Weather: Canada's weather warning system found wanting

Wednesday, November 4, 2009

The Aug. 20 tornadoes that struck south-central Ontario were a reminder of the weaknesses in our weather warning system and the need for more resources within the atrophied budget of the Canadian weather service

by HENRY HENGEVELD

Severe thunderstorms are a normal part of Ontario summer weather. They usually bring strong winds, intense rainfall, and lots of lightning and thunder. In the middle of such a storm, it can get scary at times, but it's also fascinating to watch!

Every once in a while – thankfully, not very often – these storms also generate tornadoes. This summer, Thursday, Aug. 20, was one of those times. 

The day before, Environment Canada forecasters in the Toronto weather office began monitoring a band of severe thunderstorms making its way through the U.S. Midwest, ahead of a cold front. By early Thursday morning, it became apparent that the severe weather was indeed headed for Ontario, and that intense thunderstorms were likely to develop across the southern parts of the province. Forecasters included that advisory in their forecast for the day. 

By 6 a.m., there were also concerns among the forecasters that the hot humid conditions and the atmospheric instability ahead of the cold front might have the potential to spawn tornadoes.  However, there was still insufficient evidence to predict their likelihood or where they might occur. 

Shortly after noon on the 20th, the first real evidence of tornado potential began to show up on the Doppler radar. A squall line of intense storms began to develop over lower Lake Michigan, heading for Ontario. At the west end of this squall line, a very intense convective activity, referred to as a supercell, began to form just south of Lake Huron.

At 3:35 p.m., forecasters issued their first tornado warning. By 3:40, the Doppler radar systems indicated the development of circular motions within the Lake Huron supercell consistent with the early stages of a twister.

Within 15 minutes, forecasters released a warning update that alerted residents in its path, including those in Grey County, Markdale and Blue Mountain regions, that severe thunderstorms with tornadoes were imminent. They urged residents in the region to take immediate safety precautions.

The weather office also issued a severe thunderstorm alert for most of the rest of south-central Ontario, adding that these might be accompanied by large hail and damaging winds. By late afternoon, Environment Canada had issued a tornado warning extending the full 500 kilometres between Peterborough and Windsor.

The first tornado struck near the town of Durham shortly after 4 p.m.

By early evening, as the system progressed across the province, a total of nine tornadoes had touched down. They appeared to follow two broad tracks – a northern one that passed over Durham, Markdale, Collingwood and Lake Nipissing, and a more southerly line passing over Milton, Vaughn and Newmarket. Three of the tornadoes were F2 category (winds between 180 and 250 kilometres per hour).

While insurance companies indicated it would be months before all the claims were processed, estimates for damages in the Collingwood area alone exceeded $20 million. In the Vaughn region, some 600 homes, a school and numerous business establishments were seriously damaged, with about 40 of the damaged homes declared uninhabitable. Some 2,500 people were required to vacate their homes. Thankfully, while the Durham tornado tragically killed a young camper, and one of the victims in Vaughn died of a related heart attack, there were no other serious direct injuries.

Elsewhere, the severe thunderstorms that passed through not only brought awesome displays of thunder and lightning, but also dumped 30 millimetres of rain in some areas, pea-sized hail in others, and winds that snapped trees and caused power outages for thousands. 

These numbers pale in comparison to the 12 F2 tornadoes that occurred in the Orangeville-Barrie area in May 1985, an event I remember well. (That weekend, I was on a camping expedition with a church cadet group east of Orangeville, three kilometres south of where one of those tornadoes passed by). The 1985 event included two killer F4 tornadoes, flattened a sub-division of Barrie, and caused 12 fatalities.

However, as the worst outbreak of tornadoes in Ontario in more than 20 years, this year's event was a reminder that tornadoes do happen in Ontario, and that there is a need to better anticipate and be prepared for such disasters. They also remind us of the awesome power of weather systems – and of our own powerlessness in predicting these events with accuracy or in preventing the devastation they cause.  

Thanks to Doppler radars, lightning detection systems and supercomputers now in place, the half-hour advance warning of imminent tornadoes on Aug. 20 was as good as they get – even in the Kansas tornado belt.

However, the Canadian infrastructure for ensuring that such warnings reach people is much less effective than south of the border. The U.S. weather service has an Early Alert System in place that flashes immediate warnings to radio and TV stations, mobile devices such as pagers and cell phones, and other broadcast media. Indications are that participation of U.S. broadcasters in passing on the warnings is high, and that the American public often gets precise weather data within minutes.

No such national system exists for Canada. The federal environment commissioner recently criticized Environment Canada for the lack of a national program to verify the timeliness, accuracy or effectiveness of its weather warnings.  Canada's Senate Public Safety Committee also repeated a recommendation for a public warning system for Canada that would include the requirement to have the full participation of broadcasters.

Within days after the event, politicians once again quickly jumped in on the issue of weather warnings and improved disaster preparedness. While viewing the aftermath of the tornado in Vaughn, Ontario Premier Dalton McGuinty indicated it was time for authorities to assess the adequacy of such warnings and act to address deficiencies. His brother, David, environment critic for the federal Liberals in Ottawa, also pointed out that one step in the process would be replenishment of related resources within the atrophied budget of the Canadian weather service.  Anyone listening? BF

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