While our growing season ends much earlier than the metro areas to our east, trends don’t show much variability from previous years along Interstate 95.
As we see fewer hours of sunlight, pumpkin spice and chilly mornings are on the minds of many folks. This leads to talk of the end of the growing season with fall’s first hard freeze.
Every 10 years, the 30-year climate averages get updated by the National Oceanic and Atmospheric Administration. The current 1991-2020 dataset has been used for a few years, but just early this month, the Sterling, Va., Weather Service updated the median date (date in the middle of the dataset) for the first hard frost of the season and spring’s last hard freeze date.
For Washington, D.C., the frost that ends the growing season occurs on or about November 1. This lines up with the first fall freeze date from the previous climate normal (1971-2000) of October 29 to November 5. In Baltimore, the median date for the season’s first hard frost is also November 1. This hasn’t changed much from 20 years ago when the date was October 29 to November 5.
The National Weather Service will put out Freeze Watches and Warnings until the first hard freeze occurs, which happens on clear, calm nights with temperatures of 28 degrees or colder. Temperatures this cold end the growing season for even hearty plants.
There is a fly in the ointment. In the event of a warm late fall season, if we don’t see a killing frost by November 15, the weather service will declare the growing season over. This happens by default because all vegetation becomes dormant thanks to lack of sunlight that shuts down the photosynthesis process in plants. So, Freeze Watches and Warnings will not be issued after November 15 even if the temperature drops for the first time of the fall season to 28 degrees or colder.
The median date for the last spring freeze in Washington and Baltimore is April 11. Typically, after this date, vegetation is in bloom and temperatures at or below 28 degrees would be detrimental to their development for the growing season.
While we have chilly temperatures in the forecast on occasion through the next two weeks, the Interstate 95 corridor is not expected to see a killing frost.
