Thursday August 21, 2014





Break out the foghorns

Airport reports challenges from valley cloud, freezing rain as mild weather forecast to continue
Murray Mitchell

Grayson Vandepeear, 5, finds hockey to be easier on his knees as he gets a shot away on a foggy ice surface in Pine Valley. At right is his brother, Brett, 8.

If you prefer winters grey and mild, Environment Canada has some good news coming our way.

Compared to the rest of Canada and parts of the U.S., winter has been a gentle ride in the B.C. Interior so far, and that’s forecast to continue.

In short, expect more valley fog.

“Anecdotally, we think it has been a little bit worse than it has been in years past,” said Fred Legace, airport manager.

His colleague in Fort St. John, by comparison, had not a single snow-free day in December.

“They’ve had a tough winter,” Legace said. “We’ve had a tough winter on the other end of the extreme with fog forming.”

The prevailing weather is caused by warm Pacific air flowing into the snow-covered Interior, forming fog that is trapped by thermal inversions. Cloud cover becomes stratified, so the inversion ceiling can be as high as 500 metres.

It may have seemed as though every day in December was foggy and relatively warm, but conditions weren’t too far off the norm, said meteorologist Doug Lundquist.

“We usually do have that inversion in the southern Interior, but it was just so persistent,” he said.

Temperature-wise, the average in December was -4.4 C, about a degree cooler than the average. Aside from a cold spell at the beginning of the month, conditions were generally mild with intermittent snowfall and freezing rain.

That was due to a high-pressure ridge hanging over the province for much of the month of December, creating what’s sometimes called a “strata stack.”

Low-lying valley cloud tended to trap cooler air in the Kamloops area, while Kelowna was sunnier than usual, Lundquist said. That may have resulted from the fact that there is less snow cover in the Okanagan, so the ground absorbs more solar radiation instead of reflecting it, he speculated.

“What did stand out for me was that the central Interior was warmer on average than the southern Interior, which was colder than average,” Lundquist said.

Despite abundant fog, Kamloops Airport remained fully operational except for one day when flights had to be cancelled. Pilots can navigate by instruments through storms, but can’t navigate through fog concealing runway lights.

And if it wasn’t fog, it was freezing rain.

“We’ve had our share of issues, trying to keep runways and taxi-ways free of ice. It has been a challenge. We think it’s a bit unusual.”

Last year, the airport spent $80,000 on new de-icing equipment, which has paid off by reducing the treatment time from 12-15 hours to just 20-40 minutes. The de-icing chemicals in use now reduce corrosion of aluminum aircraft parts.

A westerly Pacific flow is forecast to dominate in the coming week, so even though a slight drop in temperatures is expected — a low of -7 C in Kamloops by Monday — it won’t come even close to the deep freeze back East.

“We may even see it become warmer by the end of next week. There’s not much winter coming,” he said.

Those who prefer real Canadian winter weather will find pockets at higher elevations.


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