By Chet Greason
Residents of St. Marys may have noticed a strange example of January weather on Monday, Jan. 22. In addition to rain, the area was treated to an unseasonal bout of thunder and lightning.
But Environment Canada’s senior climatologist David Phillips says January thunder, sometimes called “thunder snow,” is not as uncommon as it seems.
“It’s not as rare as you think,” he says, noting the St. Marys/London area usually averages about one instance of thunder snow per cold season (November to April). Some years, he says, there may be none at all; and oftentimes when thunder does roll in the dead of winter, residents either don’t notice because it occurs far up within the clouds, or they write it off as a passing train or rumbling transport truck.
Thunder snow occurs when warm air is pushed northward to our region, where it’s pushed further skyward by the cold air that is lingering close to the ground. This unstable atmosphere creates thunder and lightning, which is usually muffled by the clouds. Phillips says it’s more common in the Maritimes, and almost never occurs out west.
He remains unconcerned about Monday’s thunder snow, noting that no one was hurt.
“It’s more of a conversation piece than anything else,” he says.
Far more strange, he adds, has been January’s record-setting low temperatures coupled with an unusually high rate of thaws. He called the cold snap that happened over late December/early January “shocking,” likening both the freezing temperatures and the cold snap’s duration as more akin to the prairies.
“The pride in Ontario is that if you don’t like the weather out your front door, just look out your back door,” he says. “That’s how often we’re used to changes in the weather here.”
Locally, this January has been colder than normal. Phillips notes that, if you take the coldest January temperature taken in the London area last year, this past month has recorded a total of eleven days that were colder. But coupled with the plummeting mercury is a thaw cycle that’s in a state of relative overdrive.
Thaws are generally identified when the temperature goes above freezing, even if it’s by a fractional amount. January typically sees one, maybe two thaws locally; but this January has seen four and, according to Phillips, will likely see one more before February.
“That’s a bit unusual,” he says, calling it yo-yo or toilet seat weather given its propensity to going up and down. Phillips also calls it pothole weather, as it tends to wreak havoc with infrastructure. The warmth causes snow to melt, the water seeping down below the base of a road’s layer of asphalt. When that water freezes overnight or during a cold snap, it buckles and cracks the pavement.
He notes that the out of control freeze/thaw cycles have one upside, though.
“It’s great for maple syrup production!”
St. Marys director of public works, Jed Kelly, says he hasn’t noticed an unusually high rate of potholes yet. The town treats roads with a surface sealant that helps to prevent snow melt from seeping below the asphalt.
“I have noticed some cracks forming,” he said. “But I don’t think we’re that bad.”
Helping is a road salt truck that was repurposed last summer as a hot patch truck that mends roads. Kelly says that, should fair weather occur soon as forecasted, his department plans to do some road patching next week.
What he’s more concerned about is the stress that freeze/thaw cycles have on water mains, which can lead to burst pipes. A thick layer of snow tends to insulate underground infrastructure. Without it, the ground is prone to freezing solid, risking frozen and ruptured pipes.
“I hope it doesn’t happen, but it’s typical for that kind of weather,” he says.
As to the thunder snow, Kelly cites an old farm adage he was told recently: “Thunder out of season brings weather without reason.”
Phillips says the St. Marys area can expect one more warm, spring-like period before the end of January, whereas February is forecasted to be colder than normal with far less frequent thaws.
The upside? There will be more winter behind than ahead.
“Now truly is the dead of winter,” he says.
As to his prediction for a cold February, he adds one disclaimer.
“We’re not always right. I wouldn’t bet the farm on it,” he laughs. “But this is what our models tend to show.”