It's Time to Start Thinking About First Freeze Dates Across the US!
by Stephen Strum, on Sep 19, 2018 2:04:50 PM
The date of the first fall freeze varies widely across the US, with frosts and freezes often seen by mid-September across the Rockies and northern tier of the US, but sometimes not until December along the Gulf Coast.
The map below from the Midwest Regional Climate Center shows the median date for the first freeze across the US. Across the Dakotas, Minnesota, northern Wisconsin and northern New England, the first freeze of the season is typically seen during the second half of September. Areas from Kansas to the Ohio Valley usually see the first freeze occur during mid-to-late October, while the first freeze doesn’t often happen across most of Texas and the Gulf Coast until November or even December in some years. Also notice that while much of the Appalachians frequently see a freeze during October, the immediate East Coast as far north as New York City doesn’t see a freeze until November, on average. That is the result of both the warming influence of the Atlantic Ocean as well as the urban heat islands of the major coastal cities.
I took a deeper dive into the data and produced the following plot of first freeze dates by city. The bar for each city shows the range of dates for the first freeze in light blue, while the gray portion of the bar indicates the period within one standard deviation of the mean first freeze date. A blue line denotes the actual average first freeze date in the middle of the gray portion of the bar. Note that data for the period 1981-2017 was used to produce this chart.
While the date of the first fall freeze will vary significantly from year-to-year, if you live in Bismarck, Denver, or Great Falls you can be assured that you will see a freeze before folks in Dallas or New York City do.