Updating U.S. Precipitation Frequency Estimates for the Northwest

The purpose of this study is to determine precipitation frequency estimates for Idaho, Montana and other the Northwest States for durations of 5-minute through 60-day at average recurrence intervals (ARIs) of 1-year through 1,000-year. The estimates and associated bounds of 90% confidence intervals will be provided at 30 arc-sec resolution (approximately 800 x 800 m; varies with latitude). The study results will be published as volumes of National Oceanic and Atmospheric Administration (NOAA) Atlas 14, a wholly web based publication available at www.nws.noaa.gov/ohd/hdsc. The publication will include the artifacts provided in previous NOAA Atlas 14 Volumes, including access through the Precipitation Frequency Data Server, base grids in standard formats together with error estimates, electronic copies of maps, charts of seasonal distributions and probabilistic temporal distributions of heavy precipitation, and detailed documentation. Updated areal reduction factors, which are needed to calculate analogous areal precipitation frequency estimates, will be developed as a separate appendix to NOAA Atlas 14 for the entire U.S. They include regional frequency analysis based on L-moments including error estimates, a combination of PRISM based techniques and CRAB for spatial interpolation, techniques for the analysis of climatic trend, temporal distribution and seasonality, internal consistency checks and variety of automated processes designed to enhance productivity. Intermediate results in the form of hourly and daily estimates at several ARIs will be distributed for peer review as will the final documentation.


  • English


  • Status: Programmed
  • Funding: $640895
  • Contract Numbers:


  • Sponsor Organizations:

    Idaho Department of Transportation

    P.O. Box 7129
    3311 W. State Street
    Boise, ID  United States  83707-1129

    Montana Department of Transportation

    2701 Prospect Avenue
    P.O. Box 201001
    Helena, MT  United States  59620-1001
  • Managing Organizations:

    Federal Highway Administration

    1200 New Jersey Avenue, SE
    Washington, DC  United States  20590
  • Project Managers:

    Frye, Megan

  • Start Date: 20240315
  • Expected Completion Date: 0
  • Actual Completion Date: 0

Subject/Index Terms

Filing Info

  • Accession Number: 01741869
  • Record Type: Research project
  • Source Agency: Federal Highway Administration
  • Contract Numbers: TPF-5(454)
  • Created Date: Jun 3 2020 4:24PM