Back Home by Chris Hardie
Fall is in full swing with the trees changing colors but for me there is another annual event that is a stark reminder that winter is on the way – the first fall frost.
Based on annual statistics, the average first fall frost date for 44.1818° N and 91.1965° W (the coordinates of my farm) is about Oct. 1. There have been many years when fall frost fell into summer with September freezes and a surprise August freeze one summer in the late 1990s.
Even areas to the far north have enjoyed a warm fall so far. I was on a business trip to Cohasset, MN (which is 1.5 hours northwest of Superior, WI) in early October and the flowers there were still untouched by frost.
This year our last spring freeze was on May 14 and 12 days later we hit 90 degrees. As of this writing the National Weather Service has put my location under a frost advisory for overnight. If that occurs, we will have had a 143-day growing season, which is right on our average year.
The Old Farmer’s Almanac defines the temperature between 29 and 32 degrees as a light freeze, which will kill tender plants. A moderate freeze is between 25 and 28 degrees and anything below 25 is a killing frost.
There is a difference between the length of the growing season for the vegetable garden and the potted plants. What’s still alive among the weedy vegetable garden – there could be a couple baseball bat-sized zucchinis – will be mercifully euthanized.
But the forecast prompted my wife Sherry to issue a temporary evacuation order for the flowers and herbs planted in pots on our back porch. The order means that I carried the pots into the kitchen for a botanical sleepover. The pots will be returned to the porch for at least another week as the long-term forecast calls for overnights above freezing.
There are specific meteorological conditions that lead to frost. Clear skies lead to radiational cooling allowing heat to exit the atmosphere. Calm or light winds prevent atmospheric stirring and a thin layer of super-cooled temperatures develop at the surface, which is why you can have frost at the ground when air temperatures are above freezing.
Local topography also has a large role as the heavier cold air will settle into lower-lying valleys – which describes the location of our farm. Valleys also are sheltered from stronger winds, creating more frost potential.
The scientific explanation of the conditions for frost and forecasts are well and good, but sometimes you feel it in your bones. That’s not entirely true (especially in my two artificial hips), but there’s a feeling in the air and the look of the sky that stirs a primal instinct that tells you frost is coming. Either that or it’s a cramp.
There are plenty more lovely fall days to enjoy and we may even have a few more tastes of summer-like weather. Here’s hoping it’s later rather than sooner, but eventually the even more momentous annual event that marks the change in seasons will occur.
That event will be dependent on weather but more so on when sweaters and sweatpants simply don’t do the job anymore and the dial on the thermostat is turned to heat.
