It’s been a stretch of above average temperatures and a protracted spell of fog to kick off 2023. While another system could move through at any time to change all that, meteorologist with Environment and Climate Change Canada Teri Lang says we can expect more of the same, at least in the near future.
“We’ve been running above average temperatures for this time of year,” Lang explains. “Usually our average highs are -14 with overnight lows about -24. That’s largely because of where the jet stream is sitting. There's one sitting to the north and one just to the south and that’s directing the weather traffic around us. We’re kind of in this middle ground.”
That middle ground is largely a stagnant air mass that’s produced little movement or wind. A southerly system trying to invade the air mass will bring along milder temperatures for the weekend, possibly into the plus values. Lang says it could also bring some precipitation along with it in the form of snow or freezing rain. The type of precipitation in store for east central Saskatchewan is largely dependent on the path of the incoming system.
“The weather models are trying to figure out whether it wants to head more through central Saskatchewan or southern Saskatchewan. If it takes a more southerly route, then there will be more in the way of snow. If it is more northerly, then that’s when the risk of freezing rain enters the equation.”
The stagnant air mass has led to a widespread thermal inversion that tends to trap warmer air and humidity closer to the ground. The phenomenon has triggered air quality statements for pollutants in large centres like Edmonton over the past week. It also traps humidity which, along with the temperature differential, has been giving the prairies its daily staple of fog. It’s painted trees, power poles and lines with a bright coat of rime icing, a cousin to hoarfrost. Hoarfrost, Lang says, occurs only under clear skies while fog, cloud and high humidity breed the heavier, opaque rime ice.
“What happens with rime icing is that all the tiny moisture particles we see as fog are actually in liquid form. They can stay in liquid form up to temperatures of -25 if you can believe it. Those round droplets are able to maintain their shape, but as soon as they hit something with the temperature well below freezing, it freezes instantly.”
Rime icing creates a heavier, thicker coating than hoarfrost. In situations like this January, the rime ice accumulates enough to weigh down tree limbs and power lines to the point where it can cause power outages with downed or disconnected lines.
“There’s actually a risk to it,” says Lang. “The other risk is that it freezes on the roads, so we tend to get slick surfaces because of the icing that’s coming out of the fog.”
Inevitably, the stagnant air mass will be pushed aside by a system strong enough to do so. In the meantime, enjoy the mild air and white winterscape, but take additional care motoring through the foggy mornings and evenings when wildlife is most active.