Nearly a world away, across the tropical Pacific, warmer-than-average sea-surface temperatures have warmed to levels seen just a few times during the past century. This phenomenon known as El Nino occurs every several years or so and is caused when the normal east-to-west trade winds across the Pacific weaken or even come to a stop.
The normal transport of warm waters from the eastern to the western Pacific is disrupted, allowing the central and eastern Pacific to warm by as much as several degrees C. Sea level is also affected with the warmer eastern Pacific seeing higher levels and areas across the southwest Pacific seeing lowering sea levels during an El Nino.
This year's El Nino is one of the stronger ones observed during the past century and is shown nicely on the accompanying sea surface temperature anomaly chart as a strip of red extending westward from the northern South America coast near the equator. The impacts of an El Nino are long known to have worldwide effects on weather.
Canada is one region that typically sees sizable impacts during an El Nino. The jet stream flow across North America is disrupted in a manner so that the western half of Canada tends to stay in a westerly flow of Pacific air much more of the time during the winter season. El Nino's effects on eastern Canada tend to be less and sometimes northeastern Canada can even be on the cold side of normal during an El Nino.
So far during the late summer and fall we have seen weather patterns that fit quite nicely into what an El Nino should produce. Lots of westerly flow from the Pacific and more often than not temperatures have been on the mild side of normal. Rains returned during the last summer and early fall as a result of a series of low pressure areas moving from the Pacific across southern Canada.
Most of our weather computer models continue to show this kind of weather pattern lasting during October into November with the El Nino expected to peak during December. For the most part, the El Nino weather pattern has been a help to harvest this fall, providing mild weather and mostly short-lived rain events. While the rain events still bring a halt to harvest for a time, the spacing in between is enough so that harvest progress for most areas is still ahead of normal.
The El Nino induced weather pattern has kept significant cold out of western Canada with season-ending frosts and freezes coming later than normal this year and there are still a few spots that have yet to have a freeze. Harvest of some crops is wrapping up and most of the harvest should be in the bin within two weeks for all areas.
We do not see any major disruptions coming along to delay or disrupt harvest for more than short periods during the next week or more and many areas will continue to enjoy milder than normal temperatures most of the time. The westerly jet stream flow from the Pacific into Canada keeps any cold air trying to develop across far northern or northeastern Canada most of the time. Lacking for cold air production in this fall's weather pattern is a strong ridge through western North America which blocks Pacific air from entering Canada and allows arctic air to develop across the soon to be expanding snow cover.
Doug Webster can be reached at firstname.lastname@example.org
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