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December To Follow November’s Pattern?

Before we dive into our monthly look back at the weather, I think I need to clear up a misunderstanding from the “probability of snow” article from a couple of weeks ago. A fair number of people have emailed me asking if there is such a low probability of getting more than 10 cm of snow in a day or during a snowfall event during the winter, how come we have already seen two or three of these events already this winter?

Well, there are two answers for this. The first one is that for the calculation I used to determine the probabilities, I used precipitation data that was measured as the amount of water the snow would melt down to. From this, I used the standard conversion ratio of 10:1. This means that 10 mm (one cm) of snow would equal one mm of water. While this might be the textbook standard conversion, in reality, we rarely see this in our part of the world. Typically we see ratios around 15:1 and it can be has high as 20:1.

So, if we take a look back at the snowfall in November, Winnipeg did not record more than 10 mm of water equivalent on any given day, but did record more than 10 cm of snow on a couple of days. In my probability calculations these events would not have been seen as more than 10 cm of snow. I think sometime this winter I will rerun the probability calculations with a conversion ratio of 15:1 and see how the numbers come out.

The second answer is that these are probabilities and while they tend to help us understand how often we should see different snow events happen there is nothing that stop us from having many more or less than what the probability indicates.

OK now on to our monthly look back, and then forwards, at the weather. After an extremely warm first couple of weeks of November, winter finally decided to move in, and by the 13th of the month the mean daily temperature fell below freezing and stayed there for the remainder of the month. While the second half of the month was cool it was not overly cold, and when all the numbers were added up all three regions (Dauphin, Brandon, and Winnipeg) recorded above-average temperatures.

Brandon was the cool spot with a mean monthly temperature of -5.2 C, only 0.5 C above average. Winnipeg came in second, with a temperature of -3.3 C a full 2 C above average. Dauphin was the warm spot with a mean monthly temperature of -0.4 C which was more than 5 C above average.

Precipitation for the month was also above average across all three regions. Dauphin recorded the lowest amount of precipitation with 27.4 mm, Winnipeg came in next with 31.5 mm, and Brandon was the wet spot with 37 mm. This was the seventh month this year that we have seen above-average amounts of precipitation.

In fact, if we take a look at the yearly total precipitation amounts we would find that several places have either already broken or are very close to breaking their all-time yearly precipitation records. The Dauphin region may have already broken the 1953 record of 742.1 mm. The Environment Canada data feed for Dauphin has not been working correctly for the last several months, so I combined data from the first half of the year with Ag Canada’s data for Dauphin and I came up with total so far this year of 834.9 mm. Winnipeg is close to its record of 724.6 mm set back in 1962. So far this year Winnipeg has recorded 697.5 mm of precipitation, so if they see an above-average amount in December they have a chance at the record. Brandon has also been wet, with a yearly total of 591.8 mm, but this falls well short of the 692.6 mm record set back in 1975.

Who was able to best predict the warm, wet November weather? Looking back I would say that none of the forecasts were on the mark! Both of the Almanacscalled for colder-than- average temperatures with above-average amounts of precipitation. Environment Canada and myself called for warmer-than-average temperatures with below-average amounts of precipitation.

Will we see a cold, snowy December or will it be mild and dry? According to theOldand Canadian Farmers Almanacs December is going to have temperatures near the long-term average, along with above-average amounts of precipitation. TheCanadian Farmers Almanac(which called for thunderstorms in November) is calling for heavy snows over the Christmas holidays. Environment Canada is taking a different view of December’s weather as it is calling for below-average temperatures along with near to below-average amounts of precipitation.

Finally, here at the Co-operator,I am leaning towards theAlmanacforecasts. It is looking like temperatures will run pretty close to average, with the odd cold snap being followed by a mild spell. Precipitation forecasts are always tricky, but it is currently looking like the weather pattern will remain fairly active during the month and it only takes one good storm for us to come in around average for the month. Who knows, maybe we will see that big Christmas snowstorm this year!

About the author

Co-operator contributor

Daniel Bezte

Daniel Bezte is a teacher by profession with a BA (Hon.) in geography, specializing in climatology, from the U of W. He operates a computerized weather station near Birds Hill Park.



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