Friday, February 10, 2012

Warmer winters - the new "normal" ?

This past January was Winnipeg's 3rd warmest January on record, with a monthly average of -10.8C, 7C above the "normal" January average of -17.8C. It was also Winnipeg's 7th consecutive month above normal. But what is "normal" exactly and how is it defined? In the case of monthly average temperatures (the average of all the daily highs and lows during the month), "normal" is based on a 30 year average of monthly temperatures at that site, and are updated every decade. This is the standard definition of normal as defined by the World Meteorological Organization (WMO) and is the standard used around the world.

The table below lists the 30 year normals for Winnipeg over the past century for each winter month, as well as the winter season overall (defined as Dec-Feb period) The latest 30 year normals (defined by the 1981-2010 values in red) shows a significant warming trend over the past set of 30 year normals (defined by the 1971-2000 period in blue) This is because the updated normals now include some exceptionally warm winters from the 2000s, and have lost some cold winters from the 1970s. For example, the new "normal" for January will now be -16.4C, a full 1.4C warmer than the -17.8C average we've been using over the past decade. (Note: Environment Canada is still not officially using the updated 1981-2010 normals since they have a backlog of quality control to do on climate data. Until that is done, they will still use the 1971-2000 normals.) Looking further back, the new January average of -16.4C is almost 3C higher than the normal January value of -19.3C in the 1951-80 period. In other words, a normal January in the 50s, 60s and 70s would be considered 3C below normal now! Winters were definitely colder 30 years ago!

30 year winter normals - Winnipeg

30 yr period....... DEC ....... JAN ...... FEB.........WINTER (DJF)

1981-2010 ....... -13.5C .... -16.4C .... -13.5C ...... -14.5C
1971-2000 ....... -14.4C .... -17.8C .... -13.6C ...... -15.3C
1961-1990 ........ -14.7C .... -18.4C .... -15.2C ..... -16.1C
1951-1980 ........ -14.0C .... -19.3C .... -15.6C ..... -16.3C
1941-1970 ........ -13.7C .... -18.3C .... -15.8C ..... -15.9C
1931-1960 ........ -13.2C ..... -17.7C ..... -15.5C ..... -15.5C
1921-1950 ........ -13.6C ..... -17.5C ..... -15.4C ..... -15.5C
1911-1940 ........ -13.3C ..... -18.3C ..... -15.4C ..... -15.7C
1901-1930 ........ -13.7C ..... -18.2C ..... -15.6C ..... -15.8C
1891-1920 ........ -13.8C ..... -18.8C ..... -17.2C ..... -16.6C
1881-1910 ........ -14.6C ..... -20.1C ..... -18.4C ..... -17.7C
1873-1900 ....... -15.4C ..... -21.1C ...... -18.7C ..... -18.4C

Note also that the new 1981-2010 normal for December is almost 1C warmer than the 1971-2000 normals (again due to some very mild Decembers in the 2000s). On the other hand, February has remain relatively unchanged (-13.5C vs -13.6C) Put them all together, and "normal" winters in Winnipeg now average -14.5C, the mildest they've ever been since record-keeping began in the 1870s. (and +0.8C higher than the 1971-2000 winter normal)

The table also shows that winters in the 1920s, 30s and 40s were milder than the 50s, 60s and 70s. So this does show some sort of natural climate variability over the course of a century. However, the table also clearly shows that the past decade has seen some exceptionally mild winter weather that has made winters in Winnipeg the warmest in modern history. Will the trend to warmer winters continue through the 2010s, or will natural climate variability bring some colder winters back in our future? Let us know what you think in the latest Rob's Obs poll..


  1. Interesting that up until the 1971-2000 normals, February was always colder on average than December. December overtook Feb in the 1971-2000 period, and now the 1981-2010 normals have them the same, with both trending higher. Kind of shows that cold weather is starting later, and ending sooner, so winters appear to be getting shorter, on average.

  2. Rob, Check out your facebook page for some cool photos.

  3. Nice research rob, you can really tell our winters are getting warmer. I just hope that within the future Ill be able to post something like this on my blog once we get really unseasonable winter weather.....

  4. I think this year has been unseasonable enough, not one -30C or lower temp, only second time since records began.

  5. Final poll results:

    Climate change: 46%
    Natural variability: 31%
    Wait and see: 21%

    Most people (almost 1/2) think that the mild winters of the past decade are part of a discernible warming trend due to climate change. About 1/3 of respondents think it's just natural variability, and we'll see colder winters in the upcoming decade. 1/5 were not commital, and will wait and see what happens!

    Personally, I voted for climate change.. just too much evidence that our climate is indeed changing and trending upwards. But as usual, only Mother Nature will let us know the real answer.

  6. Hi, I have done some similar comparisons here in BC for the 1981 to 2010 normals. January has typically been the coldest month of the year in the Okanagan valley, however, the 1981 to 2010 climate normals now show that December is the coldest month of the year!

  7. An interest thread you might enjoy...