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New Snowpack and Precipitation Normals Now Available

Posted by Lexi Landers, Hydrologist, National Water and Climate Center in Conservation
Dec 17, 2021
1991-2020 Median Snowpack Statistics for Daily SNOTEL Data chart

Recently, the Snow Survey and Water Supply Forecasting (SSWSF) Program published new 30-year hydroclimatic normal values or “normals” for snowpack and precipitation at western U.S. monitoring stations. This information serves as a benchmark for assessing water supply conditions and is used by producers, natural resource managers and the research community.

Each decade the SSWSF Program calculates the median and average over a 30-year period to provide this data. This update shifts the reference period from the 1981-2010 period to the 1991-2020 period and includes new values for nearly 700 automated SNOTEL (snow telemetry) stations and over 900 snow course measurements at sites managed by NRCS. Data from SNOTEL stations help inform decisions for water managers, reservoir operators, producers, recreationists, and other groups.

Also included in the update are 1991-2020 medians and averages for external agency reservoir storage and streamflow volumes, used for water supply forecasting across the west.

To view the new data and to learn more about this update, visit the National Water and Climate Center Normals Website. You may also view the NWCC Interactive Map.

Category/Topic: Conservation

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Comments

Grant Parker
Dec 15, 2021

Thanks for compiling and the information is helpful. Do you have a compilation of old "normals" - basically showing how the reported normals have changed over the past century or so?

Ben Weaver
Dec 17, 2021

@Grant Parker - thank you for your comment. Unfortunately, we do not currently have such a comparison available since the normals calculation process has differed through time. This is an analysis we hope to accomplish in the future. However, the SNOTEL network only dates back to the early 1970s and many stations were not installed until the 1980s, so a comparison on normals through time will only be possible for about the past 50 years. The snow course network has a much older heritage, dating back to the 1930s or earlier, but many snow courses have been discontinued as the SSWSF program has expanded the SNOTEL network. You can view roughly how normals have changed between the 1981-2010 and new 1991-2020 reference periods by clicking on the 1991-2020 vs 1981-2010 Normals link in the basin or station pop-ups on our Interactive Map.

James Hurja
Dec 15, 2021

Thank you the report and the new normals. Very well done. I was curious how these numbers compare to past numbers but your explanation of past normals being calculated differently tells me I can not put a lot of stock into them. I figure these normals cover the complete SnoTel network. How would I find the 1991-2020 normals broken out by state, i.e., 1991-2020 normals for Utah, Nevada.

Ben Weaver
Dec 17, 2021

@James Hurja - thank you for your comment. Under the “Retrieving Normals” section on the NWCC Normals Webpage, you can select a state and parameter of interest: www.nrcs.usda.gov/wps/portal/wcc/home/snowClimateMonitoring/30YearNormals

The Interactive Map also provides the ability to view the normals by major river basin in each state. Here’s a link to the map showing just Utah and Nevada, but any state can be selected in the Map Controls on the right side of the map. You can compare the normals between the current reference period and past normals by clicking the 1991-2020 vs 1981-2010 Normals link in each basin pop-up.

SSWSF staff in Utah and Nevada have each put together some really nice documentation on the new normals in their respective states.

Utah: www.nrcs.usda.gov/wps/portal/nrcs/detail/ut/snow/waterproducts/?cid=NRCSEPRD1836038

Nevada: www.nrcs.usda.gov/wps/portal/nrcs/detail/nv/snow/products/?cid=NRCSEPRD1848428

Nick J. Canata
Dec 15, 2021

Would it be possible to get the snow pack for just the San Joaquin Valley of California.

Ben Weaver
Dec 17, 2021

@Nick J. Canata - thank you for your comment. Most snow stations in the San Joaquin are managed by the California Cooperative Snow Surveys: cdec.water.ca.gov/reportapp/javareports?name=PAGE6.

We do present this snowpack information on the NRCS Interactive Map. Here is a link to the Interactive Map showing the San Joaquin. The date of interest can be changed in the Map Controls on the right side of the map. Normals can be viewed by clicking the 1991-2020 vs. 1981-2010 Normals link in the basin pop-up.

Bill Howland
Dec 16, 2021

I think you should allow viewers to easily view plots of the older (i.e., historical), 10-year median data groups so we can see how far the dates for peak SWE totals are shifting each decade due to climate change.

Ben Weaver
Dec 17, 2021

@Bill Howland - thank you for your comment. While we do not show the shift in peak SWE from decade to decade, we do have plots of how the 1981-2010 and 1991-2020 median SWE are different for basin and station data. These can be accessed by clicking on the 1991-2020 vs 1981-2010 Normals link in the basin or station pop-ups on our Interactive Map. However, keep in mind that the calculation methods are different between the two reference periods so a direct comparison is not advised.

Carrie McLeod
Dec 17, 2021

This is great news for California. Keep telling the positive mother nature stories!!

We need to conserve rain water more in these wet climates.

Laura Lundquist
Dec 20, 2021

Rather than using a sliding 30-year average, which is obviously going to decrease due to dwindling snowpack, why not keep the information you have and just add the new decade? Rather than using 1980-2010, use 1980-2020. This would still cause the average to decrease but would give a better idea of what is actually happening to the snowpack, information that water users actually need.