Sunday, November 15, 2015

Very mild start to November as extended autumn continues.. but change to colder weather on the way this week

It was another glorious fall-like weekend across southern MB with sunny skies and temperatures in the double digits. Sunday's high of 13.1C in Winnipeg was almost 15C above normal for Nov 15th, and was our 21st straight day above normal (since Oct 26th). The weather was par for the course in what has been an exceptionally mild start to November across much of central and eastern North America, especially over the upper US midwest and central Canada, including southern MB. In Winnipeg, the average temperature over the first half of November has been +3.3C, which is almost 6C above normal for the Nov 1-15 period.  Every day this month has been above normal so far and the coldest temperature this month has been only -6.4C, even though normal lows are now close to -10C. The downside of the mild weather has been frequent cloud cover, with only 4 days of sunshine through the first 12 days of the month. Snow however has been virtually absent in Winnipeg, with only a couple days with some light flurry activity. As of mid November, the grass is still green in the city thanks to a lack of deep freezes so far.

Figure 1 (left): Mean temperature and anomaly from normal (C) showing core of exceptional warmth this November over upper midwest  
Figure 2: (right) Winnipeg mean daily temperature past 30 days (Oct 16 - Nov 15) showing persistence of above normal temperatures over past 4 weeks

As mild as it's been, it may be surprising to learn that Winnipeg has had even milder starts to November in previous years. At 3.3C, the first half of November this year will rank only as the 8th mildest start to November since 1872. The warmest start to November (as defined by the mean daily temperature from Nov 1-15) was in 1981 and 1931, with an average temperature of +4.9C over the first half of the month.  Nov 1981 saw 10 days reach +10C or more in the first half with a peak of 18.2C on Nov 4th.  This year, Winnipeg has recorded only 4 days in November of +10C or more. This shows that our warmth this year has been mainly due to exceptionally mild nights, rather than mild days. Frequent cloud cover and lack of cold air intrusions has resulted in a persistence of mild nights with temperatures well above normal minimums for November. The top 10 warmest first halfs of November in Winnipeg since 1872 are:

So what does the rest of November look like? Well, mild weather is expected to continue the first half of this week, then a pattern change around mid week as a strong storm system brings a substantial cool down later this week with temperatures likely falling below normal for the first time this month. We may even see our first shot of accumulating snowfall here in the city Wednesday night into Thursday. Colder than normal temperatures will dominate through next weekend before a moderating trend next week.

Multi-model ensemble shows big temperature dip coming to
Winnipeg by Thu Nov 19th (850 mb temps top)
The transition to colder weather will likely be accompanied by
our first snowfall Wed night into Thursday  (precip amts bottom)


  1. Hey Rob,

    Do you think the system coming will bring any significant snowfall to Winnipeg?

    1. Depends what you mean by "significant". I think we'll be seeing our first general snowfall with probably 5 cm or so on the ground in Winnipeg Wednesday night into Thursday, not a lot but certainly enough to cause problems given it will be the first widespread snow of the season, along with strong winds that will give slippery road conditions and locally poor visibilities in snow and blowing snow. Heavier amounts (10 cm or more ) are possible in the Interlake and SE of Lake Winnipeg due to bands of heavier lake effect snow. Updated info on system just posted on blog.