Avalanche Advisory Archive Pre-2016

Date Issued:2013-01-30
Danger:3
Trend:3
Probability:4
Size:2
Problem:0
Discussion:

The National Weather Service Forecasts-

TODAY...SNOW LIKELY WITH AREAS OF FREEZING DRIZZLE IN THE
MORNING...THEN SNOW AND RAIN IN THE AFTERNOON. SNOW ACCUMULATION AROUND 1 INCH. HIGHS AROUND 33. EAST WIND 10 MPH.

TONIGHT...RAIN AND SNOW LIKELY. LOWS AROUND 31. NORTHEAST WIND 5 MPH.

THURSDAY...RAIN LIKELY. HIGHS AROUND 38. SOUTHEAST WIND 5 MPH.

Temperatures continue warming today. Temperatures have come up by 30+ degrees in the last 48 hours.

We received 3+\" of snow during the cooling portion of the storm on the night of Sunday 27th. This left a layer of super cold dry snow that does not tend to bond well.

We received considerable windloading along the channel shortly thereafter with winds from 20-40. Yet a fair amount less on Douglas Island with winds only reaching the mid 20's for a period of time.

This layed down a weak layer topped with a wind slab in some areas on lee slopes. We can assume it is more of a concern in places with the more prominent winds.

During the coldest period of the event we did not receive very much snow yet as the precip began temperatures started their rising trend. This tends to lay down heavier denser snow over looser lighter snow... and in our case this is all on top of some tender shallow wind slabs spread spatially throughout the snowpack.

We have received 30mm (1.2\") of precip in the last 26 hours. This is a considerable loading rate which by itself raises a red flag of building avalanche conditions. This left about 10\" of snow at the Mt Roberts Tram Weather Station after settlement is taken into consideration. All of this during a major temperature swing creating an upside down snowpack on top of the shallow wind slab we said my be present in places.

Of interesting note is the Mt Juneau new weather station at the top of the White Avalanche Path. Sunday we layed down the 4\" of new snow... then the wind event stripped all of it away... even reducing the new snow depth more than at the beginning of the event. Then in the last 30 hours we added only 4\" of new snow. So overall during the last 5 days the Mt Juneau gauge showed no appreciable snow gain. But you can assume that snow ended up somewhere adding to the backside of the stability equasion someplace else.

This shows us the spatial variability nature of this recent new snow fall event. In some areas you may only have a few inches of new snow that is slightly upside down... in other areas you may see 1-2' of new snow with a weak layer, a windslab, and an additional upside down snowpack resting on top of that slab...

Spatial Variability is the word of the day.

With less than .25\" of precip in the forecast for the next 24 hours, only about 2 degrees of warming, and light to moderate winds avalanche danger is MODERATE to perhaps Considerable in places today.

Natural avalanches unlikely, yet possible with this weak layer, windslab, and upside down snowpack seeing some additional loading.

Human triggered avalanches are probable, especially if you find the mouse trap burried spatially in our upside down snowpack.

Please avoid the Flume and Perseverence Trails. Please do not walk above the gates in the Berhands neighborhood. Please do not park, walk, or job along thane road.

If you choose to head out into the backcountry today be aware of these conditions. Evaluate the snow conditions where you choose to recreate to see if you have the shallow weak layer or the deeper instability.

Avoid terrain traps, steep convex rolls, unsupported slopes and choose your routes wisely!

Have a great day!

Tip:

Spatial Variability-

Spatial variability occurs when a quantity that is measured at different spatial locations exhibits values that differ across the locations.

Studies of the spatial variability of snow stability and the snowpack have been one of the core themes of research at Montana State University's Earth Sciences Department since the 1960s. The National Avalanche Center is cooperating with researchers from Montana State University and the Swiss Federal Institute for Snow and Avalanche Research to continue to investigate spatial variability at a number of spatial and temporal scales.

