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Juneau Urban Avalanche Advisory

Issued 0646 Friday February 16, 2007 by Bill Glude.

Valid through 0630 Saturday February 17, 2007 unless updated.

SORRY, THE COMMUNITY DID NOT COME UP WITH FUNDING TO CONTINUE THIS PROGRAM. WE STAND READY TO REVIVE IT IF AND WHEN FUNDING IS AVAILABLE.

THIS SAMPLE PAGE IS PROVIDED AS AN EXAMPLE ONLY. IT IS NOT CURRENT.

Today's Discussion

Yesterday's moderately heavy rain and snow has tapered off and is forecast by the Weather Service to be showers with a snow level of 250 m (800'). With a slower loading rate, the avalanche danger has decreased. If the forecast east winds start transporting snow later today, we may update this forecast.
The one threat for larger slides is a glide crack system in the starting zone of the White path. Glide cracks can unpredictably release full depth avalanches. We will be monitoring the area closely.

Today's Avalanche Tip

The loading rate is a critical factor in avalanche release. If the snowpack has some weakly-bonded layers to begin with, rapid loading with new-fallen or wind-transported snow is likely to release slab avalanches. Avalanche specialists call loading by wind-transported snow wind loading, it is very important because it can load the snowpack at up to ten times the rate of snowfall without wind.

On the other hand, a slow loading rate like that in today's forecast allows the snowpack time to adjust to yesterday's load, gaining strength through settling and bonding.

Using This Advisory

The usual levels of concern for avalanches large enough to reach developed areas are Serious and higher on the urban avalanche danger scale.

When avalanche danger is at High or Extreme, it is wise to limit your exposure time or stay out of the avalanche zones.

In a typical year, avalanche danger is not High or Extreme much of the time. There may be perhaps two weeks' total time when the avalanche danger is at those levels. But slides may or may not actually release when the danger level is up.

Avalanche danger is like forest fire danger; if the fire danger is High and no one drops a lit cigarette, no one leaves a campfire burning, and there are no lightning strikes, there will be no wildfire because nothing has initiated it. But the danger level is still High.

Lack of release does not mean the potential was not there. We will commonly forecast the potential ten or more times for every time slides occur. This is just the way avalanches are. There are many subtle factors involved in their release. They may not release because there was no trigger, or not quite enough loading from wind transported snow, or the forecast thaw was not quite pronounced enough.

This forecast is for the urban paths on the Gastineau Channel side of Mt. Juneau only, not for Thane Road or for the Juneau area backcountry. Beware, Mt. Juneau conditions are often markedly different from those in other areas nearby. Do not attempt to apply this forecast to other areas.
If you are wondering where the mapped urban avalanche zones are, check the Juneau Urban Avalanche Maps page.
We always welcome observations of avalanche activity or of what you have found in the field, and need them to help us produce the most-accurate forecasts. E-mail to the address on the Contact Us page, or call us as 586-5699.
Archives and information on the backcountry advisory program from 2004-05 and 2005-06 are here. Our backcountry advisories are temporarily suspended due to lack of funding, but we stand ready to reactivate and expand them as soon as funding materializes. We keep them on the site as references and as examples of what we could do with a little more funding.

This service is made possible by City and Borough of Juneau funding and in-kind support.