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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Thu, April 8th, 2021 - 7:00AM
Expires
Fri, April 9th, 2021 - 7:00AM
Forecaster
Allie Barker
Conditions Summary

Persistent slabs will be possible to human trigger today on all aspects, at all elevations today. Naturals will be unlikely.

Sunday’s historic Easter Avalanche Cycle has left its mark on Hatcher Pass with many avalanches crossing the road. DOT is waiting for the snowpack to stabilize to start clearing the road.

HP received 1-2″ of snow last night with another 1-2″ expected today. Strong to extreme northerly winds, gusting up to 50mph are expected by Thursday night. Expect strong winds to build wind slabs on southerly aspects and increase the avalanche danger.

 

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Thu, April 8th, 2021
Recent Avalanches

Numerous large and very large avalanches occurred Sunday after HP received 11″ of new moist snow with 2″ SWE (snow water equivalent) combined with moderate to strong wind gusts. 5 avalanches crossed the upper road and 1 of those also crossed the lower road between Skeetawk and Gold Mint. See more photos from the Easter Avalanche Cycle HERE.

No avalanches have been observed or reported since Sunday.

4/4 Arkose Natural , W 3600′ credit: Tim Leach

 

4/4 Natural, Arkose ,SW 3800′ credit: Tim Leach

 

4/4 Backside of Women’s Run aka Sunnyside of Gov’t , SE 3600′

 

4/4 Naturals on Government , NE 4500′

 

More avalanches from the Easter Avalanche Cycle

 

4/4 Natural on the Sunnyside of Government , ESE 3600′

 

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

Persistent slabs, 2′ to 3′ deep, will be possible to human trigger today on all aspects, at all elevations today. Naturals are unlikely.  The infamous “facet-sun crust-drizzle crust-facet sandwich” weak layer is now buried deeper in the snowpack after Sunday’s storm. Most avalanches in the Easter Avalanche cycle failed on this layer.

Cold temps Monday through Wednesday have assisted this new slab in losing density or its “slab like character” which has resulted in moderate test results on Wednesday. However, limited information is available from upper elevation due to the road being closed.  We expect this persistent weak layer to go through periods of dormancy and activity with new snow, wind, or rapid warming for the rest of the season.

Winds are expected to pick up this evening NE 15-30 with gusts up to 50 mph. North winds will build new wind slabs on southerly aspects and likely increase the avalanche danger again.

 

 

The slab is now 2 to 3 feet thick!

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

A couple inches of new snow overnight combined with another 1-2″ today will make it possible to human trigger small dry loose sluffs in terrain steeper than 40º on all aspects and all elevations today. Any new crusts will act as a good sliding bed surface for new snow.

Weather
Thu, April 8th, 2021

Sunday brought 11″ of new moist snow with 2″ SWE and 20 to 40mph wind gusts from the SSW, SSE, back to the W for over 24 hours. This historic Easter Avalanche cycle left its mark on HP. Many storm slabs, shallow wind slabs, and large to very large persistent slabs failed with 5 avalanches crossing the upper road and 1 of the 5 crossing the lower road between Steetawk and Gold Mint.

Our crisp, cold winter returned on Monday through Wednesday with temps reaching a low of 2ºF at 4500′ and sustaining near single digits. Clouds moved in Wednesday night bringing 1-2″ of precipitation. Another 1-2″ of snow are expected today with winds increasing NE 15-30 mph and gusts increasing to N 50 mph by Thursday night. Clear cold temps are expected Thursday night into Friday with wind chills reaching -35ºF by Friday night. It appears that winter is far from over.


NWS Rec Forecast here.

NWS point forecast here.

State Parks Snow Report and Motorized Access information here.

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