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 Tuesday, January 17, 2017

Expires 7:00am on Thursday, January 19, 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 and snow showers in the morning...then chance of rain and snow in the afternoon. Temperatures steady 35 to 37. Variable winds to 10 mph.

Tonight- Cloudy. Chance of rain and snow. Lows 28 to 32 in the evening. North wind 10 mph.

Wednesday- Snow and rain in the morning then rain. Snow accumulation to 1 inch. Highs around 36. Northeast wind 10 mph shifting to the southeast in the afternoon.

The snowpack has seen a great deal of rain and warming recently. We have seen over 6.6" of precipitation at the Mt Roberts Tram Summit in the last 6 days. This started in snow leaving us only 20cm total accumulation after all the rains. Sadly this could have been 150+cm had it been colder. But you can assume at higher elevations and in the ice field they received much more snow.

Temperatures have been mostly above freezing for around 72 hours. Especially lower on the mountains. At uppermost elevations the snowpack remains a little cooler.

Eaglecrest received 29mm of precipitation in the last 24 hours. Mt Roberts received a little more at 34mm. All this translated into about 2cm of new snow on the Eaglecrest gauges. We can assume there is a fair amount more near summit. Mt Roberts lost snow overall but once again there could be quite a bit near summit as temperatures ranged from a high of 34 to a low of 31 at the tram and Eaglecrest was about 33f-30f at Mid Mountain.

The precipitation dried out last night about 10pm. This will start to help solidify the snowpack as temperatures are forecast to cool over the next 24 hours by several degrees back to below freezing. Time is your friend as the snowpack drains and builds new bonds again through the cooling process.

Today with the large volumes of precipitation once again avalanche danger remains CONSIDERABLE.

Danger levels will be decreasing a great deal over time. With no significant precipitation in the forecast for the next 24 hours natural avalanches are not very likely. Yet with high winds, new snow, and a great deal of precipitation/loading human triggered avalanches remain possible in places.

On the lower mountain be aware of a rotten snowpack cleaning itself off trees, steep rocky faces, etc. This activity will slow as temps fall and precip has stopped.


Primary Avalanche Problem


WIND SLAB
Wind Slab

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

Description

Keep an eye out for windslabs of new snow at uppermost elevations.

This should have bonded fairly well to the wet snow surface yet be aware that with high winds and high precipitation volumes windslabs will be questionable in places.

With cooler temps in place this layer will bond and heal quickly over time. Time is your friend.

Secondary Avalanche Problem


WET SLAB
Wet Slab

AVALANCHE PROBLEM
Avalanche Size Level = LargeAvalanche Probability = UnlikelyAvalanche Danger Trend Next 24 Hours = Decreasing

Description

With 6.6" precipitation over the last 6 days be aware of rotten snow at mid to lower elevations. This snow will not bond well to other things until it cools back off to below the point of freezing.

Be aware that you still have a giant slurpee... that has most of the liquid drained out of it... but not much keeping it in the glass right now... it will turn back to a bag of ice in the next day but it needs time to heal.

Be aware of steep open rock or grassy faces and places that have fewer anchors or steep convex rolls adding stress to the slab through creep and glide...

This danger will subside greatly over the next 24 hours with additional cooling.


Today's Avalanche Tip

This Advisory applies to the Mt. Juneau Avalanche Zones



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