TORONTO -- Powerful winds and an onslaught of snow slammed Newfoundland on Friday, shutting down roads and prompting St. John鈥檚 to declare a state of emergency.

In response, for large parts of the province, particularly in the southeast region of the island, which could see anywhere from 40 to 75 centimetres of snow.

And the federal agency doesn鈥檛 issue such warnings willy-nilly, according to senior climatologist David Phillips.

鈥淎 blizzard warning should scare people skinny,鈥� Phillips told CTVNews.ca in a phone interview on Thursday. 鈥淭here are specific criteria in terms of visibility, duration, cold, and whether it鈥檚 new snow or old snow.鈥�

For most parts of Canada, when winds of 40 kilometres per hour or more are expected to coincide with snow, reducing visibility to 400 metres or less.

Those conditions must be expected to last at least four hours for a warning to be issued, except for communities above the treeline, where conditions need to be expected to last at least six hours.

The purpose of official warnings is to urge people to adjust their behaviour in the event of a major weather event. In Newfoundland, residents are asked to consider postponing any non-essential travel. Power outages and building damage may occur, and people are asked to store any loose items left outdoors to prevent any injuries or damage.

Dozens of weather warnings were issued across Canada on Friday. Nearly the entire province of Alberta , with mid-afternoon temperatures in Calgary of -24 C expected to feel more like -35 C. Similar conditions were reported in Edmonton, with outdoor temperatures of -25 C feeling like -37 C. several coastal regions were under extreme cold and snowfall warnings.

When it comes to extreme cold warnings, different regions of Canada require thresholds, Phillip explained, because our relationships with winter weather vary from province to province.

鈥淚t comes down to the fact that people are better conditioned, better equipped, have better garments for handling those situations in Western Canada,鈥� he said.

鈥淲esterners think if winter can begin after Halloween, they鈥檝e won. We wait until December or January and think, 鈥極K, winter can start now.鈥欌��