Hatcher Pass Avalanche Center
Hatcher Pass

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ARCHIVED - Forecasts expire after 24 hours.
Issued
Thu, March 9th, 2023 - 7:00AM
Expires
Fri, March 10th, 2023 - 7:00AM
Forecaster
Jake Kayes
Avalanche risk The Bottom Line

The sudden spring like temperatures are finally over. A major shift in weather will occur today with cooler weather and strong north winds affecting the forecast area today thru Saturday.

Today the avalanche danger is MODERATE at all elevations on southeast thru southwest aspects on slopes 35 degrees and steeper. 

Human triggered Persistent slab avalanches 4 to 12 inches thick are possible. These avalanches will be small to large in size.

Human triggered wind slabs will be possible at upper elevation on southerly aspects by the afternoon. These avalanches will be small to large in size.

Natural avalanches are unlikely.

Riding conditions have deteriorated due to the warm weather. Expect firm surfaces and poor riding on southerly aspects.

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Thu, March 9th, 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

Warm temps for the last 2 and half days with temps reaching 46ºF at 4500’ caused numerous natural slabs and large wet loose avalanches. 

Natural persistent slab avalanche, right of president’s ridge South aspect 3100′

3.8 Natural slab Lodge run on Marmot 4000′ SSW

3.7 Wet loose debris on Marmot 4500′ SSW

3.8 Wet loose skyscraper with some debris touching summer road. 4000′ S aspect

 

Avalanche Problem 1
  • 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

Small to large human-triggered persistent slab avalanches are possible at all elevations on Southeast thru Southwest aspects on slopes 35 degrees or steeper. Natural avalanches are unlikely. 

This week the forecast area had unseasonably warm temperatures and did not go below freezing for two and a half days. More than one night above freezing is typically a red flag for avalanches. These warm temps were due to a strong inversion that began on the morning of March 6th above 2500’. During this warm-up Independence Mine reached 45ºF and Marmot reached 46ºF. 

Snow surfaces began to melt on steep slopes on southeast thru west aspects. These warm temperatures weakened the facet crust combo 4-12 inches beneath the surface that was responsible for several human-triggered avalanches last week and weekend. 

Human triggered persistent slab avalanches March 4th. The facet/crust combo was already sensitive before the big warmup.

Temperatures finally went below freezing last night at all elevations. Marmot 4500’ had a low of 20ºF and Independence Mine had a low of 21ºF.  This will begin to slowly improve stability and cause snow surfaces to freeze. Expect crusts and firm surfaces on Southeast thru West Aspects. 

To identify this avalanche problem look use hand pits, pole probes, and stability tests. Look for weak-faceted snow, sitting on top of a sun crust 4-12 inches below the surface. Shooting cracks and collapsing will be red flags for this problem. 

As always use safe travel techniques if you decide to travel in avalanche terrain. This means spreading out when ascending, traveling downhill one at a time, and regrouping out of the runout of avalanches.

 

Avalanche Problem 2
  • 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

Strong to extreme winds from the North with gusts up to 31mph are forecasted to affect Hatcher Pass today thru Saturday. These winds will be capable of transporting low-density snow and creating wind slabs later in the day on southerly aspects. These wind slabs will be small to large in size and found near ridge top and leeward features. These slabs will continue to build on Friday. 

There is some uncertainty in timing and intensity of winds.

Look for signs of blowing snow, and flagging/plumes at ridgetops. Smooth lensed shaped features and hollow drum like sounding snow are signs that wind slabs have formed.

Weather
Thu, March 9th, 2023

From the AVG Discussion:

Weather conditions shift towards high winds as a trough sinks southward across Southcentral late this evening. Cold air will advect through the area behind the trough and promote strong, gusty winds from the northeast. Not only will these winds channel through gaps, they will also be very strong along ridge tops. There is less certainty with the strength and peak timing of the winds further west along Cook Inlet and Hatcher Pass. Winds will begin to ramp up this evening and are expected to peak Friday morning. Near Hatcher Pass, winds are likely to reach 60 mph, but could top out around 75 mph. Higher confidence remains farther east over the eastern Chugach Mountains. Widespread ridge top winds will likely be in the 70 mph range, but the potential for 85 mph is possible throughout all of Friday morning and into the afternoon. Winds will remain strong through Saturday morning as winds very gradually decrease.

Independence Mine 3550′ March 4-9th

Marmot 4500′ Mar 4-9th

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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