September Brought Mild Temperatures, Wet Weather

September brought mild weather to Winnipeg with above normal temperatures on about two-thirds of the days in the month. The month also started off extremely dry, but a change to a more unsettled pattern mid-way through the month ended up producing measurable rain on 9 of 13 days, including 25 mm of rain on September 22.

September is typically a month that brings a lot of cooling to the region; the daily mean temperature drops from 15.6°C at the start of the month to 9.3°C at the end of the month, a drop of 6.3°C. So while the average daytime high did drop considerably through the month in line with this trend, temperatures still remained generally above normal, with cool spells few and fair between. The warmest day of the month came on September 12, when Winnipeg set a new daily record high temperature of 34.8°C, beating the old record of 33.3°C set in 1952. That day was also the most “warmer than normal” day of the month with a daily mean temperature of 24.3°C, a full 11.3°C warmer than the normal daily mean of 13.0°C.

The coldest temperature of the month came on September 29th, where the temperature dipped to a chilly -1.2°C in the morning, 4.6°C below the normal seasonal low of 3.4°C.

September had a monthly mean temperature of 14.2°C, which was 1.9°C above the seasonal normal of 12.3°C. The mean daily high temperature was 20.1°C, which was 1.6°C above normal. Warmer than normal daily highs occurred on 20 out of 30 days. The mean daily low temperature was 8.2°C, which was 2.2°C above normal. Warmer than normal daily low temperatures occurred on 21 of 30 days.

The monthly temperature range was 36°C; from a maximum temperature of 34.8°C on September 12 to a minimum temperature of -1.2°C on September 29.

The longest stretch of above-seasonal days was 8, from September 7 to September 14. The longest stretch of below-seasonal daily mean temperatures was 3, which occurred on September 4-6, 15-17, and 24-26.

An Abrupt Mid-Month Change Brought Rainy Conditions

September begin with very dry conditions, continuing the trend from August, which saw dramatically lower than normal rainfall. Mid-month, however, a significant shift occurred which brought disturbance after disturbance across southern Manitoba, producing much rainier conditions.

As can be seen above, very little rain fell between September 1 to September 14, with just 1.8 mm over two rainfall events. Beginning September 15, however, came rain on 9 of 13 days, producing the wettest 10-day stretch of 2017. Between September 17-26, 61.5 mm of rain fell in Winnipeg, eclipsing the 60.8 mm of rain that fell between July 15-24. The largest rainfall event occurred on September 22, when 25.2 mm of rain fell. This was followed quickly by another 18.3 mm on September 24. These two events combined to make the highest 3-day rainfall total of 2017 as well at 43.5 mm, beating 32.2 mm between July 11-13 by 11.3 mm.

With a monthly total of 67.1 mm, Winnipeg exceeded the seasonal normal of 45.8 mm by 21.3 mm.

2017 Annual Precipitation Statistics – Updated October 1, 2017

By mid-September, Winnipeg had crept into having the driest year since 1980, however the rainfall through the second half of the month has eliminated that potential by raising our annual precipitation amounts above the driest on record. Winnipeg still remains well below-normal, outside 2 standard deviations from the 1981-2010 normal amounts.

All in all, September was a beautiful month. Exceptional warmth through the first half gave way to near-seasonal temperatures in the second half, but overnight lows that remained well above-normal through much of the month helped keep that fall chill away until near the very end. The rainfall through the second half of the moth helped alleviate some of the drought that the region has seen, although Winnipeg still sits in a significant precipitation deficit for the year.

October has continued September’s trend so far with most of the days bringing above-normal temperatures to the region. Precipitation has been sparse, though, and little is on the horizon. Although Winnipeg saw its first snowfall of the year on October 14, temperatures will rebound well above-normal with unseasonably warm temperatures expected to build into the region later this week. With daytime highs nearly 10°C above normal and mild overnight lows, it looks poised to offer one last stretch of summer-ish weather before jacket weather arrives for good.

August Brought Mild Days, Cool Nights, and Almost No Rain

August was an interesting month regarding temperatures, particularly because the overall trend was shaped largely by the distinct lack of humidity. The monthly mean temperature ended up slightly below seasonal, but that was driven by unseasonably cool overnight lows. In fact, the average overnight low for August 2017 was 2°C below the seasonal average. Contrast that with daytime highs that were actually warmer than normal; August 2017 ended with an average high slightly above the seasonal average.

