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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Sat, March 23rd, 2019 - 7:00AM
Expires
Sun, March 24th, 2019 - 7:00AM
Forecaster
HPAC Staff
The Bottom Line

The avalanche danger is Moderate today in the morning for Wet Avalanches at mid and low elevation. Danger will rise to Considerable for Wet Avalanches at mid and low elevation on steep SE to SW aspects in the afternoon and into tomorrow if we continue to see above freezing temperatures overnight.

Cornices are huge and sensitive and will be possible for a human or dog to trigger today. Cornices will have the potential to trigger larger sluffs or slab avalanches that may fail to the ground.

Record high temps have thrown the snowpack into a spring cycle. Timing will be key to finding enjoyable skiing/riding and avoiding avalanches today. Early bird gets the worm!

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Sat, March 23rd, 2019
Upper Elevation
Above 3,500'
Considerable (3)
Avalanche risk
Mid Elevation
2,500'-3,500'
Considerable (3)
Avalanche risk
Low Elevation
Below 2,500'
Moderate (2)
Avalanche risk
Upper Elevation
Above 3,500'
Avalanche risk
Considerable (3)
Mid Elevation
2,500'-3,500'
Avalanche risk
Considerable (3)
Low Elevation
Below 2,500'
Avalanche risk
Moderate (2)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Recent Avalanches

Numerous natural and human triggered wet-loose avalanches were observed most of the week. Most wet-loose were small in size, in terrain 40° and steeper, and on ALL aspects, and all elevations. The largest avalanches were up to D1.5 in size and on SE to SW aspects.

A notable cornice fall on 3/21 (triggered by a dog) triggered the persistent slab on a NW aspect at 4500’ on 3/21. The pocket failed to the ground and was D1.5. The dog is reported to be fine.

For more info and pictures on the Natural and Human triggered avalanches this week , check out the mid week summary, HERE or weekly OBSERVATIONS HERE.









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

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

This past week of unruly warm weather has thrown hatcher pass into a wet-avalanche cycle. Mostly small wet-loose sluffs will be possible on steep slopes, on mostly SE to SW aspects in the morning, at mid and low elevation.  Avalanche activity will rise to considerable, human triggered likely, naturals possible, at mid and low elevation in the afternoon, on steep slopes, mostly SE to SW aspects.  We are right at the tipping point of seeing more frequent and larger wet avalanches, up to D2 in size.

The good news: Wet loose avalanches are predictable and avoidable. Timing is everything. The bad news: Spring appears to be here a month early and it is not freezing below 3000’ at night.  

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. This may mean you are left with some light at the end of the day, temps will be comfortable outdoors, so head to the car for a tailgate party instead of pushing this hazard too far.


Above: 3/19 ,Wet loose avalanches.  Microdot, 4500′, S aspect.



Above: 3/20 or 3/22, Natural wet-loose, SW aspect Skyscraper, 3900′.


More about wet avalanches in the avalanche problem toolbox, HERE.

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

With 3 nights of temperatures above freezing at 3000’ and below, the wet-slab hazard may rise today in the afternoon at mid-elevation, on SE to SW aspects, on slopes 40° and steeper. Wet slabs are hard to predict. Wet slabs are becoming more and more likely to occur with this warm weather trend at mid elevation where the snowpack structure is shallower, and has a slab sitting on crusts over weak basal facets and depth hoar.  If temperatures continue to increase this weekend, wet slabs may increase from a moderate to considerable danger in the above mentioned locations.  Wet-slabs could be up to D2 is size, or large enough to bury, injure, or kill a person. 

Paying attention to rising temperatures, and lack of overnight freezing are your best red flags for knowing when wet-slabs will occur. Wet-slabs can be remotely triggered and tests can be unreliable.

Wet slabs are unlikely at the upper elevations where temperatures have remained cool overnight, and at the lower elevations where the snowpack structure is mostly weak, lacking a slab component.

Avalanche Problem 3
  • 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 earlier in the week continued to build large cornices that have proven sensitive to human triggers.  3 known sizeable cornice fall events have occured in the past week, including two humans and one dog. All cornice falls triggered avalanches up to D1.5 in size. Let’s remind ourselves that cornices often break farther back than expected. 4 people and 1 dog passed by on the same skin track, nearly 20’ back from a cornice before the 2nd dog triggered the 15′ cornice chunk, leading to a D1.5 persistent slab avalanche. Picture HERE or FB post here

Low visibility can make judging the size and safe route around cornices difficult. Cornices are extremely unpredictable. Cornices are too large to try to intentionally trigger.  Give cornices a wide berth as they can break back much further than expected and will be possible to trigger larger avalanches below. Avoidance is the best mitigation tactic. Minimize your time spent under or near cornices.

 

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) and LARGE cornices.

 

 

 

Weather
Sat, March 23rd, 2019

This week’s weather at Independence Mine 3550′:  OLD

Temps averaged 36ºF, with a low of 19ºF and a high of 42ºF.

IM recorded 4” of new snow and .4″ water (SWE) this week.  

Overnight at 3550′:

Temps averaged 36°F.

No new snow.

This week’s weather at Marmot Weather Station 4500′:

Temps averaged 27ºF, with a low of 14ºF and a high of 35ºF.

Winds averaged ESE 11 mph, max 26 mph . Gusts averaged ESE 19 mph, max gust ESE 53 mph.

Overnight at 4500′:

Temps averaged 31ºF overnight.

Winds averaged E 31 mph overnight. Max gust E 15 mph.


NWS Rec Forecast HERE


NWS point forecast HERE


State Parks Snow Report and Motorized Access information HERE


TREND    

Expect warmer temperatures, some clouds and/or scattered snow showers, and winds E 3-12 mph today  at 3000′. Avalanche danger will remain the same until temperatures increase again. If we continue to see temps above freezing up to 3000’ overnight, expect wet-avalanches at mid and low elevation to be likely.  

Observations
Recent Observations for Hatcher Pass