With spring on its way, we look back at what snow crystals mean.

April 9, 2020 The 'story' of a storm, in three 'chapters' We have been saying for a while that the different shapes of snow crystals that you see under your macro lens are caused by different combinations of temperature and humidity in the atmosphere. Now we'll unpack exactly what that looks like.  From the data that you submitted last year, we analyzed the February 13-18, 2019 storm that had three unique ‘chapters’ to its ‘story’. We actually presented this analysis at last year's Western Snow Conference! Read on to learn how the weather links to the snow crystals that you sent us.  Chapter 1: Atmospheric River The Atmospheric River phase was relatively warm, and it spent about a week over the Pacific Ocean and then came from the Southwest over the Sierras from February 13-14, 2019 (below left). This part of the storm dropped 4.5 inches of snow water equivalent (SWE). That is a lot of water! Tahoe City saw dendrite and needle snow crystals, while Reno saw columns and needles. Both places saw crystals with large rime droplets on the crystals, indicating a lower level of aerosols - or impurities - in the clouds in this segment of the storm (below center and right). Chapter 2: "Cold pool" Scientists used the term "Cold Pool" to describe this 'chapter' of the storm, it meant that a cold maritime flow came from the northwest over of the Gulf of Alaska (below left). This took place from February 14-17, 2019, producing 2.8 inches of snow water equivalent. Comparted to the atmospheric river, the much colder air allowed more aerosols to infiltrate the cloud, decreasing drop size. This smaller water droplet size caused much smaller riming on crystals that came down. (Rime - do you remember that word? It refers to the tiny water droplets that freeze onto the surface of a snow crystal or other surface.) The Lake Tahoe and Reno areas both saw columns, needles and dendrites with small, opaque rime droplets (below center and right).  Chapter 3: Northeasterly flow The Northeasterly Flow moved in from the northeast on February 17-18, 2019 which cut off all of the previous moisture flowing in from the west (below left). This part of the storm was very dry, creating only 0.3 inches of snow water equivalent. Very dry storms are unique because they produce predominantly snow crystals that are formed by water vapor alone (no water droplets), and thus have little to no riming on the surface. All around the Tahoe-Reno area we saw clear and nearly pristine columns, bullet rosettes and dendrites (below center and right). Your donations hard at work this year. When you donate for a Stories in the Snow kit, the proceeds support outreach to schools in the Reno and Tahoe regions. This season, we worked with 881 students in 15 classrooms at 11 different schools. All of this thanks to YOU and our fabulous AmeriCorps Members!  Your contributions made a difference.  Thank you again from the citizen science team at DRI! Follow @StoriesInTheSnow to stay up to date about the project and see the latest snowflake images! meghan.collins@dri.edu • 775-673-7659 • www.dri.edu/storiesinthesnow

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