Temperature
However, the steady yearly average hides some major trends we have been seeing in certain months of the year. Late winter and spring have seen a dramatic cool down over the past decade, particularly in February and April which have cooled by 0.7°C. For April, this represents the fastest cool down we have ever seen since records began in the 1870s. The cool down during the February to May period is largely the result of losing the 1980s, which featured very mild springs and Februarys. For April specifically, we also entered a sudden cool period starting in 2013, with several Aprils afterward being much colder than normal. The loss of warm Aprils in the 1980s combined with the sudden cool period resulted in the unprecedentedly fast cool down for Aprils.
In contrast to the first half of the year, the second half of the year has been warming up. Fall and early winter have warmed the most. September has warmed by 0.4°C and December by a remarkable 0.8°C. For both of these months, the significant warming was both due to losing the colder 1980s and adding the warmer 2010s. Also of note, average highs in November reached above freezing for the first time in 90 years. In addition, December is now warmer than February which is actually more typical historically.
Despite an unchanged yearly mean temperature, the 2010s were still very warm. The 2011-2020 period averaged 3.1°C while the 1981-1990 period averaged 3.2°C. Record high temperatures outnumbered record low temperatures 3.7 to 1 from 2011 to 2020, not unprecedented because this ratio was 3.8 to 1 in the 1981-1990 period. Only 9 record lows were broken, tied with the 1951-1960 period for the fewest.
Precipitation
Overall, Winnipeg's 1991-2020 normals are snowier and less rainy. The increase in snowfall is primarily due to the loss of the 1980s which were the least snowy decade on record. They averaged 96 cm per year, which was at least 20 cm lower than any other decade. As a result, we have now returned into the normal range of average snowfall historically - between 120 and 135 cm. A slight portion of the increase might also be attributable to the new measurement site in Charleswood, which I use from 2003 to present due to the loss of measurements at the Airport. The sheltering might have a slight increase on snowfall amounts. However, from my research this increase should be very small and potentially negligible. There is overlap between Charleswood and the Airport snowfall reports between 1998 and 2002 and during these years, the snowfall amounts were fairly similar between the two. The bigger difference between the two was with snow on ground measurements. Blowing snow tends to result in lesser snow depth at the Airport, while the sheltering of the Charleswood site results in new snowfall simply accumulating throughout the winter with limited blowing snow to remove it.
Of particular note, September now averages 0.0 cm of snow. This is the first time in Winnipeg's history that this has occurred and is the first time that 4 calendar months average 0.0 cm of snow. This is not to say that it can't still snow in September, because it did as recently as 2018. But actual accumulations have been very small to non-existent. It is likely that the reduction in snow is due to the warming we have seen in September, and it cannot be guaranteed that the 0.0 cm average will sustain itself long-term as a result.
Due to the dry cycle we have been in for the past decade, rainfall has decreased significantly in the summer months. June has experienced the greatest loss, with 12.6 mm less rainfall on average. In fact, June, July and August now all average about the same amount of rain. July is now the second wettest month of the year for the first time in 40 years, though this is not unusual historically as seen in the following graph.
An increase in rainfall in September was primarily due to the the wet Septembers of 2018 and 2019. September was actually on track to average less precipitation until these Septembers occurred. An increase in rainfall in May is due to the loss of the extremely dry 1980s. May was also very wet from the mid 1990s to the mid 2010s, before drier Mays returned in last few years of the 2010s.
Due to changes in instrumentation at the Airport and measurement methods, precipitation amounts are more difficult to analyze nowadays. I will not include much details about it in this post as a result. I believe it is more interesting and revealing to look at rainfall and snowfall specifically, rather than precipitation as a whole.
Thunderstorms
Related to the dry cycle we have entered, Winnipeg is also seeing fewer thunderstorm days on average in the 1991-2020 normals. On average, there are now 24 days per year with a thunderstorm at the Airport, a drop from the average of 26 days in the 1981-2010 normals. It is difficult to confirm whether the new average of 24 days is unprecedented because data prior to the 1970s is limited. The thunderstorm season is also a week shorter now, with the first thunderstorm (May 1) occurring four days later on average, and the last thunderstorm (Sep 28) occurring four days sooner. The largest drop in activity has occurred in the spring and summer, with fall seeing mostly unchanged thunderstorm frequency.
Humidity
Winnipeg has become slightly more humid in the 1991-2020 normals with the yearly average dewpoint rising from -1.7°C to -1.6°C. This small change, however, masks the monthly changes. Related to cooling temperatures, February to April has seen a drop in dewpoint. However, dewpoint has risen steadily in the summer, fall and early winter when it would be more noticeable. The rise in average dewpoint has been due to a combination of losing the drier 1980s and continuing the higher humidity seen in the late 1990s and 2000s. In fact, The 2011 to 2020 period had the second most hours (1604 hrs) with humidex above 40, behind only the 2001-2010 period (2385 hrs). In addition, the return period for dewpoint over 25°C has increased from once in 5 years to once in 3 years.
The rise in humidity is also evident when looking at the number of dewpoint records broken. The 2011 to 2020 period had the most high dewpoint records and least low dewpoint records of any decade since 1953. In fact, the proportion of dewpoint records being record highs instead of lows increased to a remarkable 3.3 to 1. This means for every record low dewpoint that was broken, there were at least three record high dewpoints.
Looking toward the 2001-2030 normals
The next normals will come in 2031 with the introduction of the 2001-2030 normals. Looking ahead, it is likely that Winnipeg's climate will continue to warm. In fact, it is unlikely that the yearly mean temperature will continue to remain stable. This is because of the loss of the 1990s which were the coldest decade since the 1980s. Of course, this is assuming that continued global warming will result in a warm decade in the 2020s for Winnipeg. Looking at individual months, January, July, November and December are the most likely to warm due to losing the colder 1990s. In fact, January has the potential to warm by as much as 1°C depending on what happens in the 2020s, which would result in average highs rising above -11°C and average lows above -21°C for the first time. July has significant warming potential as well, with July highs in the 1990s being the coldest on record. Highs are likely to average well above 26°C, assuming 2020s Julys aren't cold.
Conversely, February has the greatest cooling potential. In fact, February cooling could cancel out most of the January warming with possible cooling by as much as 1°C. This is due to losing very warm Februarys in the 1990s, such as 1991, 1992, 1998, 1999 and 2000. With January warming and February cooling, both months could be almost identical in terms of mean temperature. April could continue cooling as well if the cooling trend starting in 2013 continues. In other months, the signals are not very clear and depend primarily on what happens in the 2020s.
As for precipitation, it is always hard to predict. We have been in a dry cycle the past decade and it's nearly impossible to predict when we will return into a wet cycle. However, the 1990s were the 3rd wettest decade on record, which brings a higher likelihood that Winnipeg's climate will continue to become drier in the next normals, with summer drying the most. Of course, this depends on what happens in the 2020s. If the dry cycle continues for much of the 2020s, it is also possible that there will be some very hot summers to come, given the fact the current dry cycle is the most intense since the 1920s-1930s dry cycle. That cycle featured some of Winnipeg's hottest summers on record.
