Hatcher Pass Avalanche Center

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Sat, April 3rd, 2021 - 7:00AM
Expires
Sun, April 4th, 2021 - 7:00AM
Forecaster
Allie Barker
The Bottom Line

The avalanche danger is CONSIDERABLE today and could RISE to HIGH this evening through Sunday as a huge storm is expected to deposit 18″ to 28″ inches of snow thru Sunday evening . It will be LIKELY to HUMAN TRIGGER AVALANCHES today on all aspects, at all elevations.  Several human triggered avalanches were reported on Thursday and Friday, large enough to bury, injure, or kill a person. Dangerous conditions exist. Careful snowpack evaluation, cautious route finding, and conservative decision making are essential.  Stay safe, stay informed and spread the message.

 

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Sat, April 3rd, 2021
Upper Elevation
Above 3,500'
Considerable (3)
Avalanche risk
Mid Elevation
2,500'-3,500'
Considerable (3)
Avalanche risk
Low Elevation
Below 2,500'
Considerable (3)
Avalanche risk
Upper Elevation
Above 3,500'
Avalanche risk
Considerable (3)
Mid Elevation
2,500'-3,500'
Avalanche risk
Considerable (3)
Low Elevation
Below 2,500'
Avalanche risk
Considerable (3)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Recent Avalanches

Numerous human triggered avalanches have occurred since Thursday. For avalanches earlier in the week, check out the conditions summary HERE.

 

Near the Punk Spines, remotely triggered persistent slab 4/1

Near the Punk Spines, remotely triggered persistent slab NW, 3000′, 4/1

 

Skier triggered large avalanche , Arkose Ridge approx 3800′ and wraps the ridge from SW to NE aspects. 4/2

 

Same picture as above from a different angle. 4/2

 

4/2 Powderblast from a large avalanche on Arkose Ridge on the south side of the Little Su at approx Mile 10.photo credit: Skeetawk

 

4/2 Bullion Mtn SE aspect 4500′, remote triggered by snogo (unverified). Look at the wide propagating crown!

 

4/1 Moose Creek near Dnigi Hut, Snogo triggered or remote , W aspect, 4000′ . Apparently, this is the smaller of two avalanches that was triggered that day!

 

Human triggered persistent slab near Gold Chord Lake, SW 3900′ 4/2

 

Avalanche Problem 1
  • Persistent Slabs
    Persistent Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
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.

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

Saturday morning: Persistent slabs up to 18″ deep will be likely to trigger today on all aspects, at all elevations. Persistent slabs are sitting on a widespread weak sugary faceted layer on top of a widespread sun crust/drizzle crust combo in many locations at Hatcher Pass. New snow from last Sunday and Monday blankets the terrain.  This problem will NOT be obvious to detect today with the lure of good snow quality.  The slab is present on all East to South to West aspects and in specific locations on Northerly aspects.  The bed surface varies from a sun crust/drizzle crust on East to South to West aspects, to a buried drizzle crust on Northerly aspects. The key take away is that the current hazard is already elevated with slab avalanche problems and will be exacerbated with a new load.  Cracking and whumping are being reported from nearly all users, and the snowpack is touchy.

This is an unusual set up for Hatcher Pass for April. Unfortunately this problem is not going away and will likely get worse before it gets better.

Saturday afternoon through Sunday: A major storm is expected to dump on Hatcher Pass with 18″ to 28″ inches of moist snow and moderate to strong winds starting Saturday afternoon/evening through Sunday. Any additional load on the current snowpack will increase the likelihood for triggering an avalanche, and the depth and size of the avalanche, on all aspects, at all elevations. If this storm produces, the snowpack will reach a tipping point. Expect avalanches to fail 2 to 3 feet deep in the deeper facets and depth hoar on East to South to West aspects and 18″ to 2 feet deep on North aspects. Don’t think you can outsmart an avalanche. The mountains don’t care who you are.  Route finding to stay safe in avalanche terrain in these conditions will be very challenging.  We anticipate the avalanche danger to rise to HIGH on Sunday. Very dangerous conditions exist. Travel in avalanche terrain is not recommended this weekend.

 

 

4/2 PST photo showing the slab on a west aspect that has propagated and failed on facets on the sun/drizzle crust on a west aspect at 3600′. This is the culprit weak layer for all the avalanches this week and will be easily overloaded with any additional snow this weekend.

 

Avalanche Problem 2
  • Dry Loose
    Dry Loose
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
Dry Loose
Dry Loose avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.

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 to Large Dry Loose sluffs will be likely to trigger in the afternoon through Sunday if the storm deposits 6″ of snow or more. Warm weather will bring moist snow which will easily sluff and entrain deeper weak sugary snow, on steep slopes above 40º on all aspects, at all elevations. This hazard will increase as the storm intensifies. Getting sluffed into a terrain trap will increase the size and consequence of any avalanche.

Weather
Sat, April 3rd, 2021

Light snow is expected to develop late Saturday morning into early afternoon. Snow will then intensify Saturday afternoon and evening as low level upslope flow continues to strengthen ahead of the front. Heavy snow and strong winds are expected Saturday evening through Sunday. Snow will diminish Sunday afternoon through evening as the trough and surface front exit eastward. Colder and drier air will quickly move in Sunday night through Monday.

The Hatcher Pass Mountain Forecast covers the mountains in the
Hatcher Pass Recreation Area.

This forecast is for use in snow safety activities and emergency
management.
              Today        Tonight

Temp at 1000`      25-32 F      25 F

Temp at 3000`      16-22 F      20-26 F

Chance of precip   90%          100%

Precip amount
(above 1000 FT)    0.24 in      0.70 in

Snow amount
(above 1000 FT)    1-3 in       7-11 in

Snow level         sea level    sea level

Wind 3000` ridges  S 6-18 mph   S 12-22 mph

Remarks...Total snow accumulation of 18 to 28 inches through Sunday evening.
QPF amounts of 1.25 to 1.9 inches through Sunday evening.



 

 

 


NWS Rec Forecast here.

NWS point forecast here.

State Parks Snow Report and Motorized Access information here.

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