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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Thu, April 4th, 2019 - 7:00AM
Expires
Fri, April 5th, 2019 - 7:00AM
Forecaster
HPAC Staff
Conditions Summary

MIDWEEK SNOW AND AVALANCHE CONDITIONS SUMMARY FOR APRIL 4, 2019

It is possible for large cornices to fail naturally or for a human or dog to trigger them. Cornice-triggered avalanches have the potential to trigger larger sluffs or slab avalanches that may fail in deeper weak layers. After a week of clear skies and unseasonably warm temperatures, much colder temperatures will have the snowpack locked up under firm crusts on sunny, E to W aspects today, and human triggered avalanches will be unlikely.

There was a very active avalanche cycle last weekend. A snowboarder remote triggered a large wet slab avalanche on the SE aspect of Skyscraper at 4300’ at about 11:45 am Saturday. Debris from this slide came very close to the snowmachine trail to the west side of Hatcher Pass. A skier reported remote triggering a small wet slab avalanche on the S aspect of Hatch Peak on Sunday. Many large natural wet slab avalanches, most gouging down to ground, have been observed last weekend and early this week. The majority of these slides have been on or under S to W aspect rocky areas. No new cornice triggered avalanches have been observed this week, but cornices are weakening as temperatures increase, and are always unpredictable despite the temperature.

Hatcher Pass has received abundant sunshine, above-freezing ridge top temperatures through Tuesday, and no new precipitation this week. Shaded aspects are still harboring faceted powder, but it’s becoming more and more difficult to find. Cooler temperatures will keep the snow firm on sunny aspects today. When warmer temperatures return this weekend, corn harvesting can be found on lower angle E to W slopes at mid to upper elevations early in the day before slopes heat up. At lower elevations the snow is an impenetrable melt-freeze crust early in the morning and isothermal slop in the afternoon, causing snowmachines and skis to trench easily.

This report is a mid-week conditions update, so please be sure to check hpavalanche.org for advisories on Saturdays and follow the HPAC Facebook and Instagram for updates. Help us keep tabs on the Hatcher Pass area! If you see any avalanche activity send us an observation HERE. Thank you to everyone who has already submitted observations this season – you can see those HERE!

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Thu, April 4th, 2019
Recent Avalanches

There was a very active avalanche cycle last weekend:

  • A snowboarder remote triggered a large wet slab avalanche on the SE aspect of Skyscraper at 4300’ at about 11:45 am Saturday.  Debris from this slide came very close to the snowmachine trail to the west side of Hatcher Pass.
  • A skier reported remote triggering a small wet slab avalanche on the S aspect of Hatch Peak on Sunday.
  • Many large natural wet slab avalanches, most gouging down to ground, have been observed last weekend and early this week. The majority of these slides have been on or under S to W aspect rocky areas.
  • Many small to large natural wet loose avalanches, many gouging down to ground have been observed last weekend and early this week.  The majority of these slides have been on or under S to W aspect rocky areas.  Some of these triggered large wet loose avalanches below.
  • No new cornice triggered avalanches have been observed this week, but cornices are weakening as temperatures increase, and are always unpredictable despite the temperature.
Avalanche Problem 1
  • Cornice
    Cornice
Cornice
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.
More info at Avalanche.org

Large cornices have formed above leeward aspects and have released naturally over the last two weeks, triggering large avalanches that have stepped down and failed to ground in places. These large cornices have proven sensitive to human and dog triggers and should be avoided. Give cornices a wide berth as they can break back much further than expected and will be possible to trigger larger avalanches below. We should avoid traveling below cornices. Low visibility can make judging the size and safe route around cornices difficult. Cornices are extremely unpredictable.

Avalanche Problem 2
  • Wet Slab
    Wet Slab
Wet Slab
Wet Slab avalanches are the release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slabs can be very unpredictable and destructive.
More info at Avalanche.org

Human triggered wet slabs will be unlikely at all elevations today. Temperatures were much colder both overnight, and during the day yesterday, than the ridge top highs of up to 40 degrees last weekend. However, even at 10 am yesterday, with an ambient temperature of 27 degrees, observers noted snow plopping off of rocks warming in the sun and water trickling down rock slabs at 4500’. The forecasted high temperature at 3500’ was 29 degrees F, yet the temperature was 33 degrees F at 11 am. It won’t take much power from the sun to warm rocky areas, especially on SW to W aspects, increasing the potential for wet slab avalanches.

Stepping off your snow machine or out of your skis to see if you are sinking in past your shins is a good clue you should head to lower angle terrain or a different aspect to recreate. Wet slabs can be remotely triggered and tests can be unreliable.

Wet slabs are unlikely at the lower elevations where the snowpack structure is mostly weak, lacking a slab component. However, wet slabs at mid elevations or upper elevations may run into low elevations so beware of being in run-outs under steep E to W slopes.

Additional Concern
  • Wet Loose
    Wet Loose
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.
More info at Avalanche.org

Similar to the discussion for wet slabs, colder overnight temperatures and daytime highs will make human triggered and natural wet loose avalanches unlikely today.

This does not mean there is no danger. Small avalanches are possible in isolated areas or extreme terrain, particularly among or under rocks, SE to W aspects below 2500’, on slopes steeper than 40 degrees.

With significantly warmer temps earlier in the week, many wet loose avalanches have gouged deeply through the snowpack and some have been large enough to bury, injure, or kill a person. Wet loose avalanches have also triggered large wet slabs on SE to W aspects.

Pay attention to rollerballs gaining momentum, sinking in up to your shins in the snowpack, and watch for wet loose activity on other aspects and terrain. These are all great clues the wet avalanche hazard is rising and indicators that it’s time to move to shadier and less saturated slopes to travel on. We should avoid traveling over or in terrain traps, as they amplify the consequence of even a small slide.

Weather
Thu, April 4th, 2019

Weather at 3450′ since Saturday 3/30:

Temperatures averaged 31°F, with a low of 16°F and a high of 47°F.

Winds averaged N 4 mph, max 9 mph.  Max gusts recorded were N 13 mph .

There has been no new snow recorded at Independence Mine.

Weather at 4500′ since Saturday 3/30:

Temperatures averaged  29°F, with a low of  14°F and a high of 40°F.

Winds averaged ENE-ESE 4 mph, max 16 mph.  Gusts averaged E 9 mph, max gust 36 mph.

Forecast Weather

Stay tuned to the NOAA point forecast for an updated weather forecast each day. The best way to see if it’s snowing in Hatcher Pass is to look at the webcam snow stake HERE and the Independence Mine SNOTEL site HERE

State Parks Snow Report and Motorized Access information can be found here.

Observations
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