Top ten weather stories for 2010: story nine
9. Freak Canada-U.S. "Weather Bomb"
For three days during the last week of October, a massive and powerful fall storm muscled its way across North America from the Dakotas to the Great Lakes and beyond. The unusual system fascinated meteorologists because its strength was similar to a Category 3 hurricane. Weather advisories were issued for 31 states and six provinces for a buffet of severe weather: tornadoes, blustery blizzards, powerful gales, wind-driven rains, heavy snows and thunderstorms. Lumped together, the ugly mix was called a “weather bomb” because of a central pressure drop of 28 millibars in 24 hours, which is a hallmark of this type of storm. Most “bombings” in North America occur over water, commonly along the U.S. Eastern seaboard and in Atlantic Canada, while land bombs are rare. Yet this was one of the most intense storms ever to form over mid-continent – second to the Great Ohio Blizzard in January 1978, but more powerful than both the storm that sank the Edmund Fitzgerald freighter on Lake Superior in November 1975 and the March 1993 “Storm of the Century”.
The fall storm blew in from the Pacific Northwest on the strength of a jet stream that was about one-third stronger than normal for this time of year. As the system moved eastward, it drew in warm, moist air from the American south that collided with the season’s first cold air from the North creating a supercharged storm that exploded over Minnesota. In Canada, the storm generated blizzards in the West with 20 to 30 cm of snow near the Saskatchewan-Manitoba border, storm surges on Manitoba lakes, and heavy rains and strong winds in Ontario and Quebec. Additionally, parts of southwestern Ontario near Windsor and Sarnia came under a tornado watch. And many roads in the eastern Prairies became ice covered and slippery from the snow that first melted on warm highway surfaces, only to freeze into black ice under a thin cover of blown snow.
Across North America, the storm snapped trees and power lines, closed highways, ripped away roofs and delayed flights. But it was in Manitoba where the storm had its greatest impact. Old-timers said it was the worst they'd seen in about 60 years. As a mark of the storm’s intensity, Winnipeg set an all-time record for its lowest-ever barometric pressure. Total storm rainfall in the province ranged from 50 to 100 mm, along with some big snows. The Manitoba lakes, already at record-high levels, rose more than a metre under the wind and pressure stress. Northerly winds blew down the lake for more than 100 km, piling water on the south shore. The set-up forced the overnight evacuation of several low-lying areas where access roads flooded. Huge waves chewed up sand dunes and scoured the fragile shoreline for hundreds of kilometres and up 10 m from shore in some places. Waves crashed over 40-year old earth dikes and rock breakwaters, landing in the yards of lakefront homes and cottages and leaving debris, uprooted trees and dead fish, as waters retreated. Rocks were tossed on shore as frantic volunteers trenched and sandbagged. States of emergency were declared in several communities. In Gimli, 100 km/h winds generated two-metre waves that pushed waters up and over cottages, and washed out roads. At the Sagkeeng First Nation, wind-driven waters came crashing through windows. On Lake Winnipegosis, winds of 110 km/h pushed the Mossey River backwards and forced the evacuation of several residents. The boardwalk at popular Grand Beach Provincial Park was damaged and will have to be rebuilt in places. Officials worry that the “weather bomb” might set the stage for one of the most destructive and disastrous spring floods on record given that several Manitoba lakes and rivers are near their highest levels ever. Normal or above-normal snowpack combined with a quick thaw could only worsen a bad situation.
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