Urban Avalanche Advisory

Current Advisory as of

February 23, 2019

Expires 7:00 AM the following morning.

Issued By Tom Mattice

Danger Level: 3 - Considerable
View Danger Definitions

Today's Discussion

The National Weather Service Forecasts-

Today- Sunny. Highs around 29. Northeast wind 10 to 15 mph. Near downtown juneau and douglas, northeast wind to 35 mph with gusts to around 70 mph decreasing to 25 mph with gusts to around 45 mph in the afternoon.

Tonight- Mostly clear. Lows 12 to 18. North wind 10 to 15 mph. Near downtown juneau and douglas, northeast wind 15 to 25 mph with gusts to around 45 mph.

Sunday- Sunny. Highs around 33. Northeast wind 10 to 15 mph.

AVALANCHE DANGER IS CONSIDERABLE TODAY.  Natural avalanches were occurring around the region yesterday and human triggered slides remain likely in isolated locations with windloading as well as in other areas with persistent weak layers underlying the snowpack. Danger is not widespread and yet the slide sizes are notable.

We received nearly 2' of snow in the last 6 days.  This snow came in primarily with ESE winds during its duration.  We have seen weakness and windloading on faces from W to N with both natural and human triggered avalanches occurring on these aspects.

Winds shifted yesterday to the North.  Early on this was moving tremendous amount of snow.  Over time this loose snow near summit and ridgeline gets stripped away and some of it redeposited lower on the slopes.  Some simply sublimates into the atmosphere. Windloading although a huge factor leading to avalanche formation is less of a factor over time.  The loading rates diminish due to removal of snow available for transport.  This has allowed us to reduce todays danger from HIGH to CONSIDERABLE.  We have removed a great deal of the likelihood of natural avalanches...  Though in current conditions natural avalanches remain possible and human triggered avalanches are likely in places.

Many of the noted avalanches around the region this week were not occurring in traditional locations.  Many of them were actually lower down on the slopes showing this increased hazard in these wind deposited areas.

The urban paths although a concern still don't have quite enough load to hit structures...  but the areas above the neighborhoods on the walking trails remains in question and should be avoided another day.

Todays forecast calls for cool temperatures and high winds.  We may see enough solar warming for small wet loose avalanches and point release events...  but in general the winds should minimize warming and this likelihood.  But be aware slopes facing the sun will be a little more suspect during the heat of the day and these are also our south facing slopes taking the current windload.

Winds are currently 20-30 at the tram and Eaglecrest yet you can assume those winds are much higher along the ridgeline along the channel.  Increasing the urban loading.

Yesterday morning the tram was 20 degrees this morning it has dropped to 17.  These cooler temps should hold today.  We may see a little more diurnal warming tomorrow.

Avalanche danger is lingering around the region.  Yesterday I spotted a slide that was several hundred yards wide and nearly a 1000 vertical feet.  These are notable events.  Please limit your danger by limiting your exposure to avalanche terrain.

 

 

 

 

Primary Avalanche Problem

Wind Slab

Problem Type:Wind Slab
Avalanche Size:Large
Avalanche Likelihood = Likely
Avalanche Trend = Decreasing Danger

Description

During both storms this week that deposited 60+cm of snow we had strong winds from the ESE. This has created great potential on West to North facing slopes.

We have seen a lot of recent skier triggered avalanche activity on these layers as well as snowmobile triggered event and this was before the second, stronger half of the storm that had increased loading rates and higher winds.

Yesterday we had natural avalanche releases in many location around the region on several different aspects.

Yesterday and Today we have a Taku wind event kicking up that will greatly increase concern for the Berhands Path and others on Mt Juneau. With multiple wind events from Multiple angles stay safe out there and choose low angle slopes with limited exposure.

Learn more about Wind Slab.

Secondary Avalanche Problem

Persistent Slab

Problem Type:Persistent Slab
Avalanche Size:Large
Avalanche Likelihood = Possible
Avalanche Trend = Steady Danger

Description

We have not seen any significant activity off of Mt Juneau. There is a potential to have this deeper persistent weak layer present in this location.

During Feb 1-5 we had a cold snap at the end of a wet storm that plunged to -1f. This developed a Near Surface Faceted Layer that is now a persistent weak layer. My guess is this layer is down between 80-90cm in most locations. Deeper in windloaded areas. Perhaps shallower in wind stripped locations.

With todays Taku wind event directly loading the urban faces and this potential weak layer in place this is the reason the forecast is set to Considerable today.  Natural avalanches are quite possible and human triggered slides are likely in places.

My guess is mostly we will see size 2 events around the region but on this slope the deeper event would definitely be a size 3 plus event should it occur.  Two size 3 slides were noted yesterday in the region.

Please avoid walking above the gates in the Berhands Neighborhood.

Probably also a good day to avoid the Flume Trail.

Learn more about Persistent Slab.

Today’s Avalanche Tip

To learn more about windloading go to this handy link from Avalanche.org

https://avalanche.org/avalanche-encyclopedia/wind-loading/