Maps of average temperatures in the USA

You may have seen the maps of monthly growth potential through the seasons from PACE Turf. Those animated maps take the average temperature, convert it to a growth potential, and then color code a map of the USA with that animation.

• Cool season (C3) grass growth potential through the seasons
• Warm season (C4) grass growth potential through the seasons

The PRISM Climate Group at Oregon State University have maps that cover temperature (and much more) at daily and annual and 30 year normal (climatological normals) time scales.

I like to consider a growth potential of about 10% as the time when the maintenance “season” starts in earnest. For cool-season grasses, the GP goes above 10% at an average air temperature of about 8 °C (46 °F). For warm-season grasses, the GP goes above 10% when the average air temperature is about 16 °C or 61 °F.

If we look at this map of climatological normal temperatures in the USA, it’s possible to track when the cool-season or warm-season maintenance season will start, on average. Follow the appropriately color coded region as it moves north in the spring and one sees when a cool-season or warm-season maintenance season will begin.

That was the climate. That’s what is normal, and that is useful for planning.

Then there is the weather, with a lot more variability. The animation below, also from PRISM, shows the daily average temperatures from April 1 to May 1 in 2024.

There are no more bands moving consistently north through the spring. The weather varies. On average, the temperatures will be like the climatological normals. But on a particular day, in a particular year, there can be a lot of variation from what’s normal.