Moose Jaw and most of southern Saskatchewan have been covered in a haze of fog for most of this week.
The lingering fog is due to the warmer-than-average temperatures and the lack of weather systems. In turn, this has caused the weather patterns over the prairies to become stagnant.
“What happens is when there are no winds around to stir up the lower atmosphere, we get what’s called an inversion over the prairies and can happen in valleys, which we know is where Moose Jaw is,” says Environment Canada Meteorologist, Terri Lang.
“An inversion means that the air isn’t moving through the lower atmosphere and is trapped by this cap in the atmosphere. That traps all the moisture that is around from open rivers, along with moisture sources from factories and houses. All the pollutants get trapped under this inversion and we start getting fog development,” adds Lang.
The basis around how fog is formed is an influx of moisture in the air from houses, rivers, lakes, factories, and pollutants, along with mild temperatures.
Fog is made up of tiny water particles that linger in the air and attach themselves to objects such as trees, roads, and even your car.
When those fog particles attach themselves to a below-freezing object, it creates what’s called rime-icing, which Moose Jaw residents may have noticed around the city this week.
Lang says that rime-icing can survive in liquid form in temperatures up to –25 degrees Celsius.
“What happens is when you drive through the fog or the fog drifts past the trees, buildings, powerlines or your car, the moisture gets deposited directly onto these things and we get a build-up of rime-icing.”
A common misconception about rime-icing is that people mistake it for hoarfrost. Hoarfrost is created under clear skies, is lighter and is not as dangerous.
Rime-icing on the other hand can be very dangerous, as it can build up a lot quicker than frost.
“It is liquid freezing onto below-freezing objects and tends to be heavier and denser, which can create slick conditions on the road but it can also weigh down those powerlines.”
She spoke about an event about four years ago where a build-up of rime-icing on the powerlines led to a massive outage across southern Saskatchewan.
The one positive of rime-icing Lang says is that it makes for a great photo opportunity.
“It’s so beautiful and delicate, you can see each of the individual droplets and how they have formed into these very delicate structures. It’s beautiful but also quite dangerous.
The fog-like conditions that Moose Jaw has seen this past week have been the perfect breeding grounds for rime-icing such as lots of moisture, below-freezing temperatures, and lots of clouds.
There are two kinds of rime-icing – soft and hard rime. Soft rime is less dense, is milky and crystalline, like sugar, and appears similar to hoar frost. Hard rime is less milky, especially if it is not heavy.