Climate MattersSeptember 9, 2015

Fall Temp & Precip Trends

Set 3 - Fall Temp & Precip Trends
Set 3

Fall brings colored leaves, pumpkin pies, and cooler nights. But falls are not as cool as they used to be. Our analysis this week indicates that fall temperatures have been climbing at a rate of 0.43°F per decade – a total of 1.9°F, on average, across the country. Closer inspection of the NCEI climate divisions shows that with little exception, the trend is for warmer falls in nearly every location.

As the concentration of greenhouse gases increases with deforestation and the burning of fossil fuels, the average global temperature continues to climb, and the planet is on track to have its hottest year on record (coming off a record hot year in 2014). That rise is reflected in the nationwide fall temperature trends.

The greatest fall warming is in the Plains and the Intermountain West. Parts of Arizona have warmed by as much as 3.5°F since 1970. But other parts of the country have warmed nearly as much – more than 3°F in parts of the Northeast.

Even though it hasn’t warmed as much in the Southeast, it has still warmed. Of the 343 climate divisions nationwide, only 4 show a cooling trend; those values were minimal and confined to parts of Georgia and South Carolina. In total, 98.8% of the climate divisions show a warming trend.

Precipitation trends are not as one-sided. Most of the Southeast coast and the Northeast have been getting wetter, but a broad area from the Upper Great Lakes and the Southern Plains through the Southwest have all gotten drier. Looking at the West Coast, only the Pacific coast of Washington State has gotten significantly wetter.

As warming continues in the coming decades, its effects will become more noticeable. Frosts and freezes will come later and be less frequent, possibly affecting the harvest season and food production. Wildfire season will likely be extended, and the fall foliage timing could shift for many locations.