Atlas 14 and Atlas 15
NOAA identifies Atlas 14 as the current precipitation frequency standard while Atlas 15 is being developed to supersede it after publication.
RainYard Tools
Rainfall data
Design Storm Cheat Sheet
A plain-English guide to rainfall depth, intensity, return periods, and when to use local data.
TermPlain meaning
Rainfall depthTotal rain for a storm, such as 1.0 inch.
Rainfall intensityHow fast rain falls, such as 2.5 inches per hour.
Return periodA probability label, not a schedule.
OverflowThe route water takes after storage is full.
A practical homeowner starting point
For small unregulated projects, 1 inch is a useful screen. For permits, use the rainfall depth required by the local stormwater manual.
Questions
Common checks.
Is a 100-year storm once every 100 years?
No. It is a probability label, not a schedule.
Should I use depth or intensity?
Storage tools use total depth. Gutter and flow tools often use intensity.
Where do I get local rainfall data?
Start with local stormwater rules. NOAA precipitation frequency tools are the common national source.
Helpful referencesNOAA Atlas 15 informationNOAA precipitation frequency data