Wednesday, December 07, 2016

After the big dig, comes the big chill!

Residents of Winnipeg and southern Manitoba are digging out after a major winter storm brought heavy snow, high winds and blizzard conditions to much of the Red River valley Tuesday into Wednesday.  In Winnipeg, the storm dumped 25-35 cm of snow over the 2 days, with strong winds gusting to 70 km/h producing significant blowing and drifting snow. It was the city's worst winter storm in several years.. perhaps one of the worst since the blizzard of April 1997.  The storm was even worse outside the city as powerful winds of 70 to 80 km/h produced blizzard conditions over the western and southern RRV, leading to the closure of many highways including the TransCanada from Headingly to the SK border, Hwy 75 from Winnipeg to Emerson, as well as highways 2 and 3 southwest of the city. 

But now that the storm is ended, there's a new winter hazard to prepare for.. bitter cold. A massive Arctic airmass has settled in over western Canada, and this colder airmass will be be spreading into southern Manitoba over the next couple of days. By Friday, daytime highs are only expected to around -17C with lows in the minus 20s.  This will be the first time in 7 weeks that temperatures will be below normal in southern Manitoba. In Winnipeg for example, the average daily temperature has been above normal since Oct 21st, a streak of 48 straight days as of Dec 7th. This streak will come to an end Thursday as a new streak of below normal temperatures begins. Temperatures will remain well below normal through the weekend into next week, with even colder air moving in for mid week next week. Temperatures may dip to -30C or lower by Dec 14th, mid winter cold we haven't experienced since last winter.   So break out the parkas and get those block heaters ready..  much colder weather is on the way! 

1 comment:

  1. You'll be hearing a lot about windchill in the next few days.. so it's a good time to remind people what windchill actually is.

    As I always stress every winter, windchill is NOT an actual temperature. It's a number that tries to approximate an equivalent COOLING RATE that our bodies experience based on the actual air temperature and wind speed. So, when you hear that the temperature is -20C with a windchill of -35, it does not mean it's -35C outside. It means that because of the wind, your body will lose heat at -20C at the same rate as if the air temperature was -35C with no wind. Wind accelerates heat loss from the body. The stronger the wind, the greater the rate of heat loss.. so the colder it FEELS to the human body. But the air temperature is always the air temperature... it's never what the windchill says it is.

    Note also that you need a certain amount of wind to start accelerating heat loss from the body. Generally, you need at least 13 km/h of wind or more to start this heat loss from the body. If the wind speed is under 13 km/h, your body's thermal layer around the skin will generally be enough to combat any heat loss due to the wind. So windchill is pretty much a non-issue if the wind speed is under 13 km/h. Quoting windchill values when the wind speed is less than 13 km/h gives an exaggerated windchill, and is misleading. Your body will generally keep you insulated at light wind speeds.

    Note also that windchill values in Environment Canada forecasts are the LOWEST expected windchill during that part period of the forecast. It does not mean the windchill will be that value the entire time. So for example, if the daytime high is -18C but the morning low is -27C with a -35C windchill.. the forecast windchill for the day will say -35, even though the windchill in the afternoon will be more like -25. The lowest windchills are usually first thing in the morning when temperatures are coldest. Of course, if the wind speed increases during the day, then windchill values can be as low or lower than the morning. Click on EC's "24 hour forecast" to see how windchill values change on a hourly basis.