Avalanche Advisory Archive 2016 – 2018

Date Issued:2017-01-05 06:50:14
Danger:1
Primary Trend:3
Primary Probability:3
Primary Likelihood:2
Primary Size:1
Primary Description:

With a taku wind event kicking off and direct loading into our urban paths avalanche danger for windslabs will be increasing.

These slabs will start quite shallow and grow in depth over time. Use extra caution in windloaded areas over the next several days.

Secondary Trend:2
Secondary Probability:5
Secondary Likelihood:1
Secondary Size:2
Secondary Description:

We have a weak layer of facets deep in the snowpack. Be aware that although hard to trigger this could be a large avalanche.

Probability of slides on this layer currently is LOW and yet we will be watching it over time as load increases. This is the type of weak layer that could last all season... and is also the type that could lead to large avalanches that could threaten the urban paths later in the season.

Discussion:

The National Weather Service Forecasts-

Today- Becoming locally windy. Mostly cloudy. Flurries. Highs around 31. North wind 10 mph. Near downtown juneau and douglas...northeast wind 15 to 25 mph with gusts to around 40 mph in the afternoon.

Tonight- Becoming locally very windy late. Mostly cloudy. Lows 18 to 26. North wind 10 to 20 mph. Near downtown juneau and douglas...northeast wind 30 mph with gusts to around 50 mph increasing to 45 mph with gusts to around 60 mph late.

Friday- Locally very windy. Mostly cloudy. Highs around 26. East wind 15 to 25 mph...except northeast 25 to 40 mph with gusts to around 65 mph near downtown juneau and douglas.

With an increase in the winds the inversion that was in place has now broken and we are seeing cooler temperatures back to summit elevations.

Temperatures had been above freezing at tram summit elevations for several days. Temperatures fell yesterday into today and this morning the tram is showing 23 degrees. This several days of warm temps allowed the snowpack to settle and bond rapidly. Now with below freezing temps in place the snowpack will be quite stable.

Temperatures are forecast to continue falling by as much as 6 degrees in the next 24 hours.

Winds this morning are light at Eaglecrest showing 6-10mph. The tram is a little higher only showing 10mph currently but forecast to increase throughout the next 24 hours.

This wind event will start to load our urban paths and increase danger throughout the wind event.

Avalanche danger is LOW at this time. As wind increases and load increase we may start to see increased danger for both natural and human triggered avalanches.

Be aware this loading will be on a multitude of bed surfaces. At lower elevations we have cold snow and surface hoar in places... this surface hoar may be found at higher elevations on Douglas Island where it remained cooler. While on the channel we may even have some areas of melt freeze with slight icy crusts to be concerned with. Danger will vary due to bed surface changes.

Danger will increase over the next 48 hours with this wind event.

Stay warm and stay safe.

Tip:

Wind Loading

The added weight of wind drifted snow.

Wind Loading:

Wind erodes snow from the windward (upwind) side of obstacles, such as a ridge, and deposits the same snow on the leeward (downwind) terrain. Wind loading is a common denominator in most avalanche accidents. And no wonder because wind can deposit snow 10 times more rapidly than snow falling from the sky. Moreover, wind-drifted snow is ground up by bouncing along the snow surface and when it comes to a rest it is often much denser than non-wind loaded snow. In other words, it not only adds significant weight on top of buried weak layers but it forms a slab that can propagate a fracture very easily. Wind can turn very safe snow into very dangerous snow in a matter of minutes. Wind is usually the most important weather factor in avalanche accidents.

Forecaster:Tom Mattice