Perhaps of note, humidity levels were quite low through the month of August. We don’t quite have the dew point climatology set up here at A Weather Moment, so I asked Winnipeg’s resident weather statistician how August 2017 ranked in terms of average dew point:

So August 2017 ended up the 16th least humid of the last 64 years. The reason cooler nights can be linked to the low levels of humidity come from a simple physics lesson many learn in high school: dry air heats up – and conversely cools down – more quickly than water. The drier conditions allowed temperatures to climb high, but also allowed it to cool off more significantly at night.1 As an aside, this is why many humid places have smaller temperature ranges from day to night, while the driest places on earth typically have huge temperature ranges between day and night.

Getting into the actual statistics, August 2017 ended with a mean temperatures of 17.7°C, -0.8°C below the seasonal average of 18.5°C. The average daytime high was 25.5°C, 0.5°C above the seasonal average of 25.0°C. The average overnight low ended up at 9.9°C, -2.0°C below the seasonal average of 11.9°C.

August wraps up Summer 20172, which ended up with a mean temperature of 17.8°C. That places it as the 87th warmest3 on record, and comes in -0.6°C cooler than the summer of 2016.

Rain, What Rain?

Another notable aspect of August 2017 was the distinct lack of rainfall. Typically Winnipeg will receive around 77 mm of rain through August, but this year the city received only 14.1 mm at the airport, a mere 18% of the normal monthly rainfall.

August was just another month in the story of summer 2017: it was dry. The summer season accumulated 136.7 mm of rain at the airport, which was just 56% of the seasonal normal of 244 mm.

2017 Annual Precipitation Statistics – Updated September 20, 2017
Winnipeg is currently experiencing one of the driest years since 1981.

The drier pattern began in May, and then has not relented. While other areas in the Red River Valley are not quite in as dry a spell as Winnipeg, a general trend of dryness has persisted across much of the region.

August 2017 had measurable precipitation on just 6 of 30 days, with the single largest one-day rainfall total of 6.7 mm on Wednesday August 9th.

August 2017 was actually quite a pleasant month in many ways: most days brought a pleasant and dry summer warmth while evenings were cool. The month brought plenty of sunshine with rain being an elusive sight, continuing the dry trend that began in May of this year.

September has been quite a different month so far, with significant warmth in place this month. Winnipeg hit the warmest day of 2017 on September 12th when temperatures climbed to a record-setting high of 34.8°C. Daytime highs and overnight lows have largely been above-normal much of the month. While rain was sparse at the beginning of the month, the latter half has so far shifted into a more unsettled pattern, bringing relatively frequent rainfalls to the region, although Winnipeg has managed to elude much of the activity.

  1. I also asked Julien to calculate the correlation between humidity levels and highs and lows. Daily low temperatures had an r value of 0.61, showing a much stronger correlation than daytime highs which had an r value of 0.28.
  2. Meteorological summer runs through June, July, and August.
  3. …or 59th coldest, depending how you prefer to look at it.

July Finishes Slightly Cool with Near-Normal Rainfall

July 2017 spent much of it’s time with below normal temperatures — 16 of 31 days had daily mean temperatures below the 30-year average — but was still generally pleasant with much fewer days of rain than in June and many daytime highs that were close to seasonal values.

The first third of July consisted of a swing from well below-normal temperatures to well above normal temperatures followed by a brief period of near-normal temperatures. The deviations from normal more-or-less cancelled each other out with a month-to-date departure from normal of -0.2°C by July 10th. For the next 14 days, though, Winnipeg fell into a prolonged period of below normal temperatures with daily means generally 1.5 to 2.5°C below normal. By July 23rd, Winnipeg’s month-to-date departure from normal had fallen to -1.2°C. The end of the month saw an abrupt turnaround, though, as hot and humid weather moved into the region. Several days saw high temperatures in the upper 20’s to low 30’s and overnight lows in the mid- to upper-teens.

No record temperatures were set in July, however.

By the end of the month, the warm spell had allowed the monthly mean temperature departure from normal to recover to -0.4°C.

