NOAA Atlas 14 is the authoritative source for precipitation frequency information; used in flood risk management and infrastructure design

NOAA’s National Weather Service has updated Atlas 14 with Volume 12, covering Idaho, Montana and Wyoming. Volume 12 covers a range of storm durations, from 5 minutes to 60 days, and average annual recurrence intervals of one year through 1,000 years.

Developed by the National Weather Service’s Office of Water Prediction, Atlas 14 is the federal standard and authoritative source of precipitation frequency data and is derived from an analysis of historical precipitation data to predict the likelihood of observing a precipitation event, at a specified location in any given year, under the assumption of a stationary climate. 

Data from this volume and Atlas 14 as a whole are used for engineering planning and design of infrastructure, such as culverts and roadways nationwide, under federal, state and local regulations. These estimates help delineate flood risks, manage development in floodplains for FEMA’s National Flood Insurance Program, and are used to monitor extreme precipitation observations and forecasts. 

Volume 12 - last updated in 1973 - can now help more precisely answer questions about how common a given rainfall total is over a specified amount of time in a particular location and provide more precise information about 100-year storm events in these three states.

Map showing differences in 100-year 6-hour estimates (in inches) between NOAA Atlas 14 (NA14) and NOAA Atlas 2 (NA2) for the Interior Northwest. Areas in green represent locations where NOAA Atlas 14 values are higher than NOAA Atlas 2. Areas in orange represent locations where NOAA Atlas 14 values are lower than NOAA Atlas 2. Credit: NOAA’s Office of Water Prediction.

In parallel to the Atlas 14 updates, NOAA is also developing NOAA Atlas 15 nationwide to incorporate climate trends. An Atlas 15 pilot project for Montana will be released later this month as a first look. The release of Atlas 15 pilot data is intended for comparison and feedback purposes as it has not completed the peer review process.

“NOAA’s precipitation frequency program has provided a core fundamental service and value to stakeholders for decades,” said Ed Clark, director of the NOAA’s National Water Center. “Through Atlas 14 updates and the development of the upcoming Atlas 15, NOAA will help inform how communities design their infrastructure to become climate resilient.”

NOAA’s Atlas 14 is a peer-reviewed publication. The new estimates can be viewed online or downloaded from the NOAA Precipitation Frequency Data Server. A detailed report is also available with further information.

Media Contact: Michael Musher, NWS Public Affairs, michael.musher@noaa.gov