Purcell trench is source of strong wind gusts

March usually has the reputation for being the windy month, but it looks like our windiest weather held off until April.

In the first two weeks of the month, six days saw maximum wind gusts of over 30 mph. What direction do the strongest winds usually come from? When speaking of wind gusts, the sudden brief increase in wind speed, the strongest winds are usually out of the southwest or west. In Spokane, strong sustained winds are usually out of the southwest as well. From just east of the Spokane Valley into Coeur d’Alene, a strong sustained northeast wind can also become a nuisance, though I’ve rarely heard of a gusty northeast wind knocking out trees or causing damage.

The pesky strong northeast winds are a result of a funneling effect through the Purcell trench between the Selkirks and the Northern Rockies. This trench runs from about Bonners Ferry through Sandpoint, Coeur d’Alene, and then into the Spokane Valley. The effect is lost by the time you get to the Spokane weather observing station on the west end of the city at the airport. A similar wind funneling effect occurs in Ellensburg, but for winds from the northwest.

It is always fascinating to study topographic maps of the area, to see how the locations of the mountains and the river valleys influence elements of weather such as the wind. It is also fun to correlate the lay of the land to other weather factors such as precipitation amounts and even preferred locations for thunderstorm development.

Now that we’ve finally gotten a taste of some truly mild weather, I see trees budding and flowers blooming. Don’t forget, though, that the average date of the last frost is still about 2 1/2 weeks away. Overnight lows the last several days have been in the upper 30s and low 40s, but we did dip into the 20s back on April 10. Average highs are now in the upper 50s with average lows in the mid 30s. April showers have helped put April precipitation into the near average category, with .65 inches for Spokane and a healthy 1.30 inches for Coeur d’Alene as of the 14th. More rainfall is needed, however, to close the year to date deficit of about .75 inches in Spokane.