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Ontario Weather Review - September 2007

September 2007 finished on a high note this year... high temperatures, that is - in fact, record-breaking ones.

Normally, the end of the month is its coolest part, but this year daytime high temperatures were smashed province wide. Not only were daily highs surpassed by two to five degrees on September 25, but this also established the all-time record warm spell for this time of the year. There are rare occurrences of 30 degrees in October, but values of 31 to 34 degrees have never been reported so late in the year.

Overall, the continuing trends of warm temperatures this past summer are also still continuing into fall. The monthly mean temperatures were above normal - in a number of cases, climbing two to three degrees above normal.

The dry to drought-like conditions in Southern Ontario also persisted. Monthly rainfall amounts of 20 to 30 millimetres were reported in many locations, resulting in only a third - or even a quarter - of what is expected for this time of the year.

Ironically, Northern Ontario's precipitation situation was very different. Rainfall values of 40 to 90 millimetres above normal were reported in a number of locations across the north and Kapuskasing shattered a 24-year-old monthly record for most rainfall.

Severe Weather

September was a tale of two vastly different weather regimes. Southern Ontario enjoyed long periods under the influence of high pressure, which provided plenty of sunshine and above-normal temperatures. However, this same area of high pressure deflected a parade of low-pressure systems that rolled over Northern Ontario, bringing clouds and rain. On a few days during the month, places like Geraldton, Wawa, Kapuskasing and Moosonee saw soaking rains with embedded heavier showers and thunderstorms that generated single-day rainfall accumulations in excess of 35 millimetres. In one two-day stretch, Kapuskasing received more than 110 millimetres of rain, with 49.4 millimetres falling on September 6 followed by a drenching 61.4 millimetres the next day.

With respect to significant thunderstorms, there were a couple of active days. The afternoon of September 11 saw thunderstorm activity over regions to the east of Lake Superior, with one of these storm cells producing a probable brief tornado in the Batchawana Bay area to the north of Sault Ste Marie. Fortunately, only minor damage occurred what with peak wind speeds likely around 90 kilometres per hour, making this a Fujita Scale Zero event - the weakest type of storm on the Fujita wind damage scale. By that evening, strong thunderstorms had moved into Southern Ontario, bringing driving rain and gusty winds to a number of communities. There was also a possible funnel cloud sighting to the southwest of Cambridge and a number of trees were knocked over or lost large branches in the community of Galt, south of Cambridge.

The passage of a cold front during the afternoon and evening hours of September 14 also brought some locally heavy rain and gusty winds associated with thunderstorm activity. Some minor damage was reported in the Orleans area to the east of Ottawa around 9 p.m., which coincided with a report of a wind gust to 65 kilometres per hour at the Ottawa airport.

Unusual mean temperature readings:

Record precipitation readings (in millimetres):

Unusual precipitation readings (in millimetres):

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