We had a welcomed extension to summer here in southern Manitoba in September. With an average mean temperature of 15.4°C, September 2013 tied with 1920 for 8th warmest since 1872.
Warm Septembers have become a consistent trend here in Winnipeg. Since 1990, only 7 Septembers (29%) were colder than the 30-year normal and since 2000 there have been only 3 (21%). And they weren't even THAT cold... In fact, you have to go all the way back to 1999 to find the last September that was at least 1.0°C colder than normal. Therefore in brief, we have now gone 14 straight years without a single September that was 1.0°C colder than normal. In that same period, 8 Septembers were at least 1.0°C ABOVE normal.
The following graph shows that Septembers are as warm as they've ever been right now. In the last 10 years (including 2013), the average mean temperature in September was 14.0°C. That's the warmest 10-year average since 1881.
Back to this past September, there were a few highlights:
The heat of September 6 was the biggest event of the month as temperatures soared to 33.8°C, the hottest September day in 30 years. It was also unusually humid with humidex values reaching 40, prompting a very rare September humidex advisory to be issued by Environment Canada. The humidex peaked at 40.4 at the airport which made it the latest occurrence of humidex over 40.0 since humidex records began in 1953. It was also the 4th highest humidex value in September:
Highest humidex values in September since 1953...
1. 45.9 on Sep 2, 1983
2. 41.4 on Sep 5, 1978
3. 41.2 on Sep 2, 1960
4. 40.4 on Sep 6, 2013
5. 39.2 on Sep 10, 1998
A record high minimum of 17.9°C also occurred on that day.
Other than that, the month was fairly pleasant with only brief cool downs here and there. Although the airport reached -1.3°C on the 21st, most parts of Winnipeg have yet to freeze this fall.
It is also important to note that although 34.5 mm of rain fell throughout the month, only 5.0 mm fell in the first 25 days of the month. The higher monthly total was thanks to beneficial rains on the 28th which dumped 20-27 mm of rain over the city.
Thunderstorms were more abundant in September than what we're accustomed to. In total, there were 7 severe thunderstorm days across Manitoba including a fairly late severe thunderstorm event in western Manitoba on the night of September 25-26.