Temperatures dipped below 40 overnight. When can Whatcom expect its first frost?
Chilly weather is in the forecast for Whatcom County, and the temperature dipped below 40 degrees for the first time since May on Thursday, Oct. 7.
And it’s going to keep getting colder.
“The great October slide has begun. The day-to-day average temperature falls more in October than any other month,” the National Weather Service in Seattle tweeted Oct. 7.
Average daily high temperatures plunge 9 degrees in 30 days — from 64 on Oct. 1 to 55 on Oct. 31, according to weather data recorded at Bellingham International Airport.
That could be the cue for backyard gardeners to finish their harvest, according to the National Weather Service in Seattle.
“First freeze of the season possible Tuesday morning, mainly across Thurston and Lewis counties,” the agency tweeted Thursday, Oct. 7.
Up to 2 inches of snow is in the forecast Saturday at levels of 3,000-4,000 feet — which is about the elevation of the North Cascades foothills village of Glacier in Whatcom County.
“(But) it won’t be just the mountains that feel the chill,” the weather service tweeted. “By Tuesday morning, temperatures could be around the freezing point for spots like Olympia and Shelton as well as other outlying areas. Time to make plans to bring any temperature-sensitive plants and pets inside.”
Bellingham’s low temperature will be 39 degrees, according to the current forecast.
First frost
On average, Bellingham sees its first fall frost on Oct. 29 and its last spring frost on April 5, according to the Old Farmers Almanac.
Frost occurs when temperatures reach freezing, or 32 degrees.
Because air is colder near the ground, frost could occur when temperatures are slightly warmer.
A frost date is the average date of the last light freeze in spring or the first light freeze in fall.
“Always keep an eye on your local weather forecast and plan to protect tender plants accordingly,” said the reference book, which began publication in 1792. “Weather, topography, and microclimates may also cause considerable variations in the occurrence of frost in your garden.”
Freeze temperatures are classified by their effect on plants:
▪ Light freeze: 29-32 degrees, tender plants die.
▪ Moderate freeze: 25-28 degrees, widely destructive to most vegetation.
▪ Severe freeze: 24 and below, heavy damage to most garden plants.
Frost dates an estimate based on data from the NOAA National Centers for Environmental Information, and the probability of a frost occurring after the spring frost date or before the fall frost date is 30%, the almanac said.
According to the popular online gardening site Dave’s Garden, the average risk of frost for Bellingham is from Oct. 18 through April 19.
“Almost certainly, however, you will receive frost from November 1 through April 3,” Dave’s Garden said. “You are almost guaranteed that you will not get frost from May 4 through October 4.”
