Weather topic #7

 

Windstorms

Windstorms are some of the most damaging weather scenarios we receive in the Pacific Northwest. Winds we typically receive in the Pacific Northwest are only high enough to be classified as “blustery”, but with the right conditions aloft, areas of the PNW can be hit by highly damaging wind speeds.

Wind is caused by a gradient in pressure. By “gradient in pressure” I mean a change from low to high pressure over an area. The tighter the gradient, the higher the wind speeds. PNW wind is caused by a low setting up off the coastline, and then moving over the area. The favorable trajectory for high winds is when the low sets up slightly to the north, because the pressure gradient is typically denser on the south side of the low. The SE corner of the low, (where it begins to curve north), has the highest winds, and these winds are known as Bent Back Occlusion winds. 

Wind can also be impacted by local terrain features. Some features can amplify the wind. One of these is the Columbia river gorge. As the low moves closer to land, air streams out of gaps in the mountains, like the gorge, because it is being pulled toward the low pressure center. This creates strong east winds in the foothills. Hills can also block many areas 

from receiving high winds if they are just upstream of where the area is.