Hatcher Pass Avalanche Center

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Thu, March 21st, 2019 - 7:00AM
Expires
Fri, March 22nd, 2019 - 7:00AM
Forecaster
HPAC Staff
The Bottom Line

This information is a Conditions Update. Danger ratings are only issued with avalanches advisories.  The next avalanche advisory is scheduled for Saturday March 23, 2019.

Previous avalanche advisories HERE

MIDWEEK SNOW AND AVALANCHE CONDITIONS SUMMARY FOR MARCH 21, 2019

Human-triggered wet loose avalanches will be likely and natural avalanches will be possible on all aspects and at all elevations.  Wet loose avalanches will be larger on solar aspects.  Human-triggered wind slab avalanches will be possible and natural wind slab avalanches will be unlikely, at upper elevations, on W to N aspects.  It may be possible, but is generally unlikely, to trigger an avalanche on deeper persistent weak layers.

Happy spring equinox everyone!  Unseasonably warm temperatures have reached summit elevations in Hatcher Pass since early Wednesday morning, and as we turn the corner into spring, it’s time to start paying more attention to warming.  Rollerballs and especially sinking in deeply in your skis or snow machine are signs that the hazard for wet avalanche activity is increasing.  Even small wet loose avalanches can have high consequences if you end up in a terrain trap.

Hatcher Pass received 4″ new snow (0.4” SWE) overnight Monday. The 4″ of snow fell during light winds, but the skiing and riding quality was immediately impacted by warming from the sun on Tuesday and above-freezing temperatures since Wednesday.  Snow has since been redistributed across Hatcher Pass due to E to ESE moderate winds gusting to strong and extreme yesterday.

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 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, March 21st, 2019
Upper Elevation
Above 3,500'
No Rating (0)
Avalanche risk
Mid Elevation
2,500'-3,500'
No Rating (0)
Avalanche risk
Low Elevation
Below 2,500'
No Rating (0)
Avalanche risk
Upper Elevation
Above 3,500'
Avalanche risk
No Rating (0)
Mid Elevation
2,500'-3,500'
Avalanche risk
No Rating (0)
Low Elevation
Below 2,500'
Avalanche risk
No Rating (0)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Recent Avalanches

Above: Wet loose avalanches, Tuesday March 19.  Microdot, 4500′, SW aspect.

Above: Large cornice-fall triggered avalanche occurred March 17.  Rae Wallace Chutes, 4500′, N aspect.

 

Above: Closer view of the crown of avalanche shown above.

 

Above: Looking down Rae Wallace Chutes towards debris pile of cornice-fall triggered avalanche from March 17th.

 

Above: Wet loose avalanches on north aspect of Hatch Peak ridgeline observed Wednesday March 20.  4000′.

 

Avalanche Problem 1
  • 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

Above-freezing temps to 4500’ since 7:00 am yesterday combined with average temps above freezing for 4 days at 3450′, and periods of sunshine today will contribute to wet-loose activity on steep slopes on all aspects and at all elevations, but particularly elevations below 3500’.  Human triggered avalanches will be likely and natural avalanches possible.  Wet loose avalanches will mostly be small, but on aspects that receive direct sun, southeast to southwest, some of these avalanches may be large enough to bury or injure a person.  Note that widespread small natural wet loose avalanches were observed even on north aspects yesterday.

A soft melt-freeze crust is sitting under Tuesday’s new snow.  This crust varies in thickness and strength with elevation and aspect. Watch this crust carefully. Once the crust melts, there will be plenty of eager facets, persistently waiting under the crust to contribute to the avalanche problem, increasing the size and consequence of any wet-loose avalanche.

 

Deeply gouging wet loose avalanche observed on Tuesday March 19.  Skyscraper Mountain, 4000′, S Aspect.

Above: Natural wet-loose at low elevation on the road cut, 3/20.

 

Avalanche Problem 2
  • Wind Slabs
    Wind Slabs
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.
More info at Avalanche.org

East and East-Southeast moderate winds gusting strong to extreme yesterday and last night have formed fresh wind slabs 6-10” thick in leeward and cross-loaded terrain, on predominantly W to N aspects.  Human-triggered wind slab avalanches will be possible and natural wind slabs will be unlikely in upper elevations. These avalanches will be mostly small, but isolated pockets, particularly in extreme terrain could be large enough to bury, injure, or kill a person.

Warm temperatures should allow this avalanche problem to heal relatively quickly.  Pole tests can easily reveal stiffer snow sitting over weaker snow and can be a good indicator for the presence of wind slabs and slab thickness.  Also be on the lookout for very stiff, hollow sounding or drum-like snow.

 

 

Large plumes of blowing snow were observed at ridgetops on Wednesday March 20.  Also note wet loose avalanches on this north aspect.

Avalanche Problem 3
  • 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

It will be generally unlikely, but may be possible to trigger an avalanche on deeper, buried persistent weak layers, SW to NE aspects, in mid to upper elevations, on slopes steeper than 35 degrees.  Particularly suspect are areas where the snowpack is thinner and weaker, such as cross loaded gullies and places where it has previously avalanched.  These avalanches may be large enough to bury, injure, or kill a person.

Additional Concern
  • 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

Moderate to strong winds have built large cornices that have proven sensitive to human triggers.  Low visibility has made it extremely challenging to see a cornices real magnitude and danger which could increase the likelihood of stepping out too far on an overhung cornice. Give cornices a wide berth as they can break back much further back then they appear and cornices can trigger larger avalanches below.  Cornices are extremely unpredictable.  It’s best to just avoid them, and minimize your exposure time to minimize your risk, especially on the ascent.

Cornices have grown large and have shown to be sensitive to human triggers in the last week.

Weather
Thu, March 21st, 2019

Weather History

Weather at 3450′ since Saturday 3/16:

Temperatures averaged 31°F, with a low of 19°F and a high of 42°F.

Winds averaged S 3 mph, max 13 mph.  Max gusts recorded were S 39 mph .

There has been 4″ new snow recorded at Independence Mine since 3/16.

Weather at 4500′ since Saturday 3/16:

Temperatures averaged  26°F, with a low of  14°F and a high of 35°F.

Winds averaged SE-ESE 13 mph, max 30 mph.  Gusts averaged SE-ESE 23 mph, max gust 57 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
Recent Observations for Hatcher Pass