Top ten weather stories for 2007: story four

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4. Tropical Summer on the Prairies

Each summer across the Prairies a couple of weeks of warm, sunny weather is expected and welcomed. But for several weeks this summer, hot, thick, and unusually sticky air tried the patience of many Prairie residents, playing havoc with everything from hospital surgeries to people's hair.

Calgarians suffered through their second hottest July on record, a mark set more than 70 years ago in 1936. Edmonton International Airport recorded its highest average July temperature at 18.4°C, eclipsing the high mark set only last year. It was a scorcher in the Alberta capital. On seven days, the maximum temperature soared above 30°C. Normally, only one day would hit that high in July, if at all. In Regina, it wasn't the hottest July on record, but the warmest most residents could remember. Three hotter Julys occurred in 1886, 1936, and 1937. The big talk was the uncharacteristically high humidity. The controlling weather system - a huge upper ridge situated in the American Midwest - was a little farther east than normal, enough to tap moisture from the Gulf of Mexico and move it into the Prairies. Combined with local sources from transpiring crops and evaporating surfaces soaked by copious spring rains, it filled the air with insufferable humidity. From July 22 to 24, Regina recorded 29 hours of humidex values above 40, including a reading of 48 for two consecutive hours, shattering the previous record of 44.5. Without question, it was the most uncomfortable spell of weather in Regina's history.

If it was sultry in Regina, it was downright oppressive in Carman, Manitoba. On July 25 at 3:00 p.m. CDT, Carman registered the day's maximum temperature at a sizzling 34°C with a dew point of 30° - literally jungle humidities. (It is unconfirmed, but the 30° dew point might be a new record high in Canada.) The combination of excessive heat and humidity generated a humidex rating of 53, breaking the all-time Canadian record of 52.1 set in Windsor, ON on June 20, 1953. On the same day, Winnipeg's humidex reached 48, breaking its all-time record of 46.1 set in 1996.

Unsafe humidity levels forced the cancellation of hundreds of elective surgeries at several hospitals across the west. High humidity compromises sterile equipment and increases the risk of post-operative infection. The elderly found it hard to cope with the high heat-humidity, which often causes nausea and dizziness from exhaustion and dehydration. Horses at Winnipeg's Assiniboia Downs were given time off because of the danger of heat stroke. Stores struggled to keep fans and air conditioners in stock. Finding air conditioning was only half the battle; getting it installed or serviced was a two-week wait. The warm moist air put a strain on utilities and helped establish a new summer record for power consumption, coming close to winter's record peak load. In some spots, bloated fish floated onto the shores of several overheated lakes, streams and reservoirs. "Summer kill" occurs when high temperatures and little or no wind create oxygen depletion, suffocating fish. Hundreds of dead ducks also turned up in lakes east of Calgary, probable victims of a toxin that thrives in hot, dry weather.

The extreme heat and humidity also wreaked havoc on crops, hitting canola and peas the hardest. Scorching temperatures and dry skies reduced grain yields and lowered quality across the West. In some areas, it was a disappointing year with a double weather whammy - a wet spring and torrid heat in summer. Excessive heat and dryness, however, meant fewer crop diseases and pest problems and advanced crop development.

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