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 Saturday, February 25, 2017

Expires 7:00am on Tuesday, February 28, 2017
Issued by Tom Mattice


Avalanche Danger Level 2

Click here for danger definitions



Today's Discussion

The National Weather Service Forecasts-

Today- Cloudy then becoming mostly sunny in the afternoon. Snow and rain early in the morning. Additional snow accumulation to 1 inch. Highs around 39. East wind 10 to 20 mph. Near downtown juneau and douglas, gust increasing to 35 mph in the morning.

Tonight- Partly cloudy. Lows 21 to 27. Northeast wind 10 to 20 mph diminishing in the evening.

Sunday- Mostly cloudy. Highs around 35. East wind 10 mph.

Nice to see a little new snow around the region again this morning... We received about 9cm of new snow at Eaglecrest and only 6cm or so at the Mt Roberts Tram. Winds have been calm thus far and temps remain cool. Eaglecrest is 29 at the base. 25f mid mountain and on summit. Mt Roberts is slightly warmer at 27f. Winds are fairly calm with eaglecrest showing winds below 8 and Roberts below 5.

This new snow today came to rest on a trace of new snow from two days ago over the top of a hard bed surface. This trace of new snow may have faceted a bit in places and this new snow will likely not bond well to the old snow surface.

This mornings forecast calls for increased winds. Sheep Mountain is already showing 30mph winds. This will start to develop shallow new windslabs on lee slopes. As winds increase throughout the day hazard will be building.

Avalanche danger is currently low but will rise rapidly with windloading to MODERATE today.

With the afternoon sun today we will also want to be looking for wet snow avalanches. The temperature is forecast to rise up to the point of freezing in the hills and the sun will take effect on south and west facing slopes later in the day.

With wet loose avalanches possible in the afternoon naturally and with human triggered avalanches possible after the wind slabs build in isolated locations... Avalanche danger will remain moderate into tomorrow.

The forecast calls for cooling and not much more in the way of snow. Depending on the winds avalanche danger will probably drop back to low tomorrow.

Have a great day and enjoy the snow. Just remember bonding may not be that good yet and you may see shallow isolated pockets of instability today. The depth of the slab will increase during the wind event should it transpire.


Primary Avalanche Problem


WIND SLAB
Wind Slab

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

Description

With the temperatures rising to freezing throughout the day and sun in the forecast look to see shallow wet snow avalanches on sunny slopes later in the day. Watch the South to Southwest facing slopes for activity should we see much direct sunlight and solar radiation.

Secondary Avalanche Problem


LOOSE WET
Loose Wet

AVALANCHE PROBLEM
Avalanche Size Level = SmallAvalanche Probability = PossibleAvalanche Danger Trend Next 24 Hours = Stable

Description

With the temperatures rising to freezing throughout the day and sun in the forecast look to see shallow wet snow avalanches on sunny slopes later in the day. Watch the South to Southwest facing slopes for activity should we see much direct sunlight and solar radiation.


Today's Avalanche Tip

Avalanche Problem Essentials – Wind Slabs 

Below is a link to a great article.

This document is part of “Decision Making in Avalanche Terrain:a fieldbook for winter backcountry users” by Pascal Haegeli,  Roger Atkins and Karl Klassen and provides indepth background  information  for  on  the  topic  of  Avalanche  Problem  Essentials.  

For additional background information on the topics covered in the field book visit  www.avalanche.ca/cac/decisionmaking

https://avalanche.state.co.us/wpcontent/uploads/2015/10/avchar-windslab.pdf

This Advisory applies to the Mt. Juneau Avalanche Zones



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