Unstable Conditions: Planning a Day

Posted on 1/13/2014

In today's post I want to take the take to cover how to plan a ski day when the conditions are likely to be unstable. You might find this through the avalanche forecast, prior conditions, or the weather forecast.

As an example, this past weekend on 1/13/2014, I went skiing in an area called Mores Creek Summit in Idaho. You can find the Google Maps, CalTopo Maps, and current conditions here by using the SnowGeek trip planning tool.

The nearest avalanche forecast center with similar conditions is the Payette Avalanche Center. The forecast for the day previous is here. Reading the forecast, it mentions that the danger should rise from moderate to considerable with the next storm, which was forecasted to arrive the night and day of 1/12 and 1/13. This means that natural avalanches are possible and human triggered are likely in avalanche terrain.

Under conditions like these, the best thing to do is to avoid steep slopes and enjoy skiing and snowboarding on low angle slopes. Usually this would mean traveling under 35º slopes, but because of an instability due to surface hoar the angle needs to be reduced even more. Unlike other instabilities, surface hoar weak layers tend to break at unexpected low angles. Generally a good rule of thumb for these instabilities is to limit skiing on slopes 30º or less.

One tool to plan a trip to avoid slopes steeper than 30º is CalTopo. When you use the SnowGeek trip planning tool, it pulls the CalTopo map as well. It is a tool that shades a combination of Google Maps and Topographic maps with colors to represent slope angle. Below is an example map from the area. You may have to pull it down and to the right to see the backcountry area above the road marked in red.

CalTopo gives a great general picture of terrain, but its also important to have a good sight through inclinometer to measure a slopes' angle before descending. Topo maps often miss small, micro terrain features and its always important to know the exact angle of the slope you are dropping on. The tool for unstable days like this is unequivocally a sight through inclinometer. Many compasses and phones now come with these, but a dedicated inclinometer such as this one is the best option.

From the map on CalTopo (visit link), it is easier to determine where are steep starting zones and also take notice of low areas which end in gullies.

By now, we have now looked at the avalanche forecast and the topo map with steepness shading. The next piece of data is the weather forecast, which is also provided when you make a query using the trip planning tool. The avalanche forecast mentioned that conditions would become considerable as the storm started. This would be easily seen by the NOAA weather forecast that is provided as part of the data returned.

The last piece of information would be to take a look at Snotel data. The Snotel system is maintained by the National Resources Conservation Service (NRCS). It provides current and historical conditions about temperature and snowfall among other things and can be reached via the "Snotel" tab in the SnowGeek trip planning tool. Below is a screenshot of the past 72 hours from Noon 1/14/2014.

In the plot, you can see that storm is leaving snow at about 36 hours back, which is the night between 1/12 and 1/13. The morning of the ski day you would be able to tell that the storm was beginning to drop snow. The other interesting trend is before that when the temperature rises above 0ºC and precipitation comes as rain.

By combining the avalanche forecast with both NOAA weather forecast information and current conditions from the Snotel system, it was possible to see the day of before driving to ski that conditions would be avalanche prone and to plan appropriately. Fortunately, based on the topo map and prior experience it was possible to plan a tour with great skiing while staying in low angle terrain.

Its always important to take observations during the ski day, but almost as important is to be aware of the conditions before arriving. In this case, our guess matched reality and we got some great photos of the unstable conditions along with a video of some great skiing.

The first two photos are of a whumpf and shooting crack, the third is an older crown from the day before.

Pedro Rodriguez

Snow Geek