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Products Log

Date Description
5/10/2010 Version 3 of the 800 meter PRISM Normals data set for the conterminous United States is now available. Changes include improvements to the station period averaging scheme, and minor model parameterizations. The older Version 2 data set is still available from our ftp server at this link.
5/4/2007 5/3/07. Version 2 of the 800-m PRISM data set for the conterminous United States is now available. Improvements over Version 1 include eliminating several bad station values, fixing a missing row in the precipitation grid along the US Canada border in the western US, and improved inversion height and topographic index grids. Version 2 data are now available from the standard PRISM Data Matrix. The older Version 1 is still available on our ftp server, however, and can be accessed here.
8/15/2006 Starting with the August 2006 monthly update, new 4km resolution 1971-2000 climatologies were created for precipitation, average maximum temperature, and average minimum temperature. These climatologies were derived from the 30 arc-second climatologies. Also note, as in the past, that these climatologies are used as the predictor grids for the 4km monthly updates.
6/27/2006 If you have downloaded the new 30-second tmax and tmin grids for the US since they were made available in May 2006, please re-download these data sets. Some post-processing inconsistencies were found in these files. The corrected data sets (now available) show small changes to a few of the grid cell temperature values, up to 0.5C in magnitude, confined mainly to high-gradient and coastal areas
3/11/2005 A year ago (see 3/5/2004 entry), we lamented the fact that the ASOS observing system badly underestimates snowfall. Since then, we have been looking for replacement data, especially in Minnesota. Thanks to data compiled by the Minnesota State Climatology Office, we are now able to replace the underestimated ASOS precipitation observations with “augmented” observations for many stations in the state. In addition, we are including precipitation data from the Minnesota High-Density Network, which adds valuable (and reasonable) observations for many more sites. Now, we just need to find similar data sources for other northern-tier states!
7/6/04 Feedback on our SPI products indicated that there was uncertainty about some of the patterns in the longer durations, especially in the West. We agreed with this assessment, and performed an investigation. We found that some of these patterns were apparently caused by artifacts produced by a change in the way the precipitation grids were created that began in 1997. Fixing this will entail creating a new set of monthly grids for the entire 1895-present period. This will take some time. For now we will update all our usual products, except SPI. SPI will be updated as soon as we feel known artifacts in the grids have been minimized. Thanks for your comments!
7/1/2004 As was described in the previous entry, ASOS chronically under-reports frozen precipitation. We are attempting to reduce our dependence on ASOS precipitation data for mapping the month just ended by using a hydrologic data set made available to NCEP by the NWS River Forecast Centers. This data set includes a number of networks, including:
  1. Municipal ALERT (Automated Local Evaluation in Real Time),
  2. GOES DCP (Data Collection Platforms),
  3. MESONET,
  4. LARC reports (Limited Area Remote Collectors), and
  5. some USFS/BLM RAWS (Remote Automatic Weather Station) data.
The increased station density is a clear improvement in states such as Oklahoma, where the Oklahoma Mesonet is now included. However, the hydrologic data set includes many ASOS observations, resulting in little improvement over the northern tier of states in winter. It is not until the COOP provisional data for the central and eastern US are added one month later do we see a marked increase in observed precipitation in these areas. We are now working with the Western Regional Climate Center to determine whether any COOP data for the central and eastern states can be made available one month earlier, so as to reduce our need for ASOS observations. A web document describing how the precipitation map for January 2004 changes as data sources and density change over time is available here
6/27/04 An experimental version of SPI (Standardized Precipitation Index) is now available. It includes durations of 1 to 72 months. Your feedback is appreciated.
3/5/2004 It has come to our attention that ASOS, the National Weather Service’s (NWS) Automated Surface Observing System (ASOS), can sometimes underreport precipitation quite significantly. ASOS precipitation data are incorporated into our maps for the most recent two months or so, until they are replaced with NWS COOP (Cooperative Observer Program) data. We are working to find an alternate data source for the most recent months that is likely to be more representative of the COOP precipitation values, and will switch to that source as soon as possible. A log entry will be made when this has been implemented. Again, this ONLY affects precipitation maps and data for the most recent two months or so.
2/21/2004 All map graphics have been corrected to display American (English) units. Users can choose which units to display in time-series queries from the PRISM Explorer (mapserver) application.
2/10/2004 Sites map graphics have been added to indicate the locations of station data that were used to generate the gridded data and graphics.
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