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London, Middlesex County under frost advisory as overnight low set to hit zero

Click to play video 'How gardeners can protect plants against frost' How gardeners can protect plants against frost
From the archives: Tips for gardeners as frost arrives in Edmonton, including which plants are susceptible to an overnight freeze and and which can last for a few more weeks. – Sep 15, 2020

It’s almost three weeks early, but Environment Canada has issued a frost advisory for London and Middlesex County, as well as a large swath of southern Ontario.

The national weather agency says the overnight low is expected to fall to 0 C on Friday night into Saturday morning and again on Saturday into Sunday morning.

Read more: ‘Unseasonably cool’: Frost advisory issued for parts of Saskatchewan

The advisories are issued during the growing season to alert the public that temperatures may reach the freezing mark and could result in damage to plants and crops.

The City of London falls within Zone C of the Climate Zone Map of Ontario, with the first frost coming Oct. 8 on average, based on data from 1976-2005.

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The overnight low had set a new record for London. Forecasters say the temperature fell to 0.6 C, which beat the previous record low of 1.7 C set in 1973.

Anthony Farnell, chief meteorologist for Global News, says the early frost doesn’t necessarily mean an early winter.

“Tuesday, Wednesday, we’re back up into the 20s. So if you can somehow manage to withstand the next two nights — because the next two nights are going to be cold — then I think you’re going to have another long stretch that’s going to take you likely through the rest of September above zero.”

Farnell says the low temperatures are thanks to an area of high pressure coming from the far north of Canada but it’s also helping to clear the sky.

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Read more: How the U.S. wildfires are impacting air quality from B.C. to Ontario

“The blue skies are back after what was a week of haziness and smoke from those western fires. So at least that’s the good news, the air is clear once again, but it’s those clear skies and low humidity levels and tonight, light wind, that really affect the valley locations most,” he explained.

“Cold air likes to sink down to the lowest points around. So if you’re typically prone to frost, you’re going to probably see it tonight. And maybe if you’re in the middle of, say, downtown London, you may just get off with temperatures slightly above zero.”

As for the long-term forecast, Farnell expects above-normal temperatures throughout October and into November.