Meteorological fall began on September 1. It was warm early in the month, with highs over 100 degrees in many locations during Labor Day weekend. It has since turned more seasonable, with pleasant daytime temperatures, cool mornings, and, so far, no threat of cold air.
Nowhere in Kansas has there been any frost yet, but it was 39°F in Tribune and 40°F in Colby on the morning of the 12th, a harbinger of colder weather yet to come. The autumnal equinox, which marks the beginning of astronomical fall, was on Saturday, September 23, at 1:50 a.m. central time.
We will eventually experience a first frost and, in time, a first freeze, which can end the growing season, depending on how far below freezing the temperature gets and how many hours sub-freezing conditions persist.
Exactly when do the first frost and freeze typically occur in Kansas? In this report, we look at the average dates for those two significant cold weather events.
Data for 20 sites in Kansas were examined using the full period of record at each location. For this study, the first frost date is defined as the first occurrence of a temperature at or below 36°, and the first freeze is defined as the first occurrence of 32°F or colder. The dates that the first frost occurred each year were sorted from earliest to latest, and then the dates on which 10%, 20%, 30%, etc., of the first frost occurred on or before were identified (Table 1). This methodology was repeated for the first freeze data (Table 2). To see the data tables, go to www.cottonwood.ksu.edu.
Looking at the first frost date, the median date is in October, except for the far west and northwest areas of Kansas, where it occurs in late September. The median date is when there is a 50% chance of the first frost having already occurred. The earliest median date is in Oberlin (September 26), and the latest is in Wichita (October 18). Except for Wichita, there is a 10% probability of the first frost occurring before the first of October at all locations and a 90% probability that the first frost has occurred by the end of October.
There is a 60% or greater chance that the first freeze will occur by the end of October at all locations (Table 2), but the probabilities are higher for earlier dates in the west and north. As with the first frost date, Oberlin has the earliest median date (October 3), and Wichita has the latest date (October 28). September freezes happen occasionally, and occasionally, it’s November before the first freeze, but October is typically the month when the growing season ends. October is also when the normal lows each day decrease the fastest (Table 3); the daily normals drop by 11 to 14 degrees. By month’s end, Goodland, Oberlin, and Tribune all have normal lows below freezing. Only eastern and southern locations have normal lows in the 40s by October 31; all other locations have normal lows in the 30s.
Last year, the first freeze was in mid-October across the entire state, thanks to a cold air mass that invaded the state and brought widespread lows in the 20s, with a few upper teens. The first freeze in 2022 was on the 16th in Goodland, the 17th in Garden City and Hutchinson, and the 18th in Wichita and Parsons. For the northwest, this freeze was later than normal, but in the southeast, it was earlier than normal.
What about this year? It’s too soon to know, but the outlooks for the next two weeks favor above-normal temperatures, so it doesn’t appear that an early freeze will occur in September. As for October, we’ll have to wait and see. Until then, enjoy the pleasant fall weather!
Information and article provided by Matthew Sittel, Assistant State Climatologist, [email protected].
Stacy Campbell is a crop production extension agent in the Cottonwood District (which includes Barton and Ellis counties) for K-State Research and Extension.