Monday, 4 January 2016

#7, #6 & #5 - Top 10 Weather Stories of 2015 in the Winnipeg Area

#7 - Sizzling in September... Again

A three-day heat wave started September in southern Manitoba. Temperatures exceeded 30°C and in some cases the 32°C required for heat wave status. No record highs occurred in Winnipeg but a record high minimum of 21.0°C was achieved on September 3. This was also the second highest daily minimum temperature on record in September since 1872.

The main story during the heat wave was the humidity as dewpoints rose to record highs. Two high dewpoint records and three high minimum dewpoint records were broken. Dewpoint reached 23.1°C on September 3, the second highest dewpoint on record in September since 1953. This was just shy of the all-time September high dewpoint of 23.4°C on September 2, 1983. A record dewpoint of 22.9°C was also achieved on September 4, the third highest dewpoint in September. In addition to these records, an all-time September high minimum dewpoint was acheived on September 3, with a minimum dewpoint observation of 18.7°C. The previous all-time September high was 17.2°C in 1960 and 2005. The high heat and humidity pushed humidex values to 40.1 on September 2 and 42.0 on September 3. The humidex of 42.0 was the second highest in September since 1953. These were two of only six 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)
Winnipeg September 4, by Felicia Wiltshire
The heat wave ended with a bang as strong thunderstorms hit on September 4 and 5. Severe nocturnal thunderstorms between 1 and 8 am on September 4 dropped dime to toonie size hail south and east of Winnipeg and northwest of Minnedosa. Minor crop damage was reported near Strathclair. Strong thunderstorms moved up the Red River Valley in the afternoon, dumping flooding rains and producing strong wind gusts. The Winnipeg area was one of the hardest hit areas with 30 to 50 mm of rain in just under an hour and wind gusts over 80 km/h. Significant street flooding occurred as a result. With more rain later in the day, daily totals sat between 40 and 60 mm. The airport recorded 41.1 mm for the day, breaking the old record of 36.8 mm in 1872. Heavy thunderstorms moved up the Red River Valley again the following day. 15-30 mm fell southeast of Winnipeg with locally close to 40 mm near Letellier.

Another hot day occurred on September 13. Temperatures exceeded 30°C across southern Manitoba. Winnipeg reached 31.6°C, just shy of the old record of 31.7°C in 1927. The hottest temperatures were along the US border with highs between 32 and 34°C. Numerous records were broken including in Morden and Pilot Mound where highs of 33.8°C and 33.3°C occurred. Generally warm conditions continued throughout the remainder of September with numerous days over 20°C and 25°C. In total, 5 days exceeded 29°C in Winnipeg, tied with three other years for second most in September since 1872.

Overall, it was the 6th warmest September on record since 1872 in Winnipeg with an average mean temperature of 15.8°C. It was the warmest September since 2009 and the second warmest since 1949. Dewpoint temperatures averaged 9.8°C, the 3rd most humid September since 1953. 3 days saw dewpoints over 20°C, tied with 1970 and 2005 for second most in September.

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)

#6 - An Active Manitoba Thunderstorm Season Despite a Late Start

It was a late start to the thunderstorm season across southern Manitoba. The first severe thunderstorm event didn't occur until June 1. In Winnipeg, the first thunderstorm recorded at the airport was on June 7, the third latest start to the thunderstorm season since 1953.

Top 5 latest starts to the thunderstorm season at Winnipeg airport since 1953:
1. June 28 (1958)
2. June 10 (2013)
3. June 7 (2015)
4. June 3 (1992 and 1995)

However, the late start was not forewarning a tame thunderstorm season. Once things got going, they really got going. In the end, Manitoba had the greatest number of reported tornadoes and waterspouts in Canada for 2015. In addition, Manitoba had the most severe hail and severe thunderstorm rain events of the three Prairie provinces. This year was different from the last 4 years in that Winnipeg and the Red River Valley as a whole finally got in on the action.

At least 11 tornadoes and waterspouts occurred in Manitoba in 2015, the most in more than 5 years and the most in Canada for the year. Two events this year brought worldwide attention: at least 2 tornadoes and waterspouts on July 18 near Matlock and at least 3 tornadoes on July 27 in southwestern Manitoba (according to Justin Hobson's chase story).

