City and Borough of Juneau
155 S. Seward Street
Juneau, Alaska 99801
tel. 907-586-5240
fax 907-586-5385
http://www.juneau.org

Urban Avalanche Advisory

Current Advisory as of Wednesday, March 22, 2017

Expires 7:00am on Thursday, March 23, 2017
Issued by Tom Mattice


Avalanche Danger Level 3

Click here for danger definitions



Today's Discussion

The National Weather Service Forecasts-

Today- Cloudy. Scattered rain showers in the afternoon. Highs around 40. Northeast wind 10 to 20 mph.

Tonight- Numerous snow showers and rain showers. Snow accumulation to 1 inch. Lows 28 to 34. Northeast wind 10 mph.

Thursday- Numerous snow showers in the morning, then numerous rain showers. Snow accumulation to 1 inch. Highs around 40. northeast wind 10 to 15 mph.

Temperatures climbed to above freezing yesterday in our mountain regions for the first time in a while and many places have still not returned to below the freezing point. Eaglecrest saw a daily high 34f and while Mt Roberts climbed beyond 37f. Currently Eaglecrest is showing 30f at the base... 32f at mid mountain and 27f on summit. So the mid mountain gauge almost appears off a little but it could just be a pocket of warm air.

Winds were calm for the most part yesterday and then picked back up to 20-30 after 2am. Winds currently are 15-20 out of the NE around the region. Not often do you see NE winds and rain... looks like the end of winter is near.

We have seen tremendous weakness over the last week around the region. Yesterdays warm temperatures may start to help heal this over time and yet only if we see diurnal fluctuations where temps drop back below freezing at night. Prolonged periods of above freezing temperatures bring more instability and questionability to the weak layers currently in place.

The forecast for today calls for continued warm temps with some light rains later in the day and overnight. But the forecast volumes appear to be very low.

With a weak layer throughout the region and above freezing temps for 24+ hours now... there is a possibility of wet loose avalanches and also a possibility of slab avalanches down to the persistent weak layer in place. And be extremely cautious as one could be the trigger for the other... be aware of your position in the terrain and avoid lingering in avalanche paths.

With a possibility of natural avalanches and human triggered avalanches still likely in places the forecast remains CONSIDERABLE today.

The temps are very near freezing and the rain volumes are very low. We may see little to no avalanche activity and yet its important to remember with windloading warm temps, and precip all adding to the weakness already in place avalanche danger is out there and not to be ignored.

Please continue to avoid the Flume Trail. It will probably start to shed in the near future and the weak layer in this path may be quite deep.


Primary Avalanche Problem


PERSISTENT SLAB
Persistent Slab

AVALANCHE PROBLEM
Avalanche Size Level = LargeAvalanche Probability = LikelyAvalanche Danger Trend Next 24 Hours = Stable

Description

We have several reactive weak layers in the region. This weakness is widespread.

We have seen both natural and human triggered avalanches on it in the last week and human triggered slides are still very likely.

Dig pits and look to see what the bed surfaces are where your riding? How is the bonding at 35? 50? 75cm? The depth may vary a great deal due to windloading. But these are sizeable slides and not to be ignored.

Secondary Avalanche Problem


LOOSE WET
Loose Wet

AVALANCHE PROBLEM
Avalanche Size Level = SmallAvalanche Probability = LikelyAvalanche Danger Trend Next 24 Hours = Increasing

Description

With continued near and above freezing temps look to see wet loose avalanches.

These can be easily started from snow falling off of trees and rocks in steep sections. It gathers mass and speed... then can often be the source of a trigger for the larger avalanches... these small slides are not to be ignored when you have a greater instability in the region.

If we see much direct sunlight you can expect greater levels of activity. If temps remain cool and clouds stay overhead activity will remain to a minimum.


Today's Avalanche Tip

Here is a link to a 20 minute avalanche awareness lecture from AIARE called introduction to avalanches and unstable snow.

https://www.youtube.com/watch?v=VF5Bg_qyJpg

This Advisory applies to the Mt. Juneau Avalanche Zones



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