Back in the fall, the National Oceanic and Atmospheric Administration’s (NOAA) Climate Prediction Center forecasted a warmer than average winter for most of the U.S. That got us thinking about how first frost has changed over the years, and how it will continue to evolve. Likely, a warmer winter means a later-than-normal first frost but is it the sign of a bigger climate trend or just a natural fluctuation?
When does first frost typically occur?
Of course, weather conditions throughout the year – variations in rainfall, hurricane activity, etc. – can affect the timing of first frost, but an article from The Weather Channel breaks down the average dates across the country by region. Northern parts of the country can experience first frost as early as September 15, while Southern California and the Southeast see their first frost around November 15, with the rest of the country falling somewhere in between those two months.
As an example, in fall 2019, South-Central Nebraska and North-Central Kansas experienced their first sub-freezing temperatures on October 11 and 12. At the time, the National Weather Service noted that the earliest frost/freeze recorded in those areas was September 3, 1974, more than a full month before the first frost timeframe for both 2019 and 2018.
How has first frost changed over time?
So, using the example above, is it just a coincidence that first frost in Nebraska and Kansas is happening later than it used to, or is it indicative of a bigger trend? The Environmental Protection Agency (EPA) charted changes in the length of the growing season in 48 states from 1895-2015. The research says, “The average length of the growing season in the contiguous 48 states has increased by nearly two weeks since the beginning of the 20th century. A particularly large and steady increase occurred over the last 30 years.”
The EPA also touches on the fact that the final spring frost is occurring earlier, resulting in an extended growing season. The report states, “In recent years, the final spring frost has been occurring earlier than at any point since 1895, and the first fall frost has been arriving later. Since 1980, the last spring frost has occurred an average of three days earlier than the long-term average, and the first fall frost has occurred about three days later.”
What does this mean for upcoming seasons?
For now, it seems as though first frost will continue to be a little later each year, meaning that average growing seasons will be longer; an outcome that has both pros and cons.
The EPA elaborates on this trend, saying, “A longer growing season could allow farmers to diversify crops or have multiple harvests from the same plot. However, it could also limit the types of crops grown, encourage invasive species or weed growth, or increase demand for irrigation. A longer growing season could also disrupt the function and structure of a region’s ecosystems and could, for example, alter the range and types of animal species in the area.”
It’s hard to predict how much first frost will continue to change over the next several decades and the results that will come from those changes, but we’ll continue to monitor these trends and keep you updated as more data becomes available.