Weather: A roller-coaster weather year for Ontario

Tuesday, March 2, 2010

Though temperatures and precipitation were near-normal averaged over the year, month by month the weather gave us a wild ride in 2009

by HENRY HENGEVELD

Mark Twain once noted that "if you don't like the weather in New England, just wait a few minutes." Twain would likely have said the same about Ontario last year!

Averaged over the entire year, 2009 was a rather "normal" year across the province. 

Temperatures in the Great Lakes Basin, for example, averaged only 0.1 C above the long-term mean, while total precipitation was 2.6 per cent above normal. Yet, month by month, the weather behaved like a roller coaster, fluctuating from one abnormal state to another, and back again.

The year began with a cold and snowy January. It added significantly to the excessive precipitation of late 2008 still lying on the ground, resulting in a thick blanket of snow spread across the province. Then, in February, a warm blast of air from the south crossed into southern Ontario, bringing with it several days of double-digit temperatures and heavy rains. These conditions quickly denuded much of the region of its snow cover.

With the underlying soil still in a frozen state, the melting snow and rain caused streams and rivers to rise rapidly. Serious flooding resulted in a number of southern Ontario communities. 

Following the February drenching, the weather became very dry. Much of south central Ontario received only traces of snow during the entire month of March. London had no measureable snowfall for 42 consecutive days between late February and early April.

April came in warm – and very wet – particularly in southern and central Ontario.

Hamilton and Toronto, for example, both recorded monthly rainfall about 90 per cent above the norm. Ottawa fared a bit better, with an excess of about 23 per cent. 

Much of the rest of the year followed a similar sequence of anomalies.

May was relatively normal, but June was cool, and July cool and very wet. Temperatures finally returned to near-normal in August, but heavy rains again pounded the south central regions of the province. 

September once again brought drier conditions. In fact, no rain was recorded at the Pearson International Airport from Aug. 31 through Sept. 18, a September dry spell unprecedented since 1938. The dry spell came with 50 per cent more sunshine than usual, and temperatures about three degrees higher than normal.

A routine October was followed by a mild, very dry November and a near-normal December. During this period, regions of south central Ontario outside of the snowbelt areas received unusually little snow. In fact, downtown Toronto had the first snow-free November since record keeping began there more than 160 years ago.

Although the past spring and summer was relatively cool, the warm season also brought some of the deadliest weather on record. During the year, 29 tornadoes hit various parts of the province, more than twice the norm and matching the record set in 2006.

The first two occurred unusually early in the year – on April 25 – hitting Windsor and Ottawa. Fortunately, these were F0, the weakest rating for a tornado, that caused relatively little damage. Others that followed were less forgiving. On June 25, a powerful thunderstorm that spawned an F2 tornado tore through southwestern Ontario. Then, on July 9, another F2 tornado ravaged a fishing camp in northwestern Ontario, claiming the lives of three American fishermen.

On Aug. 20, a complex system of supercell storms and squall lines produced intense winds from Windsor to northeast of Toronto and destructive tornadoes in Vaughan, Newmarket, Simcoe County and the Muskoka and Parry Sound Districts.

In total, the day's weather produced at least 18 tornadoes (a record for the most tornadoes in one day in Canada) – four weak F0 types, 10 in the F1 category and four F2 events. One storm turned deadly, killing an 11-year-old boy. Total property losses were about $100 million. 

Average temperatures for all of Canada were a half degree warmer than normal, while there was two per cent less precipitation than the mean. All regions of the country experienced annual average temperatures that were warmer than or near to normal.

However, as in Ontario, the conditions from month to month were anything but normal. In the North, it was the warmest summer on record, with temperatures nearly two degrees warmer than normal. On the other hand, the Prairies registered the second coldest summer in 16 years. Alberta also experienced a series of powerful and deadly winds, devastating hail storms and prolonged drought.

The summer was very wet in Atlantic Canada, but sunny and dry in usually wet British Columbia. The latter caused high levels of forest fire activity in the West, with costs to fight the wildfires estimated at $400 million. In the North, the thinning and shrinking of the ice, albeit not as remarkable as in the two previous summers, continued to have a profound impact on the region's people, plants and wildlife alike.

However, the wet, cool summer conditions across much of the country also provided much cleaner air than normal, no summer power crises and fewer mosquitoes carrying the West Nile virus.

Globally, according to the World Meteorological Organization, 2009 was another warm year. Surface temperatures averaged 0.44°C above normal, making it the fifth warmest year on record.  While North America was relatively cool, large parts of southern Asia and central Africa appear to have experienced the warmest year on record.

Climate extremes, including devastating floods, severe droughts, snowstorms, heat waves and cold waves, were recorded in many parts of the world. There were 850 destructive natural hazard events recorded globally in 2009, well above the long-term average.

The arrival of an El Niño during the year also influenced hurricane behaviour, with above-normal activity in the eastern Pacific and a relatively quiet season in the Atlantic Ocean and Caribbean Sea.

However, despite the benign North Atlantic hurricane season, international insurance giant Munich Re estimates global economic losses due to the year's weather disasters to be about US$50 billion. While much less than the estimated $200 billion in losses that accumulated in 2008, this is still well above the long term mean. 

And that's the way the weather was in 2009. BF

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