The approach of a new school year heralds the gradual end of summer. So understandably, thoughts are turning to what weather to expect for the fall and winter.
While Environment Canada is predicting a warm, dry autumn and winter across the country, sources in the United States are warning the East Coast to brace for some strong snowstorms in January and February. Since weather in Ontario, Quebec and the Maritimes is closely tied to the Eastern U.S., residents in Eastern Canada could be in for the same powerful winter storms.
This would be a notable change from last winter, which has been deemed the "winter that never was," with warmer than normal temperatures and lower snowfall rates across the country.
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It was the second year in a row that the El Niño Southern Oscillation was in its La Niña phase, which typically means more snow across the country. But there also was unusually dry weather back in 1999/2000, which is the last time there were two La Niña years in a row.
ENSO is a pattern of ocean temperature changes in the equatorial Pacific Ocean. The "warm phase" of ENSO is called El Niño and is characterized by warmer temperatures off the coast of Ecuador and Peru and cooler temperatures off the east coast of Australia. La Niña is the "cold phase" of ENSO, when there are cooler temperatures off the coasts of Ecuador and Peru, and warmer temperatures off of Australia.
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These large-scale shifts in warm and cold water have a large impact on the weather in different parts of the world, Canada included. El Niño years are usually ones where winters are warmer and drier in Ontario, Quebec and the Maritime provinces, and wetter in southern British Columbia. La Niña years have slightly warmer winters, but are generally wetter across the country.
In 1999/2000 and for the past two years, another large-scale weather oscillation, called the Arctic Oscillation, had a big influence on our weather. It was in its "positive phase" during both periods, which changed up the normal La Niña pattern and resulted in dry weather.
With the prediction of an El Niño winter this year and the similarities between the last two La Niña events, we can take a glance back at 2001 for some idea of what to expect. However, whereas ENSO takes roughly 5 years to shift back and forth, the Arctic Oscillation can do that in a matter of a few days, so it's not easy to predict what it will be doing this winter.