Frost advisories mark return of cold weather

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Frost advisories from Environment Canada warn the heat of summer is behind us in Rocky View County (RVC). Much of Alberta to the north of Calgary, including RVC, were greeted by frost advisories Sept. 3 and 4.

“I think you can look at the patterns and say summer, as much as you don’t want to admit it, is essentially over, in terms of the meteorological patterns that we have,” said Dan Kulak, meteorologist with Environment Canada.

Kulak said RVC residents can expect to see swings in temperature from hot to cold as September progresses, and added it’s not unusual to get frost in early September.

“If we look back in the records for the Airdrie area… the earliest freezing temperature I can find in the record for the fall is Aug. 23, -0.7 degrees back in 1992,” Kulak said. “Really, from that point forward in our database, most of the record lows are on the minus side of zero.”

According to Kulak, due to the elevation of the prairie communities surrounding Calgary, nights in September tend to cool significantly as colder air from the north moves into the region.

“It’s a prelude of what’s to come in the winter time,” he said. “I still think we have some reasonably summer-like days left in store.”

Frost advisories are issued when there is a significant likelihood of temperatures dropping to or below freezing. These advisories may not necessarily forecast visible frost, Kulak said, but actually indicate that temperatures at thermometer height – about 1.5 meters – will drop below freezing, with temperatures directly at ground level dipping even a few degrees colder.

“You can have freezing temperatures without visible frost actually forming on your plants,” he said.

When frost is in the forecast, greenthumbs will want to take steps to protect their plants. Scott Stoner, horticulturalist with Blue Grass Nursery, Sod & Garden Centre, said spraying plants with an insecticide and bringing them into the house can help keep the plants alive.

“You’ll want to do it when it’s still nice out,” he said. “Spray the plants down, top to bottom, and let them drip dry, and then bring them into the house.”

Stoner said, unfortunately, frost spells the end for outdoor plants and gardens. Covering plants when it gets cold can extend their lives a little, he added, but a hard frost will eventually kill them.

Harry Brook, crop specialist with Alberta Agriculture at the Ag Info Centre, said frost can be frustrating to agriculture producers as they try to harvest this time of year.

“The biggest problem with frost and the harvest is it can severely downgrade your crop,” he said. “If you have a late crop that was seeded, it can also affect your yield.”

According to Brook, this year’s frosts are coming earlier than last year’s. In 2017, killing frosts of -4 degrees didn’t impact crops until October. This year – while RVC has not yet been affected – killing frosts have already swept the Peace region and elsewhere. Those killing frosts can damage the quality of the crop, which makes it more difficult to find a market to sell to.

“If you know that the likelihood of a killing frost is a few days ahead, you can actually swath a crop and put it in the swath with the hopes you have three or four days of dry weather,” he said. “A lot of times, you don’t get that sort of advanced warning, so you’re sort of at the whim of the weather.”

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