Last issue we took a quick look at the atmospheric and oceanic phenomenon know as La Nińa, or, as we pointed out last issue, the anti-El Nińo. Now that we have a bit of an understanding of La Nińa let’s take a look back and see what kind of winters we’ve had the last few times there was a La Nińa event.
Before we go into this, I have to throw in my usual disclaimer. If long-range forecasting was as easy as simply looking backward to see what happened when similar conditions prevailed, our long-range forecasts would be a heck of a lot better than they are now!
The problem with this type of forecasting is, while the general weather conditions were similar, they are never exactly the same – not even close. As we’ve discussed and examined several times in the past, even a small change in conditions over a relatively small area can change the weather dramatically. On the other side of the forecasting coin is the idea ofpersistence, the notion that the atmosphere tends to behave in similar ways under similar circumstances, kind of like the weather having a memory. It’s because of this second reason that we are taking a look back at previous La Nińa years to at least give us some idea of what this winter may be like.
Looking back over the last 30 or so years, I discovered that the Pacific Ocean has undergone about six medium to strong La Nińa events in the following years: 1975-76, 1988-89, 1995-96, 1998-99, 2000-01 and 2007-08.
For this study I looked at the average monthly temperatures and precipitation at six different locations across the Prairies (Edmonton, Calgary, Saskatoon, Regina, Brandon and Winnipeg) for the months of November through March. I then compared the monthly temperatures and precipitation amounts at each of these locations to their long-term averages, to see if the months were both colder/warmer and drier/wetter than average. I also averaged out the weather over these five months to create a value for what I call the extended winter season across the Prairies, and did the same type of comparison.
If you were to look up La Nińa and its typical effects
on western Canadian winters, the literature would indicate we should expect to have a colder-and wetter-than-average winter. Keeping this in mind, this is what I discovered when I looked at the data for all six centres for the extended winter season. Apparently, if you live in Saskatoon or Edmonton, you have an even slightly better chance of having a milder-than-average extended winter during a La Nińa year. In Calgary, four of the last six La Nińa winters actually ended up being warmer than average, so our textbook description of a La Nińa winter doesn’t seem to hold up at these locations, at least in regard to temperatures.
The textbook description of a La Nińa winter does hold up in Regina, Brandon and Winnipeg. All three of these
centres had statistically greater numbers of colder-than- average winters during previous La Nińa years. In fact, Brandon only saw one warm winter during the past six La Nińa events.
Precipitation during La Nińa winters also doesn’t seem to exactly follow what the texts say should happen. When it comes to winter precipitation during these years, it seems like it is east versus west. In Manitoba, the two centres had a significantly greater chance of a wet winter, with both Winnipeg and Brandon recording four wet winters out of the six La Nińa winters. As we move into Saskatchewan and Alberta the numbers reverse themselves, with most centres recording only two wet winters during those same six winters.
When I looked at the monthly values I didn’t see any clear-cut trends across the Prairies. I guess if I had to try and pull one interesting thing out of the monthly data, it’s that during La Nińa winters, there appears to be a better-than-average chance of having a cold and snowy December. To me that means an early start to the ski season and a good old-fashioned Christmas!
Overall, if you are in the eastern Prairies it looks like we’ll see a cold and snowy winter. Further west it’s not as clear, but if I had to make a prediction I should logically go with the stats and say “warm and dry,” although my gut is telling me “cold and snowy.” No matter which way it turns out, not everyone will be happy.