Ag Weather Forum

High Latitude Blocking Brings the Big Chill to W. Canada

By Doug Webster , DTN Senior Ag Meteorologist
The extended range forecast for the next two weeks provided by the U.S. National Centers for Environmental Prediction show a very cold scenario for central and Western Canada during the next week before the chill shifts to eastern Canada and allows the west to moderate during the second week. (Graphics courtesy of U.S. National Centers for Environmental Prediction)

During last week's post we eluded to the possibility that some high latitude blocking could return to Canada and Greenland during the middle of January, but that this was not set in stone. El Nino has been mostly the ruling party across North America during the early winter giving Western Canada mostly above-normal temperatures on average; it was colder than normal later in December.

As the days have progressed we have seen more computer generated forecasts jump onto the pile suggesting that we are likely to see a disruption with the El Nino induced weather patterns across Canada and the northern U.S. during the mid-January period.

Even before the true blocking pattern takes place we will see a generous supply of arctic air push southward into the Prairies during the coming days reversing the currently milder-than-normal readings to below- and well-below normal by this weekend into early next week. This comes about due to a ridging pattern through the eastern Gulf of Alaska that is blocking the advance of modifying Pacific air and allowing arctic air to collect across northwest Canada.

As we move deeper into next week the true block will begin to develop as an upper level ridge across the North Atlantic builds northward to Greenland and grows quite strong eight-to-10 days from today. This pattern will force the polar vortex to be displaced from northern Canada to eastern Ontario and Quebec which is a pattern that pulls arctic air southward to cover a large chunk of Canada. Below- to well-below-normal temperatures are a typical result for western and central Canada with such a pattern.

This evolving pattern could have enough legs to negate the warm weather forecast that has been consistently forecast for much of Canada for January. The answer as to whether January turns out to be at least a normal month temperature-wise for the Prairies will lie in how fast or possibly even whether the blocking pattern breaks down or weakens late in the month.

Most of the computer-generated forecasts show the cold pattern weakening after about a week of severe cold, but experience says that these patterns sometimes linger a little longer. Past experience also tells me that when it turns cold in such a pattern that sometimes it can be colder than some of the initial forecasts show, so be prepared to see future temperature forecasts drop to colder levels.

The accompanying forecast charts for the next two weeks are provided by the U.S. National Centers for Environmental Prediction. They show a very cold scenario for central and Western Canada during the next week before the chill shifts to eastern Canada and allows the west to moderate during the second week. If this forecast is wrong, it may be more be that it does not make it cold enough during the first week forecast and it removes the cold air too fast for week two.

Eventually the blocking pattern will probably weaken or dissipate late this month or during February, but high latitude blocking can have a life of its own and can even disrupt the current strong El Nino that has been on display so far this winter for the U.S. and Canada.

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

(ES)

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