Mountain Rain or Snow

If you are reading this, you may be one of the many people who contributed to submitting 1040 observations this season of rain, snow, and mixed precipitation. This graph shows a timeline of the number of observations as they were submitted in the winter and spring. The different colored points depict your answers to “What is falling from the sky right now?”  A keen eye will notice that there are a few less than 1040 observations portrayed here; that is because some observations were submitted without a geo-tag (location services were off) and other similar issues. 

The Tahoe Rain or Snow community is made up of over 200 observers who receive text message alerts during storm events. This graph shows the growth of our community through the season. Wondering why the growth curve  grew in a step-wise manner? Several organizations helped us spread the word (e.g., NWS-Reno and CoCoRaHS) and we had a lot of new sign-ups as a result.

To sign up, text WINTER to 855-909-0798.

Answers to the call for weather data came mainly from across the Tahoe, Sierra, and Truckee Meadows regions. We also had observations from the San Francisco Bay Area, the High Sierra, Fallon, Nevada, and even Portland, Oregon. Notice how the points cluster where people live. Next season, we hope to capture more observations from backcountry mountain areas where people are recreating or doing remote work.

As you look at these figures of the number of observations submitted (horizontal axis) at different elevations (vertical axis), notice how they were most often submitted from below 5200 feet (e.g., Reno/Washoe Valley) or above 5900 feet (e.g., Tahoe Basin).  Look at the next plot to see how the proportion of precipitation types of changed with elevation.

Here, we divide elevation into ‘bins’ (an extra sciency way of saying elevation ranges), so you can see the number of observations submitted at each level. It won’t surprise you to see that there are more observations of rain and mixed precipitation at lower elevations and fewer at higher elevations. Likewise, there are more observations of snow at higher elevations.

For fun, we took a look at the timing of your observations by hour (on 0-24 hour military time) and by day of the week. It seems like a lot of people like to observe over their morning coffee and during the day, but rarely at night.  Sunday was a popular day to submit, and it also looks like you all like to take the day off on Friday!

Tahoe Rain or Snow is a community of weather observers who use the Citizen Science Tahoe app to share data with scientists. During a winter storm, observers let us know “What is falling from the sky right now?” (rain, snow, or mixed precipitation) along with a geo-tag of their location.

We use this information to better understand how much water falls from the sky during the winter in the Sierra Nevada. Counter to common logic, precipitation often falls as snow at air temperatures 1°C–3°C (33.8°F–37.4°F), particularly at higher elevations and on the drier, eastern side of the Sierra Nevada. However, we have very few recorded visual observations of precipitation phase despite millions of visits to the Sierras every year.

Why does this matter? Rain and snow have different effects on the land surface. Of greatest concern to downstream water users in Nevada and California are the differences in water storage and flooding. Snowpacks act as ideal natural reservoirs—storing water throughout the winter and early spring, then releasing it as temperatures warm, and both human and natural demand increase. Rainfall does not produce this same accumulation-melt effect, instead running off during precipitation. Importantly, large rainfall events from atmospheric rivers produce such rapid runoff that flooding, landslides, and infrastructure damage can result. These storms often come in near the freezing point, making it essential we can accurately predict rain versus snow.

We are using the crowdsourced data to improve satellite and computer model predictions of rain and snow in the Sierra Nevada.