Urban Avalanche Advisory

Current Advisory as of

January 21, 2019

Expires 7:00 AM the following morning.

Issued By Tom Mattice

Danger Level: 2 - Moderate
View Danger Definitions

Today's Discussion

The National Weather Service Forecasts-

Today- Widespread rain showers and snow showers. Snow accumulation to 1 inch. Highs around 35. Southeast wind 10 mph.

Tonight- Rain with snow likely. Snow accumulation to 3 inches. lows around 31. Southeast wind 10 mph.

Tuesday- Cloudy. Chance of rain and snow. Highs around 37. South wind 10 mph.

This snow event has slowly come on over the last 36 hours.  When the snow started Eaglecrest was around 20f degrees and has since risen up to 29f.  Mt Roberts is much the same having started snowing at 21f and now the temp is right at freezing at 32f.

During the last 36 hours Eaglecrest is showing about 15cm of new snow from 16mm of precipitation.   Mt Roberts is showing more snow with 20cm on the gauge for the last 36 hours from 18mm of precipitation.

Winds are moderate to considerable.  They started the storm out quite low but have continued to build.  Current winds are 18-22mph out of the SE.  This will add to todays danger equation.

Yesterday showed a mostly stable snowpack.  The new snow was not bonding all that well to the old snow surface.  Look to see shallow windslabs building on NW Slopes.

There are a few deeper weak layers in place still.  The rain and warming did not heal the deeper weak layers as much as we had hoped.  As loading continues we have several weak layers deeper in the pack we will want to keep an eye on.  Loading on those layers will be critical.  It looks as though todays weather into tomorrow does not call for that great of precipitation and snowfall rates.  These lower loading rates should help keep the danger more to the surface layers for the time being.

You will want to perform snowpit tests over the next week or so and see how this load starts to effect the deeper weak layers in place.

Use extra caution today especially in windloaded areas.  In general urban avalanche danger remains LOW due to low snow volumes but overall avalanche danger is MODERATE.  Natural avalanches are unlikely due to low loading rates and yet human triggered avalanches are possible especially in windloaded pockets.

Primary Avalanche Problem

Wind Slab

Problem Type:Wind Slab
Avalanche Size:Small
Avalanche Likelihood = Likely
Avalanche Trend = Steady Danger

Description

We have seen 12-20cm of new snow around the region in the last 36 hours with winds from 10-20 gusting to 25mph out of SE (130).

This snow came to rest on a hard icy bed surface.  Bonding may be in question a while longer.

Look to see shallow windslabs building on NW slopes.  These may be fairly easy to trigger.  Probably not huge in nature yet on steep slopes may travel faster than average with low density snow on a hard bed surface.

Learn more about Wind Slab.

Secondary Avalanche Problem

Persistent Slab

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

Description

The rain and warming were not enough to heal some of the deeper weak layers we have present in the snowpack.

Yesterdays snowpit tests still yielded low test scores on these deeper weak layers.

Its hard to always trust snowpit results as we cut the back taking away the snowpack strength  to perform our tests as we isolate the weak layers.  But the test did snow very clear planar shears  at low scores.

I think it will take a bit more loading to where these deeper weak layers come into question.  Loading rates have been low to moderate and are forecast to stay that way.

The snowpack may continue to settle and adjust to this loading rate but keep an eye on these deeper weak layers.  A slide on them is sure to be more of a hard slab with much greater consequences.

The temperature regime in the snowpack was consistent showing no great temperature gradient.  Hopefully these weak layers will continue to heal and build strength.

Learn more about Persistent Slab.

Today’s Avalanche Tip

Backcountry Basics: Recognizing Avalanche Terrain

By Dale Atkins

“We didn’t think we were in an avalanche path.”

These were the sorrow-filled words told to me by a couple whose friend was buried and killed in very small Colorado avalanche back in 2000. The problem of not recognizing avalanche terrain is not new. Avalanche survivors have likely uttered similar words for centuries, and even today the message is still heard after some accidents.

Avalanche terrain can be a broad and complicated topic. But here, I’ll introduce some ideas and key points about avalanche terrain that you may not have heard before. I hope this will encourage you to seek out information. Recognizing avalanche terrain is key to staying alive and having fun in the backcountry. You can’t control the weather or the snow conditions but you can control when you go—and where.

To read the full article go to:  https://www.msrgear.com/blog/backcountry-basics-recognizing-assessing-avalanche-terrain/

Be safe out there and have a great day.