wind slabs not just at the top of slopes, but also mid-slope.

While West to North aspects have the heaviest wind loads, all aspects were affected by wind. A variety of wind sculpting is widespread, from large drifts to scalloping, to wind board, mixed in with few locations of non-wind effected snow.

Yesterday observers traveling on steep northerly aspects where wind loading was the most significant, found good bonding at the new/old snow interface.

Winds were strong and visibly transporting snow at upper elevation ridgelines yesterday. Winds continued to transport snow overnight and add to the wind slab problem.  Overnight winds at 4500′ were SE 10-19 mph, gusting 18-26 mph, and at 3550′ E and SE 1-8 mph, gusting 4-19 mph.

Overall we expect this avalanche problem to be improving substantially today and into tomorrow.

 

Avalanche Problem 3
  • Glide Avalanches
    Glide Avalanches
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
Glide Avalanches
Glide Avalanches are the release of the entire snow cover as a result of gliding over the ground. Glide avalanches can be composed of wet, moist, or almost entirely dry snow. They typically occur in very specific paths, where the slope is steep enough and the ground surface is relatively smooth. They are often proceeded by full depth cracks (glide cracks), though the time between the appearance of a crack and an avalanche can vary between seconds and months. Glide avalanches are unlikely to be triggered by a person, are nearly impossible to forecast, and thus pose a hazard that is extremely difficult to manage.

Likelihood of Avalanches
This graphic depicts how likely you are to trigger avalanches or encounter natural avalanches while traveling on avalanche prone slopes. Unlikely means that few avalanches could be triggered in avalanche terrain and natural avalanches are not expected. The chance of triggering or observing avalanches increases as we move up the scale. Certain means that humans will be able to trigger avalanches on many slopes, and natural avalanches should be expected.

Size of Avalanches
This graphic depicts the potential size and destructive force of expected avalanches. 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, large enough to bury or destroy vehicles and break a few trees, and large enough to destroy railway cars, buildings, or a substantial amount of forest. Historic avalanches are massive events capable of destroying villages and gouging or altering the landscape.
More info at Avalanche.org

A new glide crack on Marmot Mountain’s SW face is a reminder that this problem is still active. There is a high level of uncertainty with the timing and prediction for glide avalanche release. Avoidance is the best way to mitigate this low frequency/high consequence hazard. Avoid old glide avalanche paths which have the potential to release again. Avoid any area with glide cracks, or “brown frowns”, which can release unexpectedly.

Weather
Sat, November 30th, 2019

NWS Rec Forecast here.

NWS point forecast here.

State Parks Snow Report and Motorized Access information here.

Strong winds during the Thanksgiving Storm have made it difficult to measure new snow totals, both through weather station measurements and field observations. We are basing our best guess on the snow water equivalent from the Independence Mine Snotel data. A storm total of approximately 3.2″ of SWE roughs out to 30″ of new snow in this storm cycle. This number also seems consistent with our observations at the Marmot snow stake. Adjustments to the stake were made yesterday to account for snowdrifts blocking the view of the stake, see the latest image here.

This week at Marmot Weather Station 4500′:

Average temp 16ºF, with a high of 26ºF, low of 2ºF

Winds averaged SE 10-34 mph, gusting 17-55 mph.

This week at IM Snotel 3550′:

Average temperature 21ºF, with a high of 34ºF low of 3ºF.

Observations
Recent Observations for Hatcher Pass