A review of February's weather across North America, particularly Western Canada, shows some fairly extreme conditions prevailed with little change for much of the month.
Monthly average temperatures across the Prairies stood at about 0.5 degree Celsius (1 degree Fahrenheit) above normal across Alberta, 4 degrees C (8 F) below normal for Saskatchewan, and 6 degrees C (10 F) below normal for Manitoba.
Even colder weather departures were noted across southern Ontario to southern Quebec and exceeded 8 degrees C (14 F) in some places. The upper air pattern was stuck in place all month long with the central and eastern portion of Canada covered by arctic air. Far Western Canada saw some cycling back and forth between cold and milder readings, which is why Alberta was much more moderate than locations farther east.
A look back at the Northern Hemisphere upper air charts shows one big reason why eastern North America saw record cold and snow for many areas. A very strong upper level ridge remained planted in the vicinity of and just to the west of the Azores all month long. This ridge acted like a road block to the normal east-to-west progression of the long wave troughs that we normally see.
An analogy to best describe what happened would be white water rafting. When one is white water rafting, the raft typically goes over a series of waves and troughs within the river that rise above a rock formation then fall into a trough, then rise again over a wave atop the next rock formation. These waves are created by the rock formations under the water and remain in place as standing waves.
We did not have rock formations that created the February weather pattern, but we did have a standing wave situation from the Atlantic Ocean west across North America into the Pacific with respect to the upper air jet stream flow pattern. An anomalous upper level ridge stayed stuck near the Azores for nearly five weeks representing the wave going over the rock formation. A trough stayed in place across the eastern half of North America while another ridge was placed near the west coast of North America. Another trough was in place through the central Pacific during this time as well.
These long wave features acted as standing waves for nearly a five-week period with the short wave energy passing along this jet stream flow. Instead of high latitude blocking like we saw last winter, we saw mid-latitude blocking this winter. It just so happened that the position of the trough across North America was also a big cold air maker. Arctic air was continuously being made across most of central and eastern Canada and being delivered southward across the eastern half of the U.S. Most of the Prairies were stuck in the cold, while Alberta saw brief periods when the Pacific air brought some relief. The western half of the U.S. saw near record warmth as it was stuck under a ridge.
This boundary through the western Prairies also helped bring increased snowfall for the region last month. All three Prairie provinces observed above-normal precipitation and snowfall by as much as 150% and more in some areas. Early winter snow depths were depleted by very warm weather during December so some added snow for some early spring soil moisture when the snow melts was probably a good thing for most areas.
During the past week we have seen the roadblock standing wave weather pattern break down and a resumption of the west-to-east motion of large scale weather systems has resumed. This means that an end to persistent cold is likely for all of Western Canada during the next several days and a more typical changeable temperature pattern is likely for the next few weeks. Some additional snows are likely as the weather fluctuates from cold to mild. It is still a little early to decide when spring really breaks out to allow for early fieldwork to begin, but it is encouraging to see the stalled weather pattern of February break down into a more normal weather regime for Western Canada for this time of year.
Doug Webster can be reached at email@example.com
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