Many variables make up our weather forecast

Some scientists call forecasting a chaotic system; that the tiniest factors at any moment can have a huge impact on the weather to come.

Environment Canada weather forecasters were sure off their game last weekend. They totally missed the three-day storm that dumped 53 cm of snow on much of Chilliwack. No doubt Sunday morning when the snow started to fall they were catching some zzzzz’s after watching another game – the gold medal hockey thriller in Sochi.

By the time the weather guys got a snowfall warning up on the EC website, snow was falling hard with east winds blowing at a good clip. But it was geographically variable. According to Roger Pannett, volunteer weather observer for EC, north of the Highway the snowpack was less than 50 per cent that of Garrison Crossing. Cultus Lake and Columbia Valley got a full blast.

Weather forecasting is a complex science involving thousands of atmospheric observations of pressure, wind, temperature, and humidity from ships, buoys, weather balloons and satellites. Some scientists call it a chaotic system – not that it’s out of control, but that the tiniest factors at any single moment can have a huge impact on the weather to come. One climate scientist on the U.K.’s Met Office website said that one flap of a seagull’s wings could change the course of weather forever. More poetically, it is call the butterfly effect.

Millions of these observations are fed into supercomputers capable of trillions of calculations a second. These computers then feed the outcomes into virtual models of the atmosphere based on the laws of physics. The further out they try to project the weather, the more wobbly the predictions become. But with the science at hand, a seven-day forecast is pretty accurately do-able. So last weekend’s inaccurate forecasting by the weather guys was a complete surprise, apparently even to them.

Nationally, forecasting the 2013-2014 winter has been pretty extraordinary with extreme and rare events that have got people asking, again, about climate change.

The polar vortex is back for the third time this winter across central and eastern Canada and the U.S. bringing with it severe cold. Manitoba and Ontario are looking at wind chills taking temperatures to minus 30C or minus 40C. And we are only three weeks away from spring!

Arctic air is usually kept in place by the jet stream, a west-east air current at about the altitude of jet flight that marks the boundary between polar air and warmer southern air.  But with the Arctic heating up faster than many other parts of the world the jet stream appears to be weakening, allowing the frigid polar air to leave its home base and slip further south.

The strength of the jet stream is proportional to the difference in temperature between the poles and the tropics. When it is strong, it has a straighter path but when it is weak it can meander in wider loops. With the Arctic getting warmer, the difference between the two regions is getting smaller and the jet stream appears to be weakening in lock step.

Weather isn’t climate, as exasperated climate scientists are quick to point out but, in the face of an extreme winter for many parts of Canada, people are quick to question.

“You can’t “see” climate change,” said David Phillips, senior climatologist with Environment Canada. “You have to understand that climate change moves very slowly but with wild swings. We are conditioned to the fact that what we think of as climate actually doesn’t occur any more. Weather is not what it used to be. We plan for weather based on normal but we don’t have normal any more. There’s a joker in the weather deck.”

Those wild swings could become more common in the future. We’ll need some good weather forecasting to keep up.