Friday, 18 December 2015

Warm November Closes 4th Warmest Fall Since 1872

Warm fall weather continued into November across southern Manitoba. With an average mean temperature of -0.9°C in Winnipeg, November tied for 16th warmest since 1872. This was 3.7°C above the 1981-2010 normal.

The bulk of the warmth was in the first half of the month. In fact, Winnipeg saw an incredible 25-consecutive days of above normal temperatures from October 26 to November 19. Five days exceeded 10°C in November, slightly above the normal of three days. No record highs were broken however.

November was also unusually moist. Dewpoints averaged -2.9°C in Winnipeg, the highest on record for November since 1953. This beat the previous record of -3.0°C in 1981. The most impressive dewpoints were on November 16 and 17 when dewpoint temperature reached 9.4°C and 9.3°C respectively. These smashed the old daily records and were the latest occurrences of dewpoint over 9°C on record. Thanks to the humidity, a record high minimum temperature of 5.3°C was also achieved on November 16.

There was also a lack of snow. The first accumulative snowfall of the season was on November 18, a month later than the 1981-2010 normal of October 18. This tied with 1880 for 4th latest first snowfall accumulation (0.2 cm +) of the season.
It was a very warm fall across southern Manitoba. All three months finished in the top 30 warmest on record since 1872. The following table summarizes the average high, mean and low temperatures for each fall month in Winnipeg:

High Temperature
Mean Temperature
Low Temperature
9th warmest
6th warmest
4th warmest
30th warmest (tie)
30th warmest (tie)
40th warmest (tie)
21st warmest (tie)
16th warmest (tie)
16th warmest

The fall as a whole finished 4th warmest since 1872, averaging 7.3°C. Brandon also had a 4th warmest fall on record (since 1890), averaging 6.2°C.

Top 10 warmest falls (Sep-Oct-Nov) in Winnipeg since 1872 (by average mean temperature):
1.  8.6°C (1963)
2.  7.9°C (1931)
3.  7.5°C (1923)
4.  7.3°C (1953, 2009, 2015)
7.  7.2°C (1948)
8.  7.1°C (1914, 1920)
10. 7.0°C (1922)

It was a moist fall as well. Dewpoints averaged 3.2°C in Winnipeg, second only to 2009 when dewpoints averaged 3.6°C. September was the 3rd most humid on record and November the most humid on record.

Summer-like September

 With an average temperature of 15.8°C, it was the 6th warmest on record since 1872 in Winnipeg. It was also the warmest since 2009 and the 2nd warmest since 1948.

Top 10 warmest Septembers in Winnipeg since 1872 (by average mean temperature)
1.  17.7°C  (2009)
2.  16.8°C  (1948)
3.  16.6°C  (1940)
4.  16.3°C  (1897)
5.  16.1°C  (1906)
6.  15.8°C  (2015)
7.  15.6°C  (1931, 1967)
9.  15.4°C  (1920, 2013)

The month started with a 3-day heat wave as temperatures soared into the low 30's. High humidity was the main story with humidex values reaching 42.0 on September 3 and 40.1 on September 2. The humidex of 42.0 was the second highest on record for September since 1953. Prior to this year, humidex values above 40 had been achieved only 4 other times in September. Dewpoint temperature peaked at 23.1°C on September 3 as well, the second highest on record for September since 1953.

The early September heat ended with the last widespread thunderstorm events of the year on September 4 and 5. Nocturnal storms early on September 4 dropped nickel to toonie-size hail south and east of Winnipeg and near Strathclair and Shoal Lake in southwestern Manitoba. Drenching thunderstorms moved up the Red River Valley and southeastern Manitoba in the afternoon. Winnipeg was hard hit with 30-50 mm of rain in less than an hour alongside wind gusts over 80 km/h. 41.1 mm of rain fell throughout the day at the airport, breaking the old record of 36.8 mm in 1872 for the day. Additional drenching thunderstorms moved through in the evening the following day. 15-30 mm fell south and east of Winnipeg with close to 40 mm near Letellier.

Warm Thanksgiving Weekend With a Windy Finish

The warmest temperatures of October coincided with the Thanksgiving weekend. Temperatures soared into the 20's on the Saturday and Sunday. Many parts of southern Manitoba broke records, but not Winnipeg. The warmest temperatures were along the US border with highs near 28°C in Pilot Mound, Sprague and Morden. The weekend did not finish perfectly however. A strong long pressure system brought the stormiest day of the month on Thanksgiving Monday with winds the main story. Sustained winds were between 60 and 80 km/h and gusts between 80 and 100 km/h. Damage occurred, especially to trees and power lines. The system brought the seasons final thunderstorms in Winnipeg on Sunday the 11th. This put this year's thunderstorm season at Winnipeg airport at 127 days long (June 7 to Oct 11), tied for 11th shortest season since 1953.

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