Cold air funnels not usually dangerous

In the previous article, we looked at how scientists believe tornadoes form and why they remain difficult to predict.

Fortunately, tornadoes are relatively uncommon across Canada, and not every funnel cloud beneath a thunderstorm becomes a tornado.

Canada has its own version of Tornado Alley, stretching from southern Alberta through Saskatchewan and into southern Manitoba.

Warm, humid air moving north from the United States frequently collides with cooler, drier air arriving from the Rockies and northern Canada.

Add strong winds higher in the atmosphere and you have some of the country’s best conditions for severe thunderstorms and tornadoes.

Canada records roughly 60 to 100 confirmed tornadoes a year, although the actual number is likely higher. Many weaker tornadoes occur over forests, farmland and other sparsely populated areas where they may go unnoticed.

The Prairie provinces account for a large percentage of Canada’s tornadoes, with southern Alberta and Saskatchewan seeing some of the highest numbers. Most Canadian tornadoes occur between June and August.

Our ability to forecast tornadoes has improved dramatically.

Doppler radar allows meteorologists to detect rotation within thunderstorms, while satellites monitor storm development.

Even with these advances, tornado forecasting remains a major challenge. Meteorologists can identify when conditions are favourable, but determining exactly which storm will produce a tornado and where it will occur is much more difficult.

Adding to the confusion is the fact that not every funnel cloud is associated with a severe thunderstorm.

Across the Prairies, we frequently see cold-air funnels. These usually develop beneath thundershowers associated with an upper-level low, where unusually cold air several kilometres above the ground creates enough instability for narrow updrafts to develop.

Another ingredient is vorticity, which simply means spinning air.

The atmosphere contains many small pockets of rotation, and if one becomes caught in a strong updraft, the rising air stretches the rotation vertically.

As it becomes narrower, it spins faster, much like a figure skater pulling in their arms. The result can be a narrow funnel cloud extending beneath the cloud base.

Cold-air funnels tend to be thin and rope-like and usually disappear within a few minutes. On the rare occasions that one does reach the surface, it technically becomes a tornado.

Because these tornadoes form without the rotating mesocyclone found in a supercell, they are often referred to as landspouts and they are generally weak.

Because there is always a possibility that a cold-air funnel could briefly touch down, Environment Canada will occasionally issue a special weather statement when conditions are favourable.

In most cases, simply keeping an eye on the sky and moving indoors if the funnel approaches are all that is required. Both are reminders of how complex our atmosphere can be.