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

Introduction to snow density Why look at snow density? Avalanche science Water content Emma Less detail Define porosity = how porous something is,, how easily liquids can pass through Avalanche science == the more dense snow is, the more likely it is to form a slab of snow → plus the added weight of precipitation such as rain causes these slabs further instability ⇒ they fall down potentially resulting in an avalanche We are not focusing as much on water content as we are with avalanche science. However, snow density is helpful in determing water content in a designated area. This water content may help hydrologists/other curious people to understand how much water will be available in runoff → important to california’s water supply

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. Lena

Reasoning Water compacts snow → added weight causes snow to slide down in clumps Weak layers Rain increases separation Lena While water compacts snow (you might think it would help make the snow less mobile) the sudden added weight cause the snow to slide down in massive clumps Weak layers If it snows -- you add to the week layer and then the rain just causes it to slip Could or could not… Why? Runoff

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) Emma Bottle prevents packing Give barely enough info so a scientist could replicate

Our Sites Forested Area Meadow Lena

Density (x100)/snow water percent Sample Mass (g) Volume (cm^3) Density (g/cm^3) Density (x100)/snow water percent M1 28 246.793 0.113 11.346 M1.2 24 0.097 9.725 M1.3 23 0.093 9.320 F1.1 29 0.118 11.751 F1.2 22 0.089 8.914 F1.3 51 0.207 20.665 M2.1 42 0.170 17.018 M2.2 59 0.239 23.907 M2.3 82 0.332 33.226 F2.1 55 0.223 22.286 F2.2 60 0.243 24.312 F2.3 58 0.235 23.502 M3.1 61 0.247 24.717 M3.2 50 0.203 20.260 M3.3 54 0.219 21.881 F3.1 53 0.215 21.476 F3.2 F3.3 Data Emma On the left, mass goes up by 25, on the right water percentage goes up by 10 Delete graph → make table bigger Box different days and explain weather -- label it

Emma

Statistical Evidence Comparing Day 1 to Day 2 Jenna Show bar graph of difference (of means?) Write caption below to show what the graph means n=

Statistical Evidence Comparing Day 1 to Day 3 Jenna

Statistical Evidence Comparing Day 2 to Day 3 Jenna

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

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.” Jenna

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 Emma DAY THREE == Avalanche → Rapid change in density Calcuating snow desnity was a really cool experience but it also really cool seeing how it tied into actual avalanche science Advisory on sierraavalanche → week in rview Our results ultimately did fall in line with

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? Lena Just share ideas,, not always how

Thank you!

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 EMMAMAKMKAMK