Avalanche forecasting: Snow density in relation to precipitation

1. Avalanche forecasting: Snow density in relation to precipitation Lena B, Emma L, Jenna T

2. Introduction to snow density Why look at snow density? • Avalanche science • Water content

3. Our Hypothesis Research Question: Is snow density affected by change in weather? (ie. snow and rain) Claim: The density of snow will be greater after heavy rainfall due to increased water content in the snow that causes compression, therefore increasing mass and density. Conversely, after a snowfall, the density of the snow will decrease.

4. Water compacts snow → added weight causes snow to slide down in clumps • Weak layers • Rain increases separation Reasoning

5. Materials Methods • 250 cc sampling cylinder • 9 ziplock bags • Scale • Ruler • pH meter • Pick sites for data collection • Twist cylinder into upper layer of snow up to designated line • Shovel away snow from cylinder • Slide clipboard underneath cylinder • Place snow sample into bag • Measure mass of sample + bag • Subtract bag mass (~6 g) • Calculate snow density (g/cm^3)

6. Our Sites Forested Area Meadow

7. Data

9. Statistical Evidence Comparing Day 1 to Day 2

10. Statistical Evidence Comparing Day 1 to Day 3

11. Statistical Evidence Comparing Day 2 to Day 3

12. Potential Sources of Error • Measuring instrument lacks sophistication → inconsistent volume • Small sampling size • Scale doesn’t provide exact measurements

13. Findings • Our claim was supported by evidence acquired through data collection, statistical testing, and further online research • Data collection showed a higher density for snow collected after a rainfall than before • 2 sample T interval proved that the true mean value of snow density pre-rain was less than the true mean value of snow density post-rain • P value < .05 • Findings by Jim Frankenfield, director of CSAC Avalanche Center, show how our data has an effect on snow packs and avalanches • “If the precipitation comes in the form of graupel or rain it generally has an adverse effect on stability...Rain wreaks havoc when it percolates into the snowpack. Free water tends to make weak layers weaker. It can also flow along planes parallel to the ground, such as crusts, lubricating bed surfaces.”

14. Implications of our findings • Our results correspond with avalanche danger levels • Density is not perfect BUT… it remains a decent indicator • (3/20) No precipitation → 2 • (3/21) Rain → 3 • (3/22) Snow → 4 https://www.sierraavalanchecenter.org/week-in-review/current

15. Future Research Questions • How does the density of different layers of snow increase the likelihood of an avalanche? • How do weather changes (ie snow or rain) affect the density of lower layers of the snow pack? • How does temperature change have an affect on snow density? • How is density affected by tree coverage or lack thereof? • How does human presence affect the density of lower layers of snow and how might that have an effect on the occurrence of avalanches?

16. Thank you!

17. Websites • https://brooks-range.blog/2012/01/12/why-measuring-snow-density-matters/ • https://www.nrcs.usda.gov/wps/portal/nrcs/detail/or/snow/?cid=nrcs142p2_046155 • http://www.snowman-jim.org/papers/rambler.html • https://www.sierraavalanchecenter.org/week-in-review/current