Spatial variability at the mountain range scale

Spatial variability at the mountain range scale is extremely important for regional avalanche forecasters, who typically try to predict snow stability over large areas. In spite of this, little formal research on spatial variability at the mountain range scale has been conducted, though experience has demonstrated that the snowpack clearly varies with known parameters like elevation and aspect. In the mid-1990s we worked on a project investigating the spatial variability of snowpack and snow stability measures in the Bridger Mountains over an area of several hundred square kilometers. The research utilized six teams of observers who were shuttled around in helicopters to collect data from over 70 snow pits in a given day. The results demonstrated that statistically significant patterns of snow stability exist, and that these patterns can change through time. During sampling, more unstable conditions existed at higher elevations and more northerly aspects. This work formed the basis for Karl Birkeland's dissertation research [download the dissertation here, but realize it is a big 14 MB file!] and was presented at the International Snow Science Workshop and published in this article the Journal of Glaciology.

Spatial variability at the slope scale

The snowpack varies widely over short distances, and knowledge of these variations is critical for forecasting avalanches. Natural avalanches are believed to release from zones of localized weakness, while triggered avalanches can be released more easily from relatively weaker areas. All of this has implications for the placement of explosives for avalanche mitigation work and the positioning of snow pits to accurately assess the avalanche conditions while traveling in the backcountry. Since the late-1980s we have been interested in the spatial variability of snowpack properties at the slope scale. A project from 1988 to 1990 utilizing the digital resistograph formed the basis for Karl Birkeland's MS work, which was summarized in this article in the Journal of Glaciology. The results demonstrated that average snow strength was relatively high in areas of wind drifting and relatively low in areas with a thin snowpack or areas over the top of rock outcrops.

Spatial variability on uniform slopes

In the late 1990s Chris Landry, a MS student in Montana State University's Earth Sciences Department, worked with the National Avalanche Center to investigate variations in snow stability at the slope scale using the Quantified Loaded Column Test he developed. His research involved doing 10 QLCT tests in each of five locations on 30 by 30 m planar, wind-protected slopes with a relatively uniform substrates. His results showed that about a third of all of his snowpits could not reliably predict the snow stability of even these small plots. The reasons for these variations are not entirely clear, but are being further investigated. Complete results are reported in a paper for the 2002 International Snow Science Workshop, and in an article for Cold Regions Science and Technology. Or, you can look at his whole thesis here.

Spatial variability through time

The National Avalanche Center is currently working on a project looking at changes in slope scale spatial variability through time. We hope that this project might improve avalanche forecasting by enhancing our understanding of the conditions that lead to more or less variable snowpack conditions on slopes. This project will utilizes the SnowMicroPen and stability tests to look at the spatial variability on parts of uniform slopes through time. Some of the ideas for this project came out of our work with Chris Landry, and were presented at the 2002 International Snow Science Workshop in this paper, and some preliminary results are reported in this article for the Annals of Glaciology. This research is being funded by a National Science Foundation Grant awarded to Kathy Hansen, Karl Birkeland, John Borkowski and Ed Adams. In addition to Montana State University, cooperators on the project include the Center for Snow and Avalanche Studies, and the Swiss Federal Institute for Snow and Avalanche Research.

The project also continues to investigate slope scale spatial variability of snow stability and snow structure. Spencer Logan did his MSc on this project, investigating spatial and temporal changes in shear strength and stability using the shear frame test. He presented this work at the International Snow Science Workshop in Jackson Hole in 2004. You can check out his ISSW paper here, or his entire thesis here.

Eric Lutz has also been working on this project as part of his PhD work at Montana State University. His focus has been on analyzing and interpreting the data from the SnowMicroPen (SMP). You can check out his ISSW paper here.

