Urban Avalanche Advisory

Current Advisory as of

February 19, 2020

Expires 7:00 AM the following morning.

Issued By Tom Mattice

Danger Level: 3 - Considerable
View Danger Definitions

Today's Discussion

Good morning and welcome to the Juneau Urban Avalanche Advisory. This is Tom Mattice- CBJ Emergency Programs Manager and Avalanche Forecaster.

Please remember this advisory is intended for the Urban areas of the City and Borough of Juneau and is Not a Backcountry Forecast.

If you are recreating in the backcountry please take avalanche educational courses and learn to make the educated decisions you need to make to increase your personal safety.

The National Weather Service Forecasts-

Today- Rain and snow in the morning, then scattered rain showers and snow showers in the afternoon. Snow accumulation up to 2 inches near eaglecrest. Snow level 1100 feet in the morning. Highs in the upper 30s. Southeast winds 15 to 20 mph shifting to the southwest 10 to 15 mph in the afternoon.

Tonight- Widespread rain showers and snow showers in the evening, then numerous rain showers and snow showers late. Near downtown juneau and douglas, numerous rain showers. Little or no snow accumulation. Snow level 800 feet. Lows in the mid 30s. southeast winds 10 to 15 mph.

Thursday- Rain and snow. Rain may be heavy at times in the afternoon. Snow accumulation up to 1 inch. Snow level 700 feet increasing to 1000 feet in the afternoon. Near steady temperature in the mid 30s. Southeast winds 10 to 15 mph increasing to 20 to 25 mph in the afternoon

LONG TERM...The challenges of winter-time split flow persist in the mid- range into early next week, as moist Pacific systems rail across 50 N and occasionally from latitudes southward and interact with persistent and colder Bering Sea systems that periodically replant themselves in the Gulf of Alaska. This introduces many complications that frankly models (and forecasters) often struggle with. With temperatures marginally hovering in the meteorologically scary neighborhood of the mythically well-marked rain/snow line, small error potential can span the impact scale from little to great.

Temperatures remain quite warm around the region.  Yesterday AM Eaglecrest was 33f.  It touched 35f for a while and is back to 33f again this morning.  Powder Patch is a little better at 31f while the summit is still down at 28f currently.  The Mt Roberts Tram is right at freezing this am at 32f.

These warm temps cleaned off a lot of trees and rocks from steep faces.  We saw wet loose avalanches at lower to mid elevations in the region.  I would expect to see more of this activity today and especially tomorrow as temps remain warm and precipitation rates increase.  On the bigger pitches of mountains around town these can sometimes be sizeable avalanches with all of the snow we have on the ground currently.  These warm temperatures do help the snowpack long term to settle, bond, and build strength but when temps are above freezing be aware danger lingers.   Its also important to remember that one small chunk of snow off a tree limb can start a small wet loose avalanche and on the wrong slope it can turn into the trigger for something much greater.

We did not see much precipitation around the region in the last 24 hours.  Just a trace at Eaglecrest with .5mm SWE and only 2mm at the Mt Roberts Tram.  With the combination of warm temps and a little rain we lost snow at our Mid Mountain elevations.  Both Douglas and the mainland lost several inches of snow.

Temperatures remained below freezing all day as they have in the past few weeks at upper mountain elevations.  So the snowpack is a little less settled, a little more questionability remains, and we have seen a great deal of wind.  Yesterday winds were constant in the 20's for much of the time and last night Douglas saw 50mph winds while the channel saw slightly less winds but still well into the 30's for periods of time.  Currently winds at blowing out of the ESE with the Tram showing 25-30mph and Eaglecrest showing 30-45mph.  Todays forecast calls for continued winds and over.5" of SWE.  This should remain in the form of snow at upper elevations.  Expect to see weak windslabs in places around the region today on N-W facing slopes.  These will continue to build and weaken throughout today and into tomorrow as temps again warm and precipitation rates increase.

Yesterdays snowpits tests showed a fairly strong snowpack.  The deep persistent slab remains down at 185cm where I looked yesterday but is quite resistant to tests.  The primary concern I saw was the storm slab from the last 9 days.  Its down at 90cm but also remains quite strong to tests.  But we have seen failure in the region on this weak layer many times in the last 9 days so it remains one to watch.

With continued warm temps and over .5" of SWE today I expect to see continued wet loose avalanches occurring.  With high winds I expect to see windloaded areas become sensitive to triggers even though they will probably not fail naturally.

Avalanche danger remains CONSIDERABLE today.  Natural avalanches remain possible and human triggered avalanches are more likely in windloaded areas.

Please continue to avoid the areas above the gates in the Behrends Neighborhood.   Mt Juneau has tremendous snow volumes on the upper faces.   Tomorrow dangers in this areas will continue to increase as the precipitation rates and temps increase.

Please also continue to avoid the Flume trail.  We did see some snow come out of Chop Gulley last week but this path is also quite loaded and has potential for greater events.

Primary Avalanche Problem

Loose Wet

Problem Type:Loose Wet
Avalanche Size:Small
Avalanche Likelihood = Likely
Avalanche Trend = Increasing Danger

Description

With above freezing temps to mid mountain and above today and .5" of precipitation in the forecast expect to see Wet Loose avalanches today.

These can start quite small and yet on some of our terrain become quite large.  These can also be the trigger for the deeper weak layers in place.

A true worst cast scenario is a small wet loose slide triggers the storm slab that is 90cm down which gets rolling and then triggers the Deep Persistent Slab at 185cm down.  Although the odds of this occurring are not high we have enough snow now that it would not be a good thing!  For this reason we need to continue to limit our exposure to more advanced terrain during these heightened periods of instability.

Tomorrow both temps and precipitation rates increase.  Showing an increasing danger trend.

Learn more about Loose Wet.

Secondary Avalanche Problem

Wind Slab

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

Description

We had a lot of soft loose snow two days ago at all elevations.  Night before last we saw 20+mph winds for most of the night.  Last night winds increased around the region to 30-50+mph.

Winds have been primarily out of the ESE leading to windloading on our N-W facing slopes.

Be aware that windloaded areas will be potentially trigger sensitive today yet we may not see enough new snow or wind to create natural triggers.

With new snow coming in today during more winds dangers will continue to trend up slightly.

Learn more about Wind Slab.

Today’s Avalanche Tip

Avalanche Canada has created a great tool to practice your routefinding.  Its a fun game to teach others how to manage terrain more safely.

https://www.avalanche.ca/tutorial/reducing-risk-in-the-field/route-finding-exercises