About the Rate of Accumulation Chart

The rate of accumulation of snow is one important factor in assessing snow stability. If I remember correctly, snow accumulating at a certain rate for a certain period of time was part of the criteria has been used by some to help decide when avalanche control was needed.

 

This information for three different elevations, is shown in the rate of accumulation chart (below the snowpack bar graph). To generate the chart, Excel takes the amount of new snow per two data intervals from the snowpack model, and divides it by the length of time in hours of those 2 data intervals. Normally this is 2 hours,  but there are many instances of skips or breaks in the data. Excel accounts for this.

 

Example: if 2 inches of snow fell between 8 AM and 10 AM, the rate for 10 AM is displayed as 1 inch per hour. However, perhaps an hourly data transmission is missing. If the model indicates that 6 inches of snow fell between 3 PM and 6 PM, the 6 PM rate will be displayed as 2 inches per hour.

 

LR

About the Combined Chart

A third graph has been added that I hope is self-explanatory. It shows the total amount of new snow in each 2 hour data period for 3 different elevations, as well as the temperature. Six hourly maximum wind speed and noon solar radiation data have also been added.

 

This chart should give an idea of how much it snowed during the previous week and when, what the temperature was at the time as well as later and how windy it was.  With this information it may be possible make a number of inferences. Some examples:

 

- High max wind speeds during periods of snow suggests wind transport.

- Following a period of snow, temps that drop rapidly into the teens suggest clearing skies.

- A warm spell after the last snowfall, followed by cold weather may mean a frozen surface that will support a skier at lower elevations, but a not so fun and all too common breakable crust higher up. (Welcome to the Northwest backcountry. :-)

 

The noon solar radiation (with moderate temperatures) may hint at the development of a sun crust. It can serve as a check on the precip values too. After a large snowfall, noon solar radiation occurring at the same time as more new snow on the graph suggests what probably really happened; snow accumulated above the sensor, was warmed by the sun, and fell in! At least that’s what I think happened on Dec 17, 04. 

About the Cumulative Chart

The cumulative chart is an attempt to predict the spring snowpack at 3 elevations: the parking lot, the SNOTEL site, and Jolly Mt. summit. It does not account for melting (or wind transport) so the depiction snow depth at the SNOTEL site will be different than what it actually reports. The idea however, it to get an idea of the relative distribution of snow: is there not much lower down, but a lot higher up compared to seasonal averages, or not?

 

The model that creates the chart takes the amount of precip that falls as snow during each hour interval, and estimates the density that this little bit of snow will have in the spring. To make things easy, the density currently used is about 50 percent. The lapse rate at the time is used to predict whether the precip fell as rain or snow.

 

All the little bits of snow at each elevation are then added to the bar graph, with the latest snowfalls on top. The chart is read the same way as the one week bar graph, but it covers the entire snow season to date.