By Jim Poling
Published Nov. 23, 2017
December looms on the late November horizon, leaving us wondering how it will treat us this year. Will it be cruel or will it be kind? It has been both in recent years.
Last December was a brute. It was slightly warmer than average but it snowed 27 of 31 days in Haliburton County. Snowfall totalled 134 centimetres, more than twice the average for December.
The year before that – 2015 – was extremely kind. It snowed on only 12 of the 31 December days, and measurable snow was recorded on the ground on only seven days because average temperatures were well above normal.
There is some evidence that this December will not be so gentle.
Expect “a wild ride from start to finish,” the Weather Network said in its Canadian winter forecast released this week. There will be changeable weather patterns featuring extended periods of “high impact weather.”
“High impact weather” is not defined but I translate it to mean rain and freezing rain one week, monster snowfalls the next, then a couple of days of bone shattering cold. A truly genuine mix of miserable winter weather.
Ontario, says The Weather Network, can expect above average snowfall and near normal temperatures.
That forecast follows early predictions by the Canadian Farmer’s Almanac. It predicts much ice, cold and snow for Ontario this winter. Snowfall will be above normal and cold below normal with some places going as low as minus 40 Celsius.
The Almanac says it has 80 to 85 per cent accuracy in its forecasts, except in El Nino years of which 2018 is not one.
Environment Canada, which hedges its bets in statistical gobbledygook and scientific language, appears to be forecasting colder than average temperatures and above average snowfall.
Generally, this year’s winter forecasts have been hedged and as varied as a potluck dinner menu. The reason is that forecasters are uncertain how water temperatures on the Great Lakes will affect Ontario’s winter.
Lake Huron temperatures were below average during an unusually wet and cool summer. That changed quickly, however, with a sunny, warm autumn. Lake Huron’s surface temperature was close to 22 Celsius in late October and has remained above normal.
Warm surface water on Lake Huron can bring lake-effect snow to Muskoka and Haliburton. Cold, dry air picks up heat and moisture when it passes over the warm lake surface, creating bands of lake-effect snow.
The warmer the water and the colder the air, the more intense the lake-effect snow bands become.
December is an ideal month for lake-effect snowstorms because the lake surface is still warm relative to the colder air passing over them. Extremely cold weather freezes the water, obscuring the moisture and heat and making it difficult for lake-effect snow to develop.
Lake-effect snow bands are long and narrow, averaging six kilometres in width and stretching 50 to 400 kilometres in length.
Wind speed often determines how far a lake-effect snow band stretches. Weak winds usually see the snow falling along Lake Huron’s shorelines and into western Muskoka. Strong winds can bring it into Haliburton County.The good news is that when winds are exceptionally strong they pass over the lake’s surface too quickly for snow bands to form.
No matter what the weather gives us this December, one thing is certain: Lake-effect snowstorms are going to be an increasing factor in our winter lives.
Annual average ice cover on the Great Lakes has declined 71 per cent in the last 40 years, says the Great Lakes Integrated Sciences and Assessments Centre based in Michigan. Total annual precipitation increased in the Great Lakes region by 11 per cent during the same period.
The centre also says average temperatures in the Great Lakes region have increased two degrees Fahrenheit (1.1°C) since 1900.
For anyone who wants to compare this December’s weather as it moves along, here are some statistical averages:
The average high December for Haliburton County is minus 1.5 Celsius. The average low minus 12.5°C. The record high for December was 14.5°C recorded on Dec. 5, 2001. The record low was minus 38.5 recorded Dec. 27, 1993. The average December snowfall is 59 centimetres.