USCRN Implements New Approach to Precipitation

Photo of a USCRN precipitation gauge and shield

As seen in the center of this photo of the station near Redding, California, all USCRN sites are equipped with an all-weather, wind-shielded weighing precipitation gauge.

On August 17, 2015, the U.S. Climate Reference Network (USCRN) will change how it processes precipitation observations. The USCRN measures the state of the U.S. climate with a relatively small number of high-quality stations placed in representative environments with little likelihood for land-use change over the next 50 years.

Unlike other climate observing systems, USCRN stations perform three independent measurements of both air temperature and precipitation, which helps ensure continuity and high-quality data. However, this process makes calculating precipitation somewhat complicated because we must calculate one best precipitation amount from the three measurements for each five-minute interval and a separate measurement of the presence or absence of precipitation.

Therefore, we designed a new approach that better utilizes the information available, and we tested it exhaustively using real station data and artificial simulations. The new approach uses weighted averaging to extract the most common signal among the three individual automated measurements. Unlike the previous approach, which was somewhat too strict in guarding against errors, the new approach causes less loss of genuine precipitation. Overall, precipitation increased about 1.6% network-wide using the new approach, with significant improvements during light precipitation and at the beginning of heavier precipitation events.

While the processing of near-real-time precipitation observations will switch over on August 17, the USCRN saves all original observations used for making climatological calculations, so we will apply the new and improved approach to historical data for each station  back to2004–2005 when we installed the current five-minute observation interval.

Due to the millions of five-minute observations present in the USCRN database, we will not complete the historical reprocessing until the end of September 2015. After we complete the reprocessing, we will place an announcement at the top of the main USCRN web page. We will not only update the data in our database, but we will also update the quality-controlled datasets for their periods of record.

Please note that these changes affect only USCRN precipitation values. This is a small 134-station subset of thousands of stations used to calculate U.S. precipitation values, and the change should not have noticeable impacts on the general precipitation calculations in our monthly U.S. climate reports. However, these changes are important for the USCRN network and its user community.

For more information, please see:

To learn more about USCRN stations and their instrument suites, see Picture Climate: What’s a USCRN Station?