Welcome to the NOAA Atlas 15 Informational Page

NOAA Atlas 15 is the new authoritative, spatially continuous National Precipitation Frequency Atlas of the United States, currently under development by the NOAA National Weather Service (NWS) Office of Water Prediction (OWP). As with previous Precipitation Frequency Atlases, NOAA Atlas 15 will provide spatially independent estimates of expected precipitation depth (or intensity) for a specified storm duration (e.g., 6 hours), at a particular location of interest (e.g., Tulsa, Oklahoma). The statistically expected precipitation estimates will be presented as exceedance probabilities ranging from 50% average annual exceedance to 0.1%, and will cover storm durations ranging from 5 minutes to 60 days. As an example, a NOAA Atlas 15 precipitation estimate with a 20% average annual exceedance probability has a 20% chance of being exceeded in the year of interest (see table below for a range of examples).

In contrast to NOAA Atlas 14, NOAA Atlas 15 will provide spatially continuous coverage over the entire United States and, for the first time, will also account for future temporal trends (through the year 2100). When published, NOAA Atlas 15 will be the authoritative source for precipitation frequency information across the United States. The current standard, NOAA Atlas 14, is referenced in many engineering design standards and floodplain regulations, published by entities outside of NOAA, and engineers and other practitioners use those standards and regulations to make local decisions (designs for drainage infrastructure, city and regional planning, etc.) Among the civil engineering community, precipitation frequency estimates for various durations are often referred to as Depth-Duration-Frequency (DDF) or Intensity-Duration-Frequency (IDF) curves.

NOAA Atlas 15 can help communities nationwide become more resilient when planning and designing new infrastructure. This objective will be supported by (1) the delivery of spatially continuous precipitation frequency estimates that cover the entire United States and (2) the incorporation of nonstationary statistical methods and information from climate models to account for future trends.

Although precipitation frequency estimates have existed for many decades (since the late 1930s) and have incrementally improved with advancements in data, science and technology, NOAA Atlas 15 represents a shift from a stationary assumption (i.e., extreme precipitation events do not change significantly over time) to a nonstationary assumption (i.e., extreme precipitation events change over time), a key modification that may impact the manner in which precipitation frequency information is applied.

As a provider of high quality scientific data, NOAA’s objective is to update national precipitation frequency estimates based on the best available and actionable science at the time of development. NOAA is committed to clearly describing the data that are generated, communicating how they were developed and providing widespread access to the information. As this dataset is used for a wide-range of applications, it will be up to users, organizations and government agencies to identify the appropriate bounds for the application of these estimates in the areas in which they have missions and expertise. To help with the transition from the current national standard, NOAA Atlas 14, to NOAA Atlas 15, NOAA plans to partner with several entities and to engage a wide range of stakeholders.

The United States Congress, through the Bipartisan Infrastructure Law (BIL), provided NOAA with funding to revise and update the current precipitation frequency standard, known as NOAA Atlas 14, and develop NOAA Atlas 15.

NOAA's Office of Water Prediction, which is part of NOAA's National Weather Service, is developing NOAA Atlas 15.

The NOAA Atlas 15 Pilot dataset would not have been possible without the support and contributions of grantees, contractors, and individuals from government, private industry, and academia.

NOAA Atlas 15 will consist of two volumes. NOAA Atlas 15 Volume 1 will provide a snapshot of current estimates that account for temporal changes in historical observations. When published, NOAA Atlas 15 Volume 1 will supersede the current NOAA Atlas 14 precipitation frequency estimates.

NOAA Atlas 15 Volume 2 will provide model-based precipitation frequency estimates projected into the future. Volume 2 estimates will be developed by applying adjustment factors to Volume 1 estimates (i.e. future relative changes obtained from downscaled climate model data).

All NOAA precipitation frequency standards will go through the public peer review process following the timeline presented below. Datasets will be released to the public at different points to ensure NOAA can collect feedback on NOAA Atlas 15, using NOAA’s service delivery model, as guidance.

• 2024 - Pilot project available for early feedback

• 2025 - Preliminary estimates available for peer review and feedback
• 2026 - Published estimates available for use and application

• 2026 - Preliminary estimates available for peer review and feedback
• 2027 - Published estimates available for use and application

In order to collect feedback early in the development process, NOAA released the NOAA Atlas 15 Pilot data over the state of Montana on September 26, 2024. With this early release, collaborative NOAA teams, including the National Centers for Environmental Information (NCEI), demonstrated to a large number of stakeholders the nature of the Atlas 15 data to ensure practitioners have the precipitation information they need, upon final publication.

The NOAA Atlas 15 Pilot covered estimates for a subset of storm durations (1 hour to 10 days) and average annual exceedance probabilities (50% to 1%), and was presented in two volumes.

The release of the NOAA Atlas 15 pilot data was intended for comparison and feedback purposes as it did not go through the peer review process. Both the data and web dissemination strategies are subject to change as a result of public feedback received and planned enhancements.

See the NWS Public Notification Statement announcing the NOAA Atlas 15 Pilot. The visualization tool developed for the NOAA Atlas 15 Pilot is available HERE.

NOAA released the Pilot data to facilitate understanding of the new framework, development process and methods as well as to provide early insights into the Web dissemination strategy. The Pilot data shared are not final, and may significantly differ from the data shared upon publication and full release. Some major differences are highlighted in the table below.

The NOAA Atlas 15 Pilot study only covers the state of Montana, whereas the NOAA Atlas 14, Volume 12 study spans the states of Montana, Idaho, and Wyoming. Moreover, the NOAA Atlas 15 Pilot implements nonstationary statistical methods and uses climate model information to project precipitation frequency estimates into the future. In contrast, the NOAA Atlas 14, Volume 12 study assumes stationarity when deriving precipitation frequency estimates. Though NOAA is working to implement NOAA Atlas 15, the NOAA Atlas 14 studies (Volumes 1 - 12) are the existing national standard and authoritative source for precipitation frequency information today. NOAA Atlas 14, Volume 12 data can be found on the NOAA National Weather Service Precipitation Frequency Data Server (PFDS).

NOAA will collect and review feedback on the NOAA Atlas 15 Pilot and consider refining its technical approach based on the feedback received. In 2025, NOAA plans to release preliminary NOAA Atlas 15 data for peer review for an area that covers the contiguous United States (i.e., the lower 48 states). The preliminary data and dissemination strategy for this dataset may reflect some of the feedback received during the NOAA Atlas 15 Pilot. See above for the full NOAA Atlas 15 timeline.

The Bipartisan Infrastructure Law provided NOAA with one-time federal funding to update precipitation frequency estimates nationwide while accounting for trends (i.e., NOAA Atlas 15). After completing peer review and upon publication in 2026 (contiguous United States) and 2027 (outside the contiguous United States), NOAA Atlas 15 will supersede NOAA Atlas 14 as the national standard and will become the authoritative source for precipitation frequency information across the United States.

NOAA Atlas 14 data can be accessed on the NOAA Precipitation Frequency Data Server (PFDS). Supporting documentation for NOAA Atlas 14 can be found HERE.

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