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, January 5th, 2019 - 7:00AM
Expires
Sun, January 6th, 2019 - 7:00AM
Forecaster
HPAC Staff
The Bottom Line

Today a MODERATE avalanche hazard for persistent slab and loose dry avalanches exists. Human triggered avalanches are possible and natural avalanches are unlikely.

Slab avalanches are the main concern, up to 2-4 feet deep (consistent with the depth of the snowpack), and large enough to bury, injure, or kill a person.

We can not emphasize this enough, AVOID STEEP SLOPES WITH TERRAIN TRAPS; choose slopes with gentle, fanning runouts.

Thanks to our sponsors.
Sat, January 5th, 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

Remotely triggered, natural, and human triggered avalanches were reported on 12/30. These avalanches occurred as a result of high winds. See more information HERE.

No other avalanches have been reported.

Avalanche Problem 1
  • Persistent Slabs
    Persistent Slabs
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.
More info at Avalanche.org

A recent round of strong, Southeast winds earlier in the week, wind loaded leeward aspects, generally West to North, tipping the balance and resulting in some natural and human triggered avalanche activity. The snowpack has now adjusted to this new load. The last natural avalanche observed was around December 30-31, during the 12/30-1/2 wind event.

The good news is stability has generally been on the healing trend, albeit a very slow trend. The bad news is, weak layers in the snowpack will not be going away anytime soon, and will continue to be problematic.

Today human triggered slab avalanches will be possible at mid to upper elevations, on all aspects, up to 2-4 feet deep, on slopes 35º and steeper.  Remotely triggered avalanches may be possible in isolated locations, more likely, but not limited to, upper elevations. Expect slab avalanches to be much deeper, and therefore more consequential, on previously wind loaded, leeward aspects and features, generally West to North.

A number of weak layers exist in the snowpack, but we are currently most concerned about two in particular.

  • Basal facets. These are surrounding an old melt-freeze crust that is degenerating into a pile of soft, fist hard facets at the ground.
  • Buried surface hoar. This is located near a thin, fragile rain crust, deep in the snowpack, in a difficult to predict, patchy distribution.

Video below from January 4, 2019: Snowpit instability test results on the persistent slab problem Marmot Mountain, W, 3800′, 41º slope. Basal facets require a lot of force to trigger, but when they do propagation results are alarming.

[Pit in video shows results representative for the area: Moderate to strong strength, poor structure, and high propagation.]

Avalanche Problem 2
  • Dry Loose
    Dry Loose
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.
More info at Avalanche.org

Loose dry avalanches will generally be possible to trigger on all aspects, on slopes 35º and steeper, at mid to upper elevations. Approximately 8-10″ of low density snow is sitting on smooth, firm surfaces. Triggering a loose dry avalanche will be uneventful in most circumstances, however, it may be possible to be caught and carried by this avalanche problem into greater hazards such as terrain traps, which will compound the risk and make this hazard very real.

Weather
Sat, January 5th, 2019

This week’s weather at 3550′:

Temps averaged 20ºF, with a low of 8ºF and a high of 34ºF.

IM reported 10″ of new snow.

Overnight at 3550′:

Temps averaged 13°F.

No new snow.

This week’s weather at 4500′:

Temps averaged 16ºF, with a low of 5ºF and a high of 26ºF.

Winds averaged SE 11 mph, max 43 mph . Gusts averaged SE 19 mph, max gust SE 56 mph.

Overnight at 4500′:

Temps averaged  12ºF overnight, with a Low of 9ºF.

Winds averaged SE 3 mph overnight. Max gust E 7 mph.


NWS Rec Forecast HERE


State Parks Snow Report and Motorized Access information HERE


TREND

HP’s weak snowpack will persist for a very long time. Pay attention to weather changes as our snowpack will not like rapid change. Each time our snowpack is rapidly loaded with new snow, or wind transported snow, expect the avalanche hazard to rise. Each time the weather becomes mild and boring, expect the snowpack’s stability to slowly increase.

This weekend the forecast is calling for light winds and cool temps. This kind of weather will not increase the avalanche hazard. However, pay close attention to the winds. For Sunday and into Monday, models are suggesting a slight increase in the pressure differential between mainland Alaska and the Southcentral coastline. This is not predicted to increase winds speeds over the next couple days. However, if the pressure differential were to build beyond the forecast, strong, outflow winds could increase in the avalanche hazard.

.

Observations
Recent Observations for Hatcher Pass