Weather: A winter that beat all records

Thursday, June 10, 2010

Not only was it the warmest since national record-keeping began, it also set a new record for low precipitation levels. The downside is that soils may dry out early and we may be in for a warm summer

by HENRY HENGEVELD

This past winter was, once again, quite an unusual one, at least across Canada. One aspect that made it so was the "heat." From the U.S. border to the high Arctic, and from the Pacific to the Atlantic shorelines, most of the country experienced temperatures well above normal.

Some regions, such as the eastern Arctic and northern Quebec, basked in average temperatures over the December to February period that were more than 6 C above the norm. The only region that was somewhat "cool" was southern Saskatchewan, where temperatures hovered at about 1 C below normal. Averaged across the country, the winter months ended up being 4 C above normal, a new record that edged out the winter of 2005-2006 as the warmest ever since national scale record-keeping began in 1948.

The warm Canadian winter was in sharp contrast to that south of the border. While the American northwest and northeast enjoyed well above average temperatures similar to those in Canada, most of the rest of the U.S. landscape shivered in well below normal temperatures. In the deep U.S. south, from Texas across to Florida, it was one of the coldest winters on record, much to the disappointment of Canadian "snowbirds" vacationing there.

However, our winter wasn't just unusually warm. It also set a new record for low precipitation levels. While the central Arctic and northern Quebec had above-average snowfall, much of the rest of the country received less than 80 per cent of normal precipitation levels. Some areas, including parts of Ontario and the Prairies, had less than 40 per cent of the expected snowfall.  Again, this was in sharp contrast to most of the United States, where precipitation amounts were well above. 

Although El Nino was a major contributing factor to this year's warm, dry winter in Canada (and cool, wet U.S. conditions), the relatively high temperatures are consistent with a long-term trend towards increasingly warmer winters. Over the past 63 years, average Canadian winter temperatures have risen by about 2.5 C.  

Winter anomalies in Ontario were broadly similar to that of the national average.

Northern Ontario had its warmest winter ever (4.2 C above the norm) and received 25 per cent less precipitation than expected. The Great Lakes Basin experienced a more moderate warm anomaly of 2.1 C, but an average precipitation amount almost 29 per cent below normal.

The seasonal departures from normal were dominated by large anomalies during January and February. For example, during those months, Sudbury temperatures averaged more than 7 C above average, while Ottawa's were about 6.6 C above. Those in southern parts of the province were between 3.5 and 5 C above normal. 

The weather patterns established during the winter season continued into March. In Ontario farmland and cottage country, temperatures during the month averaged between 2.5 and 8 C above the norm. Many locations had no snowfall and very little rainfall. Only the Toronto-Hamilton region, at the west end of Lake Ontario, received above normal precipitation.  

Seasonal forecasts issued by Environment Canada in early April projected that warm, dry conditions would, on average, continue throughout most of Canada during the April to June period. 

Other than the cross-country skiers and snowmobilers, most Ontarians appeared to enjoy the mild, dry winter with hardly any snow to shovel, much safer roads and low home heating bills. Frogs were already happily chirping in their ponds by late March. With the relatively dry soil conditions and warm temperatures through most regions by early April, an early crop planting season seemed likely.

However, there is always a downside to unusual weather behaviour. Our Ontario ecosystems depend on the runoff from spring snow melt and an adequate supply of spring showers to replenish and maintain soil moisture and water levels in streams and ponds. With virtually no snow on the ground in most Ontario farmlands by the onset of the spring melt season, there was no spring freshet this year. Furthermore, if projections for a warm, dry spring season hold true, soils will dry out early. 

That's not good news for farmers and the natural resources sector. Dry soils imply increased risk of crop failures due to moisture stress, and of large loss of forests due to wildfire. Low stream and pond levels also threaten the adequacy of water resources for irrigation and reduce the quality of the water.

Warm, dry air is also usually associated with a greater number of days with extreme heat, and often results in frequent occurrences of poor air quality days in highly industrialized regions such as the lower Great Lakes. Furthermore, low lake and river levels can severely affect marine transportation on the Great Lakes and reduce the efficiency of hydro-electrical power stations. 

Let's hope that, this time, the seasonal forecast for a hot, dry spring in Ontario
is wrong. If not, this could be a rough summer! BF

Henry Hengeveld is Emeritus Associate, Science Assessment and Integration Branch/ACSD/MSC, Environment Canada.