Ag Weather Forum

Warm Eastern Pacific Ocean May Influence W. Canada

Doug Webster
By  Doug Webster , DTN Senior Ag Meteorologist

The winter weather pattern across North America has been persistent after the mild El Nino-like December pattern faded. One might wonder if the Madden Julian Oscillation (MJO) helped bring about the El Nino-type warmth during December, as well as possibly influencing the first half of March with some partial breakup of the upper air pattern for most of January and February.

As we head into the second half of March and the MJO has returned into the sectors that favor colder weather for eastern North America, we see the same upper air pattern of February resume across the Pacific, North America and the North Atlantic.

The MJO is an eastward propagating area of convection in the tropics that tends to disrupt and push northward the polar jet stream position if the MJO is strong enough. It is possible that during December the MJO helped push the jet stream northward and allowed Pacific air to flood southern Canada and the U.S. A weaker MJO passed by our longitude earlier in March and may have done so again, but with fewer results, due to the weaker nature of the most recent MJO.

Another piece of the puzzle appears to be warmer-than-normal sea surface temperatures (SST) across the eastern Pacific Ocean from the central coast of Mexico to the Gulf of Alaska. Kind of like the chicken-or-the-egg story of which came first, does this warmth help induce the upper level ridge across western North America or is the ridge what helped bring about the warmer SSTs?

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Looking back three years, we find that a large pool of warm SSTs has moved slowly eastward each year from the west-central Pacific in 2013 to the east-central Pacific last winter and now has made its way to the eastern Pacific for this winter. Last winter's cold pattern and snow was centered more in the central U.S. and south-central Canada, while this winter we saw the same conditions develop across the eastern U.S. and southeast Canada. The eastward shift in the core of the cold and snow mimics the eastward shift of the warm pool of the Pacific SST warmth.

The Prairies have had some cold weather this winter, but not nearly as harsh as the past two winters and it appears the spring is already making inroads on some areas. Snow cover has all but disappeared from the southwest third of the Prairies in places that saw snow cover last into early May last year. It is early and snow can still fly for a few more weeks, but the weather pattern may be stuck in the same pattern we have seen for much of the winter.

This weather pattern of a western North America ridge is not the best pattern to get precipitation for Western Canada even though some occasional periods of precipitation can fall as cold air backs in from the northeast. With the snow cover less than last year and already gone for some areas, one wonders if drier-than-normal conditions could develop and expand as we move through spring into the seeding season.

The eastern Pacific warm SST pool could be a player in this and could produce a spring and growing season quite different from what we saw during the past two seasons. Could the ridging pattern that seems so persistent across western North America bring us dry conditions along with above-normal temperatures as we move deeper into spring, or will the western ridge deflate at some point and allow some Pacific storminess to cross the Rockies?

Despite having a fairly poor and late start to seeding during the past two years, a very favorable crop was harvested across the Prairies. The questions this year are will a much earlier start to spring and drier conditions have some impact on this year's crop, and how much impact will it be? Some of the answers to these questions could be floating in the warm waters of the eastern Pacific.

Some of the climate models that produce forecasts for the next few months indicate that above-normal temperatures may continue for western North America, including the Prairies, into summer. Do these models see the effects of the eastern Pacific warm SST values or do they key in on weather pattern persistence? Answers to many of these questions will begin to show up as we move through the next few weeks in what is shaping up to be a very interesting weather pattern for North America.

Doug Webster can be reached at doug.webster@dtn.com

(ES)

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