An Arctic airmass has left bitterly cold weather over southern Manitoba on Monday and put it under an extreme windchill warning.

Windchills of –40 C to –45 C means exposed skin can freeze in less than 10 minutes.

The windchill became less extreme on Monday afternoon, but very cold temperatures are expected to continue all day and into the evening.

The mercury hit –33.1 C between 9 p.m. and 10 p.m. on Sunday, making it the coldest temperature in Winnipeg since Jan. 30, 2011, when it was –34.7 C, says CBC News meteorologist John Sauder.

In Winnipeg, the daytime highs for the next week are not expected to get any warmer than –20 C, and reaching only –26 C on Wednesday. Overnight lows will hover around the –30 C mark.

Temperatures were so harsh, they prevented Canada Post from getting mail out to thousands of Winnipeggers.

Areas highlighted in red are the ones under an extreme windchill warning. (Environment Canada)

Canada Post advised said about 18,000 addresses in Winnipeg would not receive mail on Monday. A spokesperson said normal mail delivery would resume when the weather improved.

"Sometimes on days like this, when vehicles can't get started and we can't get people out to the routes on time, we just have a delay that we can't handle," spokesperson John Caines told CBC News.

"Unfortunately, that's what happened today, and maybe tomorrow the vehicles will be starting better and we'll be back on track."

Caines said many of the mail delivery vehicles that would not start on Monday had been plugged in the night before.

"We're having trouble with the ones on the road, too, where the fuel lines are gelling up because of the frost and the condensation," he added.

Caines said residents across the city are affected, but the backed-up mail will be delivered on Tuesday.

Homeless shelters feeling strain

The cold has also put an extreme strain in Winnipeg's homeless shelters.

The Salvation Army opened 35 cold weather beds after their regular beds filled up Sunday night.

Maj. Chris Dickens said they put down temporary beds everywhere from the kitchenette to the staff dining room to accommodate people.

Staff have also been busy making sure people have a warm breakfast before they go out.

"We had over 200 for breakfast and you know, there's no [extra funding] for that, but it's better for people to leave with a warm meal in their belly than to leave with an empty stomach," he said.

Furnace companies have also been busier than usual.

Gord Caron at Winnipeg Supply said the company serviced about 40 customers over the weekend. That's double the amount of business they normally see this time of the year.

"You start getting into high –30s, –40s, pipes frost up. It's just a little bit extreme; a little too extreme," he said.

Caron says the wait for service is just over an hour. Other, smaller furnace companies, are reporting a 3 ½ to four hour wait.

The wait is a long one for battery boosts as well. More than 1,000 people have called CAA looking for a little help to get their cars going.

Plug-in warning

Despite the number of cars in need of a boost, Winnipeg’s fire paramedic service is warning motorists it’s not always best to plug in their vehicles inside garages.

Rick Stephanchew, a public information officer with the service, said cars that are kept inside garages should not be plugged in.

Stephanchew said a number of fires begin in garages from faulty extension cords, and they can be particularly dangerous in attached garages.

"It’s nice to have them in the garage — out of the wind — and usually if they have a strong battery, you know, the car should start," said Stephanchew.

Stephanchew also advised homeowners to keep a watchful eye on space heaters. He said they should not be used in rooms where people are sleeping, and they should be turned off before leaving a room.

"They should be used sparingly, when people are in a room with a space heater and awake," he said.

He added the appliances draw a lot of electricity and should never be used with extension cords.