If you have ever read that a city’s “average high in July is 89°F,” you have used a climate normal. But what exactly is being averaged, over what period, and how should you read the number? This guide explains NOAA’s 1991–2020 U.S. Climate Normals in plain language.
The answer first
A climate normal is the average of a weather measurement — temperature, precipitation, snowfall — taken at one weather station over a fixed 30-year window. NOAA’s current normals cover 1991 to 2020. They are recalculated roughly once a decade. Normals describe what is typical, so they are ideal for planning (“when is it usually warm and dry there?”) but they are not a forecast of any particular day.
Why 30 years, and why 1991–2020?
Thirty years is the period the World Meteorological Organization recommends: long enough to smooth out year-to-year swings (a hot summer here, a wet winter there), short enough to reflect the recent climate. NOAA releases a new set at the start of each decade. The 1991–2020 normals were published in 2021 and replaced the older 1981–2010 set; the next will cover 2001–2030.
| Period | Released | Status |
|---|---|---|
| 1981–2010 | 2011 | Superseded |
| 1991–2020 | 2021 | Current |
| 2001–2030 | ~2031 | Future |
What gets measured
For each station, the normals include monthly and annual values such as:
- Average daily maximum (high) temperature — the typical warmest part of the day.
- Average daily minimum (low) temperature — the typical overnight low.
- Average total precipitation — rain plus melted snow, in inches.
- Average total snowfall — where snow falls, in inches.
On WeatherNormal, each city page shows all of these in a 12-month table. For how to interpret the high-versus-low gap, see how to read average high and low temperatures.
How to actually use them
Normals answer “what is the weather usually like?” — which is exactly what you want when picking travel dates months ahead. A few practical uses:
- Best time to visit. Find the months with comfortable average highs and below-average rain. We compute this on every city page; the rule is documented in our methodology.
- Comparing cities. Is Seattle really rainier than Miami? (By total inches, no — see the rainiest cities ranking.) Normals let you compare places on a level footing.
- Packing. Knowing the average high and rainfall for your month tells you roughly what to bring. Our packing & comfort tool does this automatically.
The one big caveat
A normal is an average, so a given day can land far from it. An “average July high of 89°F” might mean a string of 95°F afternoons and a few cool 80°F days. Normals also can’t capture humidity, wind or a freak storm. Treat them as the backdrop for planning, then check a live forecast close to your trip.
Where WeatherNormal’s numbers come from
Every figure on this site is a NOAA NCEI 1991–2020 normal, captured as a fixed dataset and verified per city against the published source. The data is a U.S. Government work in the public domain. See the methodology page for the stations used and our full sourcing notes.