In other temperature statistics:

  • July 2017’s average high temperature was 25.7°C, just -0.1°C below the 30-year average of 25.8°C.
  • July 2017’s average low was 12.5°C, -0.8°C below the 30-year average of 13.3°C.

Near-Seasonal Rain at the Airport

While there was only rain on 8 of 31 days in July, total rainfall ended up near-normal with 71.1 mm.

While it rained infrequently, the Winnipeg airport measured a total of 71.1 mm of rain through July 2017, 90% of 30-year normal of 79.5 mm. Much of the rain fell on just 3 days: July 11 (21.7 mm), July 21 (14.1 mm), and July 22 (14.3 mm). The combined 3-day total of 50.1 accounted for 70% of the month’s rainfall.

The 8 days of measurable precipitation was a welcome improvement from June which saw 14 days of measurable precipitation. The concentration of the bulk of the rain into just 3 days did make for some drying, though, and some gardeners likely needed to begin watering their plants occasionally again.

It is worth noting, however, that rainfall was variable throughout the city. At my Glenwood personal weather station I measured slightly less at 68.6 mm. Some locations over south and eastern Winnipeg saw as little as 50-55 mm while other locations across the west side of the city saw up to 85 mm.

So in the end, July 2017 was a very nice rebound from June. There were few days with rain, quite a few days with near-seasonal highs and a lack of humidity that brought more frequent slightly below-normal temperatures at night.

August seems to be continuing the trend so far with near-seasonal highs and cooler nights courtesy a lack of humidity. No complaints from this author!

Unless otherwise noted, all normal values referred to in this post use the 1981-2010 normals for Winnipeg, Manitoba.

The Average of the Extremes Made June A Near-Seasonal Month

June 2017 started off with exceptional warmth as daily mean temperatures1 climbed 5-10°C above normal, a sharp break from a cool end to the month of May. Temperatures peaked on June 2nd when two new records were set in Winnipeg:

  • Record daily maximum of 34.5°C, breaking the old record of 32.2°C set on June 2, 1948.
  • Record warm daily minimum of 17.6°C, breaking the old record of 17.5°C set in June 2, 1988.

The warmth continued with above-seasonal temperatures gradually trending towards seasonal values by mid-June.

A significant pattern shift occurred on June 15th, shifting Winnipeg into a prolonged period of below-normal temperatures that would end up lasting the remainder of the month. Temperatures bottomed out on June 24th when Winnipeg set a new record:

  • Record cold daily maximum temperature of 12.6°C, breaking the old record of 13.9°C set in 2004.

Temperatures then moderated to near-normal for the last few days of the month.

From record-setting warmth at the beginning of the month to record-setting cold at the end of the month, June 2017 averaged out to near-normal with a monthly mean temperature of 16.7°C, which was just -0.3°C below the normal monthly mean of 17.0°C. Perhaps a notable example of how the mean can be misleading.

In other temperature statistics:

  • June 2017’s average high temperature was 23.1°C, just -0.2°C below the 30-year average of 19.2°C.
  • June 2017’s average low was 10.2°C, -0.4°C below the 30-year average of 10.7°C.

Perhaps Not As Wet As You Think

Many people think of rain when they think of June, and it certainly had its fair share of precipitation with accumulating rainfall measured on 14 of 30 days, largely clustered between June 9th and 25th where there was measurable rainfall on 12 of 17 days.

While it rained frequently, total rainfall was actually below normal. The Winnipeg airport measured a total of 51.5 mm of rain through June 2017, well below the normal of 90.0 mm. So despite seeing many damp days, Winnipeg ended up with only 57% of the normal rainfall for the month.

So in the end, June 2017 was not quite what it seemed. Despite a mean monthly temperature near-normal, it was actually a month that progressed from record warmth in the first half to record cold in the second half. Despite raining almost half the days of the month, it ended up with just over half of the normal rain accumulation.

June 2017 Temperature Summary – Winnipeg, MB

July is off to a much more consistent start with seasonal to slightly above seasonal temperatures and dry conditions. We’ll be keeping track of how the rest of the month progresses!

With regard to climatological normals in this post, we are using the 1981-2010 Climatological Normals for the Winnipeg International Airport.

  1. The daily mean temperature is the average of the daily maximum temperature and daily minimum temperature.