ENSO, better known as El Nino-Southern Oscillation by climate scientists and meteorologists, can have some important effects on winter weather across the Canadian Prairies. Most of the time during an El Nino, or the warm phase of ENSO, we will see milder-than-normal temperatures and less-than-normal precipitation across western and central Canada. The mild, dry conditions are usually brought about by a jet stream that is located north of its normal latitude and an increased occurrence of drying westerly winds across Western Canada.
During a La Nina, or the cold phase of ENSO, we generally expect a cold weather pattern with increased opportunity for some precipitation events across Western Canada, including the Prairies. The upcoming winter season forecast for ENSO is for a mostly neutral pattern, neither warm or cold, so how may this forecast affect the Prairies?
Late-summer and early-fall forecasts were in general agreement that a weak or moderate El Nino was taking shape across the Pacific and that it would continue into the early winter before fading. During the past six weeks or so, the developing El Nino faded, which was not expected by most. Current climate models are forecasting a neutral forecast for the winter, if not a very weak La Nina.
Earlier in the fall we favored the idea of a winter that would be milder and drier than normal for the Canadian Prairies, which would have important implications for spring soil moisture conditions and spring crops. Given the current forecast, we have to shift gears a bit and give increased chances of colder weather at times along with a greater threat for precipitation. We've already had one good snow event last week and see signs that after the mild, dry period of the next week that a similar storm could bring sizable snow to some of the same areas toward the end of November.
A neutral ENSO pattern may lead us into a winter where we see changeable conditions. Alternating periods of cold weather with some decent precipitation may well be followed by drier, milder periods.
Cold air is expected to build across northwest Canada during the next 10 days and should slide down along the east slopes of the Rockies by the middle and end of next week creating an upslope wind condition. As this happens, we see potential of a new storm evolving through the northern U.S. Rockies which may expand heavier snows into at least the southern Prairies seven to 10 days from now.
Based on the current ENSO forecast, we would not expect the snow and cold to be persistent for the remainder of the winter, but for some periods of milder, drier weather to show up at times as well. It appears, at this time, that increased winter precipitation across the Prairies will improve soil moisture prospects for the spring.
Doug Webster can be reached at email@example.com