On July 18, a landspout tornado near Matlock travelled over Lake Winnipeg, becoming a waterspout. The storm then produced at least one other waterspout. The two waterspouts occurred simultaneously, as seen in the photo below by Wray Pearce. The storm and waterspouts were very photogenic and photos spread around the world on social media.
Twin Water Spouts over Lake Winnipeg at Matlock
Two waterspouts over south basin of Lake Wpg July 18; by Wray Pearce
On July 27, a supercell thunderstorm travelled over 100 km from Tilston to northeast of Virden, producing multiple tornadoes in a 3-hour timeframe. Some were quite violent as seen on storm chasers' videos. One tornado reached close to a kilometre wide. Luckily, the strong tornadoes dodged all major communities and narrowly missed Virden. Only a few farms experienced some damage. Environment Canada sent a damage survey team to investigate. The worst damage they saw was from a high-end EF-2 tornado (winds close to 200 km/h). It is entirely possible that the tornadoes may have been even stronger, but when/if they were they weren't hitting anything significant. Photos and video of the tornadoes can be seen by following this link.

Hail was also a big story this summer across southern Manitoba. Almost half of severe hail reports were in August thanks to extreme nocturnal thunderstorm activity mid and late month. Significant hail events occurred on August 12, 22 and 28 and are described later. The following table summarizes the number of reports by category received to Environment Canada in the 3 Prairie provinces from May to September. Notice that Manitoba had the most severe hail and severe thunderstorm rain reports. Also note that number of reports is not equivalent to number of events.

Table: Number of thunderstorm-related reports by category and by Prairie province from May to September 2015

On August 12, severe nocturnal thunderstorms impacted the Onanole area near Riding Mountain Nat'l Park around 7 am. Hail up to golf ball-size damaged vehicles and damaging winds knocked over dozens of trees. The wind also tore part of a home's roof and blew it 300 metres away. Residents in the area thought they had witnessed a tornado, but given the situation it is more likely that it was a microburst. Storms then moved into the Neepawa and Gladstone areas between 8 and 11 am, dropping quarter to golf ball-size hail which damaged crops and vehicles. Widespread thunderstorms continued their trek southeastward throughout the afternoon, dropping loonie-size hail near Plum Coulee and loonie to golf-ball size hail around Vita and Caliento.

Altona Aug 28, by Colleen Otto Harder
The August 22 event will be described in detail later on in the top 10 events series. On August 28, damaging nocturnal hailers occurred southwest of Winnipeg. Toonie-size hail and larger fell from Austin to St. Claude to Roseisle to Plum Coulee to Altona. The Plum Coulee to Altona region was hardest hit with hail up to baseball-size. Major damage occurred in Altona with broken windshields and siding, flattened and shredded plants/trees, damaged crops and dented vehicles. The storm also dumped about 26 mm of rain, causing some street flooding.

Significant hail, wind and flooding rain events also occurred on June 27, July 4 and July 15. Details on these events can be retrieved in the summer summary that was posted here.

#5 - A Very Early Spring

March 13 in Winnipeg. Source: CBC
Similar to 2010 and 2012, spring began much earlier than usual in 2015. April-like temperatures and snow pack melt arrived by the second week of March. The winter snow pack dissapeared in Winnipeg by March 15, tying with 1995 for third earliest snow melt since 1955. This was just a day later than in 2012 and a day earlier than in 2010. It was also a drastic change from 2013 and 2014 when the snow did not melt until April 28 and April 21 respectively. The 1981-2010 normal is April 3.

Record warmth arrived on March 14 and 15 with temperatures reaching the teens. Winnipeg reached 13.2°C on March 14, breaking the old record of 11.4°C in 1981. A high of 14.3°C was achieved the following day, just 0.1°C off the old record of 14.4°C in 2012. The warmest temperatures occurred along the US border with highs reaching the high teens in some cases. Morden reached highs of 18.3°C and 17.6°C, the earliest occurrences of temperature over 16°C on record since 1904. The high of 18.3°C on March 14 broke the old 2012 record by an impressive 7.1°C! Nights were unusually mild as well. A morning low of 6.7⁰C in Winnipeg on March 15 was the warmest morning low for so early in the year since 1953. Previously, the earliest we had a morning low as warm or warmer than that was on March 19, 2012 with a morning low of 16.0°C.

Temperatures after the 15th were no longer record breaking but remained above normal. In the end, March averaged -3.0°C, 2.8°C warmer than the 1981-2010 normal and the 20th warmest March since 1872. Even thunderstorms occurred on March 30 west and north of Winnipeg. Some small hail fell. No thunder could be heard in Winnipeg but some small hail was reported in the south end when some convective showers rolled through.

Warm conditions did continue in April before tapering off in May. The spring as a whole (March to May) tied 22nd warmest with an average mean temperature of 4.5°C.

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