Tuesday, 3 January 2012

Top 10 Weather Events of 2011 - #6

#6 September heat wave
     A major upper-level ridge built over western Canada during the second week of September. This meant the return of mid-summer heat to southern Manitoba, but also an extension to the summer-long drought. Temperatures from September 6 to 11 were 7 to 12 C above the average of 20 C. September 7 to 10 featured the peak of the heat with highs over 30 C for 4 consecutive days, tying 1940 and 1948 for longest 30 C streak on record for the month. In addition, only 10 Septembers since 1872 have had 4 or more days of 30 C through the month. Although, not one single temperature record was broken this September, since records were still generally in the mid thirties.
     Although it was not officially a heat wave in Winnipeg, it was in other parts of Manitoba. A heat wave is described as having at least 3 consecutive days of 32 C or hotter. Here are some highs from selected cities in Manitoba:

Sept 7
Sept 8
Sept 9
Sept 10
Visible Satellite: So clear, only
contrails were visible.
     Very impressive for September. The strong ridge ensured that all systems stayed very far from the Prairies. Skies were incredibly clear. The only clouds visible on visible satellite were contrails from airplanes. The extensiveness of these crystal clear skies was intriguing.
     Farther west in Saskatchewan, the heat was even lengthier. In Moose Jaw, it was 30 C for 7 consecutive days, bringing a total of 10 days above 30 C for the month of September!
     A week later, temperatures plunged across the Prairies. In Manitoba, sub-zero overnight lows brought the first killing frost for many. Inside urban centres such as Winnipeg and Steinbach, temperatures remained above zero, with only frost on roofs in general.
     Lake waters of 18 C, and winds from the NNW allowed for lake-effect streamers to form, the first lake-effect event of the season. Locally, it was cool enough for ice pellets and wet flurries. 15-25 mm of rain fell in the heaviest bands. In the Winnipeg area, it was cool enough for some hail on the 14th thanks to some scattered showers. It was quite a shock considering we were basking in summer weather just a few days earlier.
     A quick rebound back to the low to mid twenties later in the month ensured that this September would be well above normal. The average monthly mean of 14.2 C was almost 2 C above average, and tied with 1994 and 1997 for 20th warmest September on record.
September 25, still very green - temperatures in twenties

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