Ag Weather Forum

March saw a wide variety of temperatures across the Canadian Prairies. The first week to 10 days of the month saw a fairly cold pattern across the region, along with a significant snow event for some areas. The middle of March was much more seasonal in nature, with some cold and some warmer days, but nothing extreme. Then the last five days of March saw the deep freeze return, and this has continued during early April.

This pattern of extreme cold is due mostly to a high-latitude high-pressure blocking pattern, which was absent for a time during the middle of March, and returned at the end of March. The main blocking ridge set up between Alaska and Siberia, but a secondary blocking ridge also set up over northern Canada. The western ridge limited the moderating impact of the Pacific, while the northern ridge forced the polar vortex southward in Canada and led to the current extreme cold event. The continuing La Nina in the Pacific may have also contributed to the below-normal aspect of the temperature pattern, but the blocking was the main driving force.

Precipitation during March as a whole averaged near to above normal in west and south Alberta and through much of Saskatchewan, occurring mostly as snow. Precipitation averaged below normal in Manitoba and in Alberta, from near Edmonton towards the northeast and a little of Saskatchewan near this area. Precipitation in any form is mostly welcome as the region has been quite drive since last fall. There is not enough moisture in this snowpack to be overly concerned about a spring flood risk at this time, at least for most areas.

Short-range weather maps, covering the next 10 days, show some weakening of the high-latitude blocking pattern in Canada. The strong Siberia ridge is shown weakening considerably, while the northern Canada ridge moves to northern Europe. This weakening of the high-latitude blocking ridges allows the polar vortex to drift northward during this period. If verified, this would allow for a less severe weather pattern over the Prairies. It will be at least a few more days before the extreme cold eases up in the area. As the cold relaxes, this might allow moisture to move northward from the United States. This brings a chance for snow to many locations during the middle of next week. It will likely still be cold enough for this to be snow in the region. Moisture will generally be favorable, but for the upcoming summer growing season, more will be needed. The forecast through mid-April calls for temperatures to average near to below normal, with precipitation near to below normal west and north, and near to above normal over southeast areas.

The longer-range outlook for the Prairies depends mostly on two factors. The first is the gradual weakening of the eastern Pacific La Nina during the mid- to late-spring period. If realized, this should lead to a somewhat warmer and drier pattern later in the spring. This would favor spring fieldwork and planting, but may increase the risk to crops during the summer growing period if there is not enough moisture in the soils to support favorable development of crops.

The second factor is the high-latitude blocking pattern. As we have seen already, the high-latitude blocking has been in the picture more than it has been absent. Blocking during the winter months as it concerns the Prairies may not be the same as blocking during the mid- to late-spring or early summer periods. In the winter, a blocking pattern in the west and north leads to a cold and dry pattern in the Prairies. In the spring, this same blocking pattern might mean a more-variable temperature pattern, and a more-variable rainfall pattern as well.

Indications are that the most likely weather patterns for the Prairies during the balance of April would be for the current extreme cold pattern to give way to a temperature pattern featuring near- to below-normal temperatures. Precipitation chances will increase somewhat during the coming week as the now-active storm track in the U.S. attempts to move northward with time; however, the best chance for near- to above-normal precipitation would be in southeast areas of the Prairies. This would actually be good news, as this is likely the driest sector at the current time.

The early outlook for May calls for a further weakening of the Pacific La Nina, and therefore a warmer and drier outlook for the region. My feeling on the blocking pattern is for it to persist during the spring months, but in a weakened state. This suggests that the weaker La Nina would have more impact on the weather than the high-latitude blocking pattern would have during May. This should mean that planting season during May would start out slow, but would improve with time during the month.

Joel Burgio can be reached at joel.burgio@dtn.com

(ES)

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