Office of the Washington State Climatologist

PNW Temperature, Precipitation, and SWE Trend Analysis Tool

Use the options below to analyze monthly temperature and precipitation trends around the Northwest using high quality data from the United States Historical Climatology Network (USHCN) version (through June 2021). This dataset has been adjusted for biases and inhomogeneities resulting from changes in the environment or operation of individual observing sites (e.g., urbanization, station moves, instrument upgrades, and time of observation changes). The procedure adjusts only the temperature data – the precipitation data are raw – so please use more caution when interpreting trends in precipitation. More information on the USHCN dataset can be found in Menne et al. 2009.

The map can also be used for analyzing snow water equivalent (SWE) totals (through 2021) for WA State only, which are recorded on the first day of each month (January, February, March, April, and May) from historical NRCS snow course locations. The earliest data from the manual snow course measurements begins in 1930 and most stations have the most complete data in April.

Please be advised that trends at a single location represent only that location, not necessarily a wide region, and are more susceptible to undocumented changes than when several stations are averaged together. For this reason, we encourage users to examine multiple time periods (i.e., “Year Range”) and stations, especially for the precipitation and SWE data. Questions regarding interpretation of the trends can be directed to OWSC.

Click on an individual circle for a time series graph of the selected station’s data. Multiple stations can be displayed at once. Hovering the mouse over the map brings up the following toolbar:

Additional guidance for using the tool can be found by hovering your mouse over the yellow question marks  embedded in the visualization below.