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.

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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:

Month	High Temperature	Mean Temperature	Low Temperature
September	22.2°C 9th warmest	15.8°C 6th warmest	9.4°C 4th warmest
October	12.9°C 30th warmest (tie)	7.1°C 30th warmest (tie)	1.3°C 40th warmest (tie)
November	2.8°C 21st warmest (tie)	-0.9°C 16th warmest (tie)	-4.7°C 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.

Mild and Generally Pleasant October

It was generally a pleasant October in southern Manitoba with numerous warmer than normal days and few below normal days in between. Generally warmer than normal conditions are expected to continue this November. As has been the case in many strong El Nino winters, this coming winter has a good chance of being above normal as well.

22 days exceeded 10°C in October, above the normal of 17 days. The warmest conditions coincided with the Thanksgiving long weekend. Temperatures reached the low to high 20's on Saturday the 10th and Sunday the 11th. Although Winnipeg didn't break any records, many parts of southern Manitoba did. The warmest temperatures were seen along the US border where highs near 28°C occurred in Pilot Mound, Morden and Sprague.

Wpg Oct 12, via Jeff Stapleton/CBC

The Thanksgiving weekend wasn't all perfect as a strong low pressure system brought southern Manitoba its stormiest day of the month on Monday the 12th. Vicious winds were the main story with sustained winds of 60 to 80 km/h and gusts of 85 to 100 km/h in the morning and afternoon. Damage occurred, especially to trees and power lines. The system also brought some weak thunderstorms on Sunday evening, including in Winnipeg. This was just over a week later than the 1981-2010 normal last thunderstorm of the year of October 2.

Frequent light rains brought rainfall totals slightly above normal in Winnipeg. Only 35.9 mm fell at the airport but closer to 45 mm fell in South St Vital. Normal is about 33 mm. No snow was officially recorded, only the 16th October since 1872 to not receive a single snowflake. Some snow pellets did fall in some isolated parts of the city mid month however.

Yet Another Summer-Like September

2015 continued the trend of warming Septembers in southern Manitoba. Winnipeg Int'l A averaged 15.8°C, the 6th warmest September on record since 1872. This was also the warmest since 2009 and the second warmest since 1948. The following table lists the top 10 warmest Septembers since 1872:

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)

This September was the 4th consecutive warmer than normal September and the 17th warmer than normal September in the last 22 years. The last time we had a September that was over 1.0°C below normal was in 1999. Since then, 9 Septembers (out of 17) averaged over 1.0°C above normal. The 30-year September average ending this year (1986-2015) rose to 13.3°C, an increase of 0.4°C since the 1981-2010 normal and an increase of 1.0°C since the 1971-2000 normal. This was also the warmest 30-year period for Septembers since 1872.

Henteleff Park on a warm and sunny September evening

The following graph shows how average mean temperature in September has varied since 1872. The top 30 warmest and coldest Septembers are indicated with red and blue dots. Interestingly, we have not had a top 30 coldest September since 1993. Since then, 9 Septembers were in the top 30 warmest. The green line shows the previous 30-year average which gives an idea of how the September normal has changed. It shows a rapid warming in the last decade. This doesn't mean the warming will continue forever because as you can see, the normal goes through up and down periods.

 

Early September Heat Wave Brought Record Humidity

Right off the hop, September greeted us with a heat wave in its first few days as temperatures exceeded 30°C for 3 consecutive days. Some locations exceeded 32°C on these 3 days, reaching official heat wave status. However, the main story was the humidity as record high dewpoints moved into southern Manitoba. In Winnipeg, dewpoint reached 23.1°C on September 3, the second highest dewpoint in September since 1953. This came very close to the all-time September high of 23.4°C on September 2, 1983. The minimum hourly dewpoint observation for the day was 18.7°C, an all-time high minimum dewpoint for September. The previous record was 17.2°C on September 3, 1960 and September 10, 2005. Three other high maximum and high minimum dewpoint records were broken on Sep 4th and 5th.

The heat and humidity combined to bring some of the highest humidex values on record in September. Humidex exceeded 40.0 on both the 2nd and the 3rd. This was the most 40+ humidex days on record in September. In fact, there had only been 4 other occurrences of humidex over 40 in September since 1953. Humidex peaked at 42.0 on September 2, the second highest in September since 1953. The following table lists the only occurrences of humidex over 40 in September since 1953:

Occurrences of humidex over 40 in September since 1953:
1.  45.9  (Sep 2, 1983)
2.  42.0  (Sep 3, 2015)
3.  41.4  (Sep 5, 1978)
4.  41.2  (Sep 2, 1960)
5.  40.4  (Sep 6, 2013)
6.  40.1  (Sep 2, 2015)

Interestingly, half of the occurrences of humidex over 40 in September occured in the last 3 Septembers.

Humid Month Overall

With an average hourly dewpoint observation of 9.8°C, September 2015 was the 3rd most humid since 1953. Three days had dewpoints exceed 20°C, tied with 1970 and 2005 for second most since 1953.

Drenching Thunderstorms September 4-5

Heavy thunderstorms on September 4th and 5th marked the end of the early-month heat wave. The event started in the early morning between 1 and 8 am on September 4. Nocturnal thunderstorms dropped large hail south and east of Winnipeg with dime to toonie-size hail reported from around Niverville to Cooks Creek to Selkirk. Large hail also fell northwest of Minnedosa around Strathclair and Shoal Lake where quarter to loonie-size hail was reported. The hail was enough to cause some minor crop damage according to reports on social media.

Strathclair area Sep 4. By Ricky Memryk

 

 

 

Additional thunderstorms moved up the Red River Valley in the afternoon on September 4, producing strong winds and flooding rains. The Winnipeg area was one of the hardest hit areas as heavy thunderstorms moved in mid afternoon, plunging the city into night-like darkness. Generally 30 to 50 mm of rain fell in less than 1 hour, causing significant street flooding. Wind gusts up to 83 km/h were also recorded at Winnipeg Int'l A. The rain and wind combined caused visibilities to drop below 1 km. Behind the storm, additional heavy rains fell until evening. Daily totals were generally between 40 and 60 mm in Winnipeg. The airport recorded 41.1 mm, breaking the old record of 36.8 mm in 1872 for the day. Similar totals close to 50 mm were also recorded in the southern RRV near Letellier.

Winnipeg Sep 4. By Felicia Wiltshire

Heavy thunderstorms moved up the RRV once again late day on September 5. Generally 15 to 30 mm of rain fell south and east of Winnipeg. Locally higher totals near 40 mm fell near Letellier. Additional rains later in the month brought monthly totals to over 110 mm in the Letellier area.