Avalanche Advisory, Saturday, February 4, 2017 at 7am

Issued: Sat, Feb 04, 2017 at 7AM

Expires: Sun, Feb 05, 2017

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Above 3,500ft Moderate

2,500 to 3,500ft Moderate

Below 2,500ft Low

Degrees of Avalanche Danger ?

1. Low
2. Moderate
3. Considerable
4. High
5. Extreme

Avalanche Danger Rose ?

Avalanche Problems ?

Problem Details

A higher tracking pyroclastic star, warm temperatures, and winds have highlighted this week at HP. Friday’s warm up felt like spring knocking on the door. Roller balls ran on southern aspects all the way to upper elevations on southern slopes with high angles of incidence. The persistent slab avalanche problem has improved, only enough to lessen the likelihood of triggering an avalanche, but not removing the possibility of triggering a high consequence avalanche.

A 4-5″ blanket of soft, low density powder over varying surfaces has made for good powder riding and skiing. In some locations, the base is completely sugar and rotten, making snowmachine riding interesting. While the number of recent human triggered avalanches has drastically dropped, a recent human triggered avalanche on the Willow side reminds us that it is still possible to trigger avalanches that can bury, injure, or kill.


AVALANCHE PROBLEM: PERSISTENT SLAB

The persistent slab avalanche problem, related to the basal, persistent weak layer, has a moderate hazard at upper and mid elevations, on all aspects, on slopes 35° and steeper, for slabs 1-3′ deep, up to D2 in size, and low hazard at low elevations.

Travel advice: Heightened avalanche danger on specific terrain features. Identify features of concern and evaluate snow and terrain carefully.

The probability of triggering a slab avalanche has decreased this week as the snowpack has had time to adjust to January 25-26’s severe wind load and subsequent avalanche cycle. While the snowpack has adjusted, the problem has not been removed. Natural and human triggered avalanches are not likely, however it will be possible to human trigger slab avalanches in specific locations. The persistent slab will be stubborn to trigger.  This is a low probability, high consequence hazard.

Predicting these locations may be difficult, but will tend to be concentrated in areas that received previous wind loading since Jan 25. These winds generally loaded West to Northeast aspects, however this problem is not limited to these spects alone. The snowpack may let you get away with steep skiing and riding, however, do not underestimate the hazard, or allow the absence of recent avalanches lull you into complacency. The evidence is there, the possibility exists, and the snowpack dragon just needs people in the equation for it to be a problem. This type of avalanche problem may be capable of allowing multiple people to travel on a slope before failing.

Specific areas, such as the leeward side of mountain passes and upper elevation ridgelines, hold the highest likelihood for human triggered avalanches. Pay close attention, and use careful visual inspection, to detect and avoid, old, wind loaded pillows and slopes covered by new snow, as well as new, surface clues, such as scallops and ripples. Many of these slopes have already avalanched, but there are still some that have not, which will still be possible to trigger.

Assessing the avalanche hazard will be very difficult. To offset this difficulty, adding margins of safety through conservative decision making and safe travel protocols will be paramount. If you choose to enter avalanche terrain, reduce your exposure, by avoiding large slopes, bowls and staring zones with terrain traps. Be prepared, and do not lower your guard. Use excellent travel protocol, ride and ski one at a time through avalanche terrain, and use safe zones. Every person in your group should be carrying a beacon, shovel, and probe on your person, and know how to use them. Great snow conditions exist and can be enjoyed without the looming hazard on slopes 25° and less steep, and outside of the runnout of steeper slopes from above.

Avoid wind loaded areas where stiff snow sits over weaker snow.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

A rotten snowpack with a stiff slab sitting over weak basal facets.

Video: Independence Mine 3100′

 

 

Recent Avalanche Activity

The only human triggered avalanche reported this week was on the Willow side. A snowboarder triggered an avalanche near Hidden Bowl, around 4400′, on a steep wind loaded slope. The avalanche failed near the ground on the basal facets and entrained some morainal rock and large boulders. The rider was able to outrun the avalanche and escape into a safe zone. The debris was capable of burying, injuring or killing a person. This avalanche is consistent with instability tests, indicating that the basal facets are still capable of producing human triggered avalanches in specific areas.

Feb 2, 2017 – Near Hidden Bowl, Human Triggered persistent slab avalanche. No one caught.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Below: Spring is on the way

Martin Mine, IMB, upper elevation south aspects feeling the heat of the sun and producing roller balls. Spring is nearing.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Recent Weather

This week’s weather at 3550′:

4 inches of new snow and .3 inches of water accumulated on 1/29.

This week’s weather at 4500′:

Temperatures averaged 19 deg. F.

Winds averaged 7 mph, with gusts averaging 14 mph ESE. Winds picked up with gusts in the 30-40’s mph on 1/30- 31.


THE HATCHER PASS MOUNTAIN FORECAST COVERS THE MOUNTAINS IN THE
HATCHER PASS RECREATION AREA.

THIS FORECAST IS FOR USE IN SNOW SAFETY ACTIVITIES AND EMERGENCY
MANAGEMENT.

                   TONIGHT      SAT

TEMP AT 1000`      20-29 F      33 F

TEMP AT 3000`      41 F         41 F

CHANCE OF PRECIP   0%           0%

PRECIP AMOUNT
(ABOVE 1000 FT)    0.00 IN      0.00 IN

SNOW AMOUNT
(ABOVE 1000 FT)    0 IN         0 IN

SNOW LEVEL         SEA LEVEL    SEA LEVEL

WIND 3000` RIDGES  NE 10-20 MPH NE 5-15 MPH


Link to AK State Parks Snow Report for HP

HP Winter Rec. Report 1-31-17

Additional Info & Media

The avalanche hazard will be slow to improve over time, and the snowpack will  continue to be sensitive to rapid weather changes. Temperature spikes, wind loading and precipitation will have the ability to increase the avalanche hazard quickly.

A blocking pattern of high pressure over mainland Alaska is forecasted to last through the end of the week, with the next chance for snow around next Friday and into next weekend. A gentle outflow pattern is forecasted through the weekend with light Northerly winds.

NWS Recreational Forecast for Hatcher Pass here.

Posted in HPAC Forecasts.
Jed Workman

Forecaster: Jed Workman