On October 1, 2021 the NRCS updated its 30-year normals period from 1981-2010 to 1991-2020. The NRCS uses normals in a variety of products to represent data as a percent of normal. Changing normals impacts percentages and requires users to re-calibrate themselves.
The following data types have normals:
Daily and Monthly SNOTEL Snow Water & Accumulated Precipitation
A Technical Summary about the new normals is available from the National Water and Climate Center.
Overview Presentation
The following video presentation highlights how the normals update impacts Nevada. For a pdf of the presentation slides click here.
Key Points about 1991-2020 Normals in Nevada:
The median is the new default normal used in all NRCS products.
Most 1991-2020 medians for snow, precipitation and streamflow in Nevada are less than 1981-2010 normals (exceptions exist).
The main impact of a smaller normal is it produces a larger percentage.
The reason 1991-2020 medians are less than the 1981-2010 normals is due to a combination of shifting the climate periods (1981-2010 to 1991-2020) and the statistical change from average to median.
Streamflow forecasts have been re-calibrated with 1991-2020 data.
New medians do NOT change SNOTEL data collection methods.
Tips for Adjusting to New 1991-2020 Medians
Pay attention to how percentages are reported – median vs. average. External sources may mis-label data.
Don’t expect as much water from a given percentage snowpack.
Think like a water manager. Concentrate on streamflow volumes not on percentages.
Investigate the new normals yourself using the tools lower on this page.
Use tools that compare current data with historic years without percentages. Examples include:
This Technical Summary of 1990-2020 Normals was produced by National Water and Climate Center and explains calculation methods and additional information.
Basin Snow Water Normals Comparison
Basin Precipitation Normals Comparison
SNOTEL Snow & Precipitation Normals Comparison
April-July Streamflow Normals Comparison
For help accessing historic time series and histogram plots click here.