ENSO or El Nino/La Nina-Southern Oscillation is a band of anomalously warm or cool water that develops off the western coast of South America and causes climatic changes across the Pacific Ocean. These include changes to surface pressures with the warm phase or El Nino producing high surface pressure through the western Pacific. The cold phase or La Nina brings accompanying low pressure to the western Pacific.
While there continues to be a great amount of study on these oscillations and how they work, scientists do know that the effects extend well beyond the tropical waters of the Pacific Ocean. Droughts, flood, cold and hot weather develop across other parts of the globe thousands of miles from the tropical Pacific that seem to have a relationship to either El Nino or La Nina. So what kind of a climate is produced for the Canadian Prairies?
The warm episode of El Nino typically brings mild winters with near- to below-normal precipitation to the Prairies while the opposing state La Nina favors low temperatures with precipitation levels closer to normal. One would expect that a La Nina has been in place so far this winter, but the data says we have mostly been in a neutral ENSO state. This means the water temperatures have mostly been near normal across the tropical Pacific. In fact, at times the ENSO state has favored a weak La Nina. So why has the winter weather been much more like a La Nina winter?
There are other complicating factors that influence on our climate and one of them that may be playing a role this winter is the Pacific Decadal Oscillation or PDO. The PDO has been in a negative or cold phase for nearly a decade now and tends to favor chillier weather across Canada. Since the ENSO state has been mostly neutral so far this winter, it seems that the Pacific Decadal Oscillation and possibly its Atlantic cousin, the Atlantic multidecadal oscillation (AMO), has had a greater say in the state of Canada's climate.
Unlike last winter, when mild temperatures and no upper level roadblocks developed across Canada, we have seen periods of high latitude blocking across Eastern Canada and Greenland which leads to cold weather for Western Canada. More than likely the ENSO effects have been mostly minimized or negated because of the neutral ENSO state allowing the northern latitude climate oscillations to exert a greater influence.
Current longer range forecasts bring a return of cold or very cold weather to the Prairies into early and mid March. There also appear to be few opportunities for precipitation during the next few weeks which lead to concerns about available soil moisture once we reach the spring planting season. Time will tell whether we see some late winter/early spring precipitation recovery or if we start out the growing season with less than adequate soil moisture conditions.
While ENSO seems to have some affect on Western Canada's climate during many years, this year it appears to have less impact.
Doug Webster can be reached at firstname.lastname@example.org
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