NOAA’s National Weather Service (NWS) proposes updating precipitation frequency estimates for the states of Washington, Oregon, Idaho, Montana and Wyoming. The update will be published as a Volume of NOAA Atlas 14 “Precipitation-Frequency Atlas of the United States” on the web at www.nws.noaa.gov/ohd/hdsc. The link above shows states that have already been updated. The results are published in NOAA Atlas 14 Volume 1 to Volume 9. A project to prepare a volume for the northeastern states of ME, VT, NH, NY, MA, CT, and RI is underway and due for completion in 2015. The new NOAA Atlas 14 estimates are greatly improved in terms of accuracy, reliability and resolution. They are derived using improved data in terms of both period of record and station density, state of the art statistical techniques, and a new approach to spatial interpolation that accounts for variation in terrain. The technologies used so far in NOAA Atlas 14 have been recognized as state of the art. Those technologies with potential improvements will be applied to the development of this volume.

The purpose of this study is to determine annual exceedance probabilities (AEP) and average recurrence intervals (ARI) for durations ranging from 5 minutes to 60 days and for ARIs from 1 to 1,000 years. The point estimates will be spatially interpolated to a spatial resolution of approximately 4km x 4 km. The study results will be published as volumes of NOAA Atlas 14, a wholly web based publication available at www.nws.noaa.gov/ohd/hdsc. The publication will include the artifacts provided in Volumes 1 and 2 including access through the Precipitation Frequency Data Server, base grids in standard formats, electronic copies of maps, and results of trend analyses, charts of seasonal distributions and probabilistic temporal distributions, and detailed documentation. Updated areal reduction factors are being developed as a separate appendix to NOAA Atlas 14 for the entire U.S. including Alaska. The project will review and process all reasonably available rainfall data. It is recognized that the rainfall data archived by NOAA's National Climatic Data Center (NCDC) may not be sufficient to accomplish the objectives of this project. Therefore, other data available from sources such as State Climatologists and other Federal, State and local agencies will be examined and included if appropriate. The state of the art techniques and processes developed and applied for NOAA Atlas 14 Volumes 1 to 10 will be applied. 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.

The attached proposed Statement of Work by NOAA provides detailed information on the following: Task 1 - Data Collection and Quality Control Task 2 - Regionalization Task 3 - Frequency Distribution Selection and Fitting Studies Task 4 - Frequency Calculations Task 5 - Short Duration Estimates Task 6 - Internal Consistency at Observing Locations Task 7 - Spatial Interpolation and Consistency Task 8 - Mapping and other Spatial Artifacts Task 9 - Temporal Distributions Task 10 - Peer Reviews Task 11 - Documentation Task 12 - Final Deliverables Task 13 - Status Reporting

Commitments required: $1,683,272 with the following estimates by States: ID ($234,019), OR ($374,558), WA ($306,952), MT ($457,885), WY ($309,858)