Shifting winds hard to forecast

Wind, according to KREM-2 meteorologist Tom Sherry, “can make a good day bad, and a bad day worse.”

Once it starts blowing at more than about 10 mph, it starts to impact people. Who wants to see the contents of their neighbors’ recycling bins in their yard on garbage collection day because it was windy the previous night?

Wind forecasting for the Spokane and Coeur d’Alene area is often a challenge. While temperatures from the Spokane airport on the west side of the city eastward into Coeur d’Alene may vary by about 5 degrees or so, such minor differences in temperature would not affect most people. Wind on the other hand, may be strong in Spokane, calm in the Valley, and light in Coeur d’Alene, or vice versa. These differences can be significant. Unfortunately, even giving each city its own wind forecast would not be able to cover all the variability of the region.

The prevailing wind direction for both Spokane and Coeur d’Alene during the spring and summer is southwest (meaning wind blowing from southwest to northeast). During the fall and winter, the southwest wind is still prevalent, but northeast winds are a close second. Wind direction also often follows a diurnal cycle in this area, with southeast winds during the overnight hours shifting to the southwest during the day and then back to southeast again.

So many factors, however, influence both wind speed and direction. The reason air moves at all is due to differences in air pressure. In general, air moves from areas of higher pressure, to areas of lower pressure. Beyond that, other factors come into play.

Wind cannot pass through solid objects, so it must either go up and over or around them. In mountainous terrain, wind can be funneled through narrow passages. Due to the conservation of mass, the air speeds up through such passages. A great example of this is the way northeast winds are funneled between the Selkirks and the Cabinet mountains. Folks in the Coeur d’Alene area, along with cities like Liberty Lake, get pestered by 15-25 mph northeast winds with significantly decreasing wind speeds as the terrain flattens out into Spokane.

Friction also impacts the wind. As you increase your elevation above the ground, wind speeds will increase. That is why a mildly breezy day in the valleys can evolve into chair lift closing conditions on the mountaintops. In a similar fashion, the Spokane Valley (at least at Felts Field where the observations are taken), will often show much calmer wind speeds than up on the exposed plateau where the Geiger Field weather station is located.

The presence of rain showers often creates high variability in the wind speed and direction. Stronger gusts can occur as rain-cooled air sinks and spreads out ahead of the precipitation.

The passage of a cold front will also result in not only a wind direction change, but an increase in wind speed as well. If a cold front is slowly moving west to east, folks in Spokane will start to suffer the effects of gusty southwest winds behind the front long before they are seen in Coeur d’Alene.

Overall, in response to my wind forecast inquiry in last week’s column, folks said that the wind forecast was just as important – if not more important – than finding out whether it would be cloudy or sunny, or wet or dry.