Hatcher Pass Avalanche Center

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ARCHIVED - Forecasts expire after 24 hours.
Issued
Thu, April 6th, 2023 - 7:00AM
Expires
Fri, April 7th, 2023 - 7:00AM
Forecaster
Allie Barker
Avalanche risk The Bottom Line

The avalanche danger is MODERATE for WET LOOSE avalanches at all elevations, on SE to SW aspects, on slopes steeper than 35º.

A LOW hazard exists for PERSISTENT SLABS on northerly aspects, NW to NE, on slopes steeper than 30º.

5-6″ of new snow this week combined with high humidity and significant cloud cover have dramatically moistened snow surfaces on all aspects.

Expect stability to remain good with few avalanche problems until we see a rapid warm-up, significant loading event, and/or it ceases to freeze at night. May your Easter egg hunt include finding good riding conditions!

 

Special Announcements

Saturday, April 15th will be the last forecast of the season. We will continue to post observations throughout the spring. If you haven’t gotten a chance to donate to your favorite grassroots community avalanche center, it’s not too late. Thank you for all your support this season. Donate here.

Thu, April 6th, 2023
Upper Elevation
Above 3,500'
2 - Moderate
Avalanche risk
Mid Elevation
2,500'-3,500'
2 - Moderate
Avalanche risk
Low Elevation
Below 2,500'
2 - Moderate
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

One human triggered persistent slab was reported on April 4 on a NE aspect at 3600′ on Wimp Bowl. See obs here. No pictures were taken.

Numerous natural small to large loose dry avalanches (sluffs) were observed on Wednesday after 5-6″ of new snow in steep terrain on all aspects.

4/5 Microdot 4600′ SSW

 

4/5 Skyscraper 3800′ SE aspect

On 4/5 a loose-wet avalanche (sluff) was human triggered on the south face of Microdot and ran approximately 600 ft. See obs here.

 

same avalanche as above Microdot

 

Avalanche Problem 1
  • Wet Loose
    Wet Loose
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    Size
Wet Loose
Wet Loose avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

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

Loose Wet avalanches aka wet sluffs will be likely to trigger on southerly aspects SE to SW, at all elevations, on slopes steeper than 35º.  Significant cloud cover and high humidity over the past two days has had a major greenhousing effect on all snow surfaces.  5-6″ of new snow from 4/4-4/5 above 3500′ has already become shockingly moist on all aspects including north. Expect to find 5″+ of new moist snow on firm crusts on south aspects that will be easy to trigger and initiate a wet sluff. We observed moist snow in the morning and our party triggered a slow-to-start wet loose that gained significant momentum and ran approximately 600-800 ft.

Checking out structure on a south aspect on Microdot. The human triggered wet sluff can be seen with debris running nearly to the valley floor. 4500′ S aspect

 

Human triggered Wet sluff that occurred at 1pm on Wednesday on a south aspect on Microdot at 4500′. This sluff was slow to initiate and quickly grained momentum and has the potential to injure a person or dog.

Although temperatures at 3500′ have remained in the low twenties this week, it felt like 50ºF on Wednesday.  Don’t forget your t-shirt, skin wax and glopper stopper and leave the long underwear at home!

Wet loose sluffs can entrain a significant amount of snow as they gain momentum. They can start out as a small rollerball and easily become large enough to bury, injure, or kill. Avoid sunny or moist slopes during the heat of the day which might be most of the day with significant cloud cover.  If the slope you’re on is getting warm, sticky, or unsupportable consider moving to cooler aspects or going to the lodge for a beer.


It’s hard to believe it’s April already. As spring temperatures continue to warm up keep an eye out for these avalanche problems in the next several weeks:

  • Loose Wet avalanches becoming more likely on all aspects
  • Wet Slab avalanches as soon as nightime temps cease to freeze for 3 nights or more
  • Cornices that may break above you or trigger an avalanche below you
  • Glide cracks starting to open up and become a hazard
Avalanche Problem 2
  • Persistent Slabs
    Persistent Slabs
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    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

6″ to 12″ thick persistent slabs will be mostly unlikely but still possible to trigger in isolated and extreme terrain, on northerly aspects, NW to NE, at mid and upper elevations, on slopes 30º and steeper.

Numerous people were out recreating during the good weather spell Saturday-Monday. Most sought after fine northerly lines and no avalanches were observed or reported. However, some evidence exists which points towards the possibility of triggering a slab avalanche where persistent grains have been preserved and are sitting on firm bed surfaces. However, due to the lack of a continuous weak layer/bed surface combo, finding a spot to trigger a slab will be challenging but not impossible.

On Tuesday, a slab was human triggered on a NE aspect at 3600′ that was approximately 70′ wide, ran 80′, with a crown depth ranging from 6-12″ thick. To avoid this problem we recommend doing hand shears and pole tests to identify whether a cohesive slab exists that is sitting on a persistent grain or graupel on a firm crust.

Weather
Thu, April 6th, 2023

On 4/4-4/5 HP received 5-6″ of new snow with 0.4″ SWE at above 3550′.

This graph shows high humidity (and clouds) over the past couple days which have contributed to moistened snow surfaces.

It’s lightly snowing this morning. Expect clouds and 1-3 inches of snow throughout the day before a break the weather Friday, followed by another low pressure as we approach the weekend.


 

NWS AVG Forecast here.

NWS point forecast here.

Marmot Weather Station here.

Independence Mine Snotel here.

Frostbite Bottom Snotel here.

State Parks Snow Report and Motorized Access information here.

XC trail grooming report for Mat-Su, Anchorage, and Kenai here.

Observations
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