Another person working on the project from January, 2004 to June, 2005 has been post-doctoral researcher and assistant research professor Kalle Kronholm. Kalle has been involved in all aspects of the project, helping to organize field work and data, assisting with advising students, programming analysis tools for the data, and working on a cellular automata model to supplement our field data collection. You can read his ISSW paper here, and he has several other papers in the works (as of summer, 2005).
References and associated Nat'l Avalanche Center papers on spatial variability:

Birkeland, K.W., K.J. Hansen, and R.L. Brown. 1995. The spatial variability of snow resistance on potential avalanche slopes. J. Glaciology 41(137), 183-190. [Abstract] [Article]

Birkeland, K.W. 1997. Spatial and temporal variations in snow stability and snowpack conditions throughout the Bridger Mountains, Montana. Ph.D. Dissertation, Department of Geography, Arizona State University, Tempe, Arizona. 205 pp. [Warning! This is a big file, so you'll want a fast connection! PDF (14 MB)]

Birkeland, K.W. 2001. Spatial patterns of snow stability throughout a small mountain range. Journal of Glaciology 47(157), 176-186. [Abstract] [Article (3.6 MB)]

Birkeland, K.W. and C.C. Landry. 2002. Changes in spatial patterns of snow stability through time. Proceedings of the 2002 International Snow Science Workshop, Penticton, BC, Canada, 482-490. [Article]

Birkeland, K., K. Kronholm, M. Schneebeli, and C. Pielemeier. 2004. Changes in the shear strength and micro-penetration hardness of a buried surface hoar layer. Annals of Glaciology 38, 223-228. [Abstract] [Article]

Birkeland, K.W. and K. Kronholm. 2004. A comparison of the spatial patterns of penetration resistance of slabs and weak layers. Proceedings of the 2004 International Snow Science Workshop, Jackson Hole, Wyoming. [Extended abstract]

Birkeland, K., K. Kronholm, and S. Logan. 2004. A comparison of the spatal structure of the penetration resistance of snow layers in two different snow climates. Proceedings of the International Symposium on Snow Monitoring and Avalanches, Manali, India, in press. [Article]

Kronholm, K. 2004. Spatial variability of snow mechanical properties with regard to avalanche formation. Ph.D. Dissertation, Department of Geography, University of Zurich. 187 pp. [PDF (6 MB)]

Kronholm, K. and K.W. Birkeland. 2004. Relating spatial variability to snow stability using a cellular automaton model initialized with field data. Proceedings of the 2004 International Snow Science Workshop, Jackson Hole, Wyoming. [Article]

Landry, C., K. Birkeland, K. Hansen, J. Borkowski, R. Brown, and R. Aspinall. 2002. Snow stability on uniform slopes: Implications for extrapolation. Proceedings of the 2002 International Snow Science Workshop, Penticton, BC, Canada, 532-539. [Article]

Landry, C.C. 2002. Spatial variations in snow stability on uniform slopes: Implications for extrapolation to surrounding terrain. M.S. Thesis, Department of Earth Sciences, Montana State Universtity. 248 pp. [PDF (900K)]

Landry, C., K. Birkeland, K. Hansen, J. Borkowski, R. Brown, and R. Aspinall. 2004. Variations in snow strength and stability on uniform slopes. Cold Reg. Sci. Tech. 39, 205-218. [Abstract] [Article]

Logan, S., K. Birkeland, K. Kronholm, and K. Hansen. 2004. Temporal changes in the spatial variability of shear strength and stability. Proceedings of the 2004 International Snow Science Workshop, Jackson Hole, Wyoming. [Article]

Logan, S. 2005. Temporal changes in the spatial patterns of weak layer shear strength and stability on uniform slopes. M.S. Thesis, Department of Earth Sciences, Montana State University. 157 pp. [PDF (5.5 MB)]

Lutz, E.R., K.W. Birkeland, K. Kronholm, K. Hansen, and R. Aspinall. 2004. Correlating snow micro-structure with snow shear strength. Proceedings of the 2004 International Snow Science Workshop, Jackson Hole, Wyoming. [Extended abstract]