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Will September’s wet weather continue?

You’d think it also would’ve been a colder-than-average September, but no

Last issue I talked about the rain — and no, it is not my fault that we received even more rain before the month of September was out, so quit blaming me! Now that the rainiest September on record for a large portion of southern Manitoba has come to an end, it’s time to take our monthly look back, then take a look ahead at the medium-length forecasts to see if this wet weather is expected to continue in October.

Before we get started, I thought I should share a little bit of information about forecasting accuracy that I picked up just the other week. Thanks to the computer modelling of weather getting better over time, weather forecasts have got better by about a day for every decade over the last 50 years. This means that today’s five-day forecast is about as accurate as a one-day forecast back in the early 1970s. While today’s two- to three-week forecasts are not perfect, they usually do a pretty good job of predicting the general trends in the weather over those time frames.

OK, now on to our look back at this wet, wet, September. As I discussed in the last issue, Brandon had already broken its all-time record for September rainfall and Winnipeg was closing in. Well, by the time the end of the month rolled around, both Brandon and Winnipeg racked up even more rainfall, which meant Brandon absolutely shattered its record, with Winnipeg just nudging past its record, as shown in Table 1 above.

 

I also dug through the rainfall totals from the Manitoba Agriculture weather program; Table 2 below shows some of the largest totals I could find for this September.

 

These are some truly amazing amounts, not just for September, but for any month of the year. Looking back at the records for wettest month ever recorded, most stations landed in the 220- to 250-mm range, so this September was truly a wet month.

Looking back at the temperatures in September, you would think that with all the rain and clouds it would have been a colder-than-average month, but it wasn’t. Thanks in part to the unique heat wave we experienced around the middle of the month, mean monthly temperatures at all three regions came in near to slightly above average. Winnipeg had a mean monthly temperature of 13.5 C, which was about 0.8 C above average. Dauphin’s mean monthly temperature of 12.7 C, a full degree above average. Brandon was the cold spot, with a mean monthly temperature of 12.1 C, or 0.3 C above average.

Who called it?

Overall, September 2019 turned out to be a little warmer and much wetter than average. Looking back at the medium- to long-range forecasts for September, it turns out that NOAA’s forecast was the closest, with a call for near- to above-average temperatures and above-average rainfall. Now let’s move on to October’s latest forecasts.

Starting with the almanacs, since their forecasts don’t change once they have been issued: the Old Farmer’s Almanac calls for a warm and dry October, which would be greatly appreciated by pretty much everyone. The Canadian Farmers’ Almanac appears to call for near- to slightly below-average temperatures as it mentions several cool to cold periods with a couple of mild periods thrown into the mix. It looks like it calls for near- to above-average precipitation as it mentions stormy, rainy, and even snowy weather several times, but then, it mentions dust storms across the Prairies at the end of the month, which would require very dry conditions.

Next on the list are the weather models, starting with last month’s winner: NOAA is predicting near- to below-average temperatures with above-average rainfall. I hope they get it wrong this time. The CFS model also calls for below-average temperatures and near- to above-average precipitation. The Canadian CanSIPS model forecasts a bit of a repeat of September, with above-average temperatures and precipitation.

Last is my interpretation of the different forecasts. I am leaning toward October seeing near- or maybe a little-above-average temperatures along with wetter-than-average amounts of precipitation. We will likely see a month with several warm spells interspersed with cold periods that will equal out as near average. This seesaw battle of temperatures will usually be accompanied by storm systems that will bring several chances of significant rain and maybe even a little snow later in the month.

Now as usual, we must sit back and see just what Mother Nature will throw at us this time.

About the author

Co-operator contributor

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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