Scientists think that atmospheric blocking has become more frequent and may be lingering for weeks rather than days
Normally, June is the wettest month of the year in Manitoba.
But last June Brandon recorded 23 consecutive days with essentially no rain.
February is normally a cold month in Western Canada, but this February, Saskatoon had 13 days where the nightly temperature dipped below -30 C.
Such periods of persistent weather, where a drought, freezing temperatures or heat sticks around for weeks, are usually associated with atmospheric blocking.
“It’s a stationary pattern that sets up. It’s like an unwanted house guest. It won’t leave…. It just sits there,” said David Phillips, senior climatologist with Environment Canada. “You’ll get a high-pressure area that will just sit there like a rock in a river. It will force the flow, the circulation, to go around it, or below it.”
Atmospheric blocking is not new.
Meteorologists have been talking about blocks for decades. What is different, however, is they may be more frequent and may be lingering for weeks rather than days.
“We’re seeing these bouts of long-lasting events…. Instead of just one week, they go two weeks,” Phillips said. “It used to rain on a Thursday and be over on a Thursday. Now it’s raining on Thursday and it’s still raining on Saturday.”
Some meteorologists believe atmospheric blocks represent a fundamental change in the world’s climate.
“The new normal for all of the Northern Hemisphere, it seems, are these blocking highs,” Eric Luebenhusen, a U.S. Department of Agriculture meteorologist, said last month at a conference in Washington, D.C.
“If I had to give you a (weather) outlook … the theme for the spring is these blocking highs.”
If Luebenhusen is right, then lengthy periods of extreme weather may be more commonplace this spring and in the future.
So, three weeks with no rain in June and a month of freezing weather in February could become normal.
This concept remains a heated topic within the world of climatology, but recent data suggests that something has changed. For example, the extremely cold temperatures on the Prairies this February were unprecedented.
“There wasn’t a melting temperature on the Prairies (in February). I’ve never seen that before,” said Phillips, who has been studying the weather for more than five decades. “That could be related to this blocking situation. The (air) flow has changed.”
The big debate for climatologists is whether warmer temperatures in the Arctic are changing air flow patterns.
A few decades ago, the jet stream was typically a straight line from west to east, with cold air to the north and warmer air to the south.
Now, the jet stream meanders more across North America, going south and north haphazardly.
“We do know the jet stream has slowed by nine, 10, 12 percent, in say the last 20 years,” Phillips said.
Some scientists believe the jet stream is weaker because the Arctic is now warmer. The temperature gradient between the Arctic and warmer latitudes is smaller, so the jet stream slows down.
“The jet stream doesn’t have as much oomph,” said Phillips.
If warmer temperatures in the Arctic are changing the jet stream, it could create a new normal for weather in the Northern Hemisphere.
A percentage of climate scientists are not convinced this is actually happening, but others believe something has changed. Phillips is in the second group.
The evidence suggests something has happened, he said.
“We’re getting heat waves in the Arctic at the time that Winnipeg is freezing in the dark,” he said. “We saw more ice on the Great Lakes last year than we saw at the North Pole. Those things are head shakers.”
If Phillips and others who hold that view are right, then the warming of the Arctic could have a lasting effect on air circulation patterns in North America.
Which may mean more atmospheric blocks and more periods of “wacky weather,” Phillips said.
“I’m a convert. I really, truly believe the Arctic phenomenon is changing the circulation.”