Ag Weather Forum

Weather patterns across North America -- and for that matter much of the Northern Hemisphere -- have undergone some retrogression during the past week or so. Retrogression is nothing more than backing up of the main weather features controlling the surface weather patterns shifting westward rather than eastward.

If you live through Saskatchewan or Alberta you have probably noticed temperatures are a whole lot colder this week than they were about a week ago. This is due to the westward shift of the blocking ridge across Alaska to eastern Siberia, allowing the trough and associated polar vortex across Canada to wobble west enough to include the western Prairies within the envelope of arctic cold. Manitoba has pretty much been in the very cold regime right on through the later portion of January into February.

Still alive is the cold air manufacturing mechanism across North America despite the slow westward shift to upper air features. The reason is that, even though the ridge through far western Canada is mostly gone, the main jet stream flow is moving in from the Pacific across the West Coast of the U.S. and not across western Canada. That's why we are seeing dry weather from coast to coast across Canada and storminess at the moment is moving into the northern half of the U.S. West Coast.

Without that push of Pacific flow into western Canada, temperatures will not moderate and arctic high pressure will remain dominant, keeping temperatures very cold. But there is hope on the horizon for some change. We think by the middle or end of next week we may see some increased flow of air from the Pacific as a trough slowly deepens from the Gulf of Alaska, southward. This deepening trough may allow the jet stream to begin to push into at least the southern half of the British Columbia coast, helping to bring modifying temperatures and a little bit of moisture.

Instead of storms traveling into the Pacific Northwest of the U.S., we should start to see low pressure push into the central British Columbia coast and then jump over the mountains to the southern Prairies. This pattern would allow the western and southwestern Prairies to warm back to more seasonable levels and also bring some precipitation. Cold air might hang on for the eastern and northeastern Prairies where an overrunning precipitation pattern could produce increased snowfall. If this sounds like it has happened before, it did, during the middle of January.

As for a complete change or reversal to the mostly cold weather pattern we have seen thus far this winter, we do not see that coming soon. The changes expected next week will be subtle and are expected to bring the most relief from the cold to western areas. We are still dealing with the pattern across the Northern Hemisphere with the more dominant polar vortices on the North America side rather than the Asian side. This has been the case since last March and could allow cold weather to return to even western areas later this month or March, if one or two large-scale features across the Northern Hemisphere shift a little bit again.

The day length is increasing at a steady pace and temperature normals are on the rise. Unfortunately, the weather does not always follow the route the sun and long-term temperature averages tell us they should. Last spring is a good example of that with winter weather extending well into the spring and delaying planting. We can only hope that winter will release its grip sooner this spring to allow for field work and planting to commence at a more reasonable time.

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

(ES)

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