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Past Weather Does Not Always Mean Future Weather

Early in September I took a quick look at the kind of weather we might expect this winter. In particular, we examined the phenomenon known as La Nińa or the “anti El Nińo.” La Nińa is a cooling of the equatorial Pacific Ocean and when this occurs it can have an impact on our winter weather.

This year the Pacific is undergoing a medium to strong La Nińa, which means there is a fairly strong likelihood that it will affect our winter weather. Maybe this is why there are so many long-range winter forecasts coming out this year. It seems that everyone has an opinion on what this winter’s weather is going to be like, and they all seem to be reading from the same book.

If you do a little research on La Nińa and winter weather in North America, what you will tend to find is that southern regions have a greater chance of being warm and dry, while northern regions are colder and wetter – which means lots of snow. The problem with this is that it is a pretty broad brush stroke to try to paint the winter weather picture. As I pointed out back in September, over the last six La Nińa episodes, Western Canada did not always follow this textbook description of a La Nińa winter. In fact, if you remember, the western Prairies saw more mild and dry winters during La Nińa years, while the eastern Prairies saw more cold and snowy winters.

If we were to look at a map of temperature and precipitation anomalies during the last strong La Nińa events (1999-2000 and 2008), we would see that during those winters, most of the United States and the southern half of Canada saw above-average temperatures. Precipitation during those winters was around average in our part of the world, with wetter conditions out east and along the West Coast.

So to me it seems as if we have a bit of a contradiction, we are being told La Nińa winters bring cold, snowy weather, yet the data for our part of the world doesn’t seem to totally support this fact.

PAST IS NOT FUTURE

Now unfortunately, as I have pointed out many times, long-range weather forecasting is not as simple as looking back to see what other similar years have been like. In fact, while short-range weather forecasting has become much better over the years, long-range weather forecasting has still pretty much a 50-50 chance of being right. The problem is that no matter how good computers get, they are only as good as the information that is given them to start off with, and we simply can’t measure all of the factors that need to go into the weather models accurately enough or in enough detail (spatial coverage).

The other problem is that there is not one thing, like La Nińa, that entirely controls the weather. It can have a strong influence on weather patterns, but there are always other factors that can effect the weather. Take what is going on in the Arctic for example. NOAA (the U.S. weather agency) issued its annual Arctic Report Card last month, and discussed the fact that recent record sea ice loss in the summer in the Arctic is having major impacts on winter weather over the continents of the Northern Hemisphere. The report card states, “There continues to be significant excess heat storage in the Arctic Ocean at the end of summer due to continued near-record sea ice loss. There is evidence that the effect of higher air temperatures in the lower Arctic atmosphere in fall is contributing to changes in the atmospheric circulation in both the Arctic and northern mid-latitudes. Winter 2009-10 showed a new connectivity between mid-latitude extreme cold and snowy weather events and changes in the wind patterns of the Arctic; the so-called Warm Arctic-Cold Continents pattern… With future loss of sea ice, such conditions as winter 2009-10 could happen more often. Thus we have a potential climate change paradox. Rather than a general warming everywhere, the loss of sea ice and a warmer Arctic can increase the impact of the Arctic on lower latitudes, bringing colder weather to southern locations.”

So it seems that we may be heading into some new uncharted winter weather territory, and just like when you explore, you just never know where you will end up!

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