What's new at PRISM

This information offers a "provisional" version of data from the past few months, and should be used cautiously. The information is based on whatever data is available from as many of the station networks and data sources as possible, so it changes as new data becomes available or as data quality is improved. The datasets are modeled using climatologically-aided interpolation (CAI), which uses the long-term average pattern (i.e., the 30-year normals) as first-guess of the spatial pattern of climatic conditions for a given month or day. CAI is robust to wide variations in station data density, which is necessary when modeling long time series. See PRISM datasets for more information; data available from this page is type "AN" (monthly and daily). For information on when the grids were most recently updated, see calendar of PRISM data updates.

The datasets are available based on either monthly or daily modeling. As with any averaging technique, our monthly value may not exactly match those you obtain by averaging daily values. Moreover, the precipitation observations used for daily modeling includes radar measurements, which monthly modeling does not take into account. These factors may cause dramatic local differences between the two datasets for a given month, particularly for areas east of the Rocky Mountains. Individual grids may also contain non-climatic variations due to station equipment and location changes, stations openings and closings, and varying observation times.

These datasets should be considered "provisional" (still likely to change as reporting stations finalize their information). After 6 complete months have elapsed, the observations are considered stable and datasets are stored in the "Recent Years" section.

Any known issues with the PRISM time series datasets are documented in the Known Issues section.