What Climate Normals Don't Tell You

Climate normals are 30-year averages. That's a powerful tool, but it hides three things.

One: year-to-year variability. Denver averages a May 10 last frost, but individual years have ranged from April 15 to May 31. The average is only a rough guide.

Two: extremes. A city's hottest day or biggest snowstorm doesn't appear in a monthly mean. For that, you need the all-time records page — every city on this site has one.

Three: trends. The current 1991-2020 normals are warmer than the previous 1981-2010 set. If you're planning for future decades, know that the recent normals are probably warming a bit every year, especially summer nights.