I noticed that in the PNW in USA and Canada, the rainy season is in the winter whereas the summers are relatively dry. However, move a bit inland to the interior of Washington/BC, and the rainy season becomes summer whereas the winters are fairly dry.
What causes the flip?
In: Earth Science
The Puget sound is a low spot between the high spots created by the Cascades and the Olympic peninsula. Is basically forms a bowl. Or at least a long wide valley.
The colder air gets the less water it can hold, the warmer it gets the more water it can hold.
Air is cooled going up mountains and heated coming down mountains because of the change in pressure.
In the winter the ocean and some extent the water in the sound is warmer than the air. This releases water into the air but it’s water the gator can be cold. As a consequence the water falls out of the air quickly and it rains here in the Puget sound area.
In the summer the air is hotter than the water. The air drinks up the water and is still warm enough to hold even more water. So it doesn’t rain anywhere near as much except on the coldest days.
Then the air blows up into the Cascades. Clouds form over the mountains and there is some rain. But the condensation of the water vapor into clouds actually heats the air. So blowing over the mountains does not completely dry the air.
But you’re still at a higher altitude so the air still can’t hold all the water because it’s continuing to cool.
As it cools more water rains out releasing more heat into the air as the water condenses which lets more of the water continue on farther east and so forth.
Once the cycle runs out and you start going down the eastern slopes of the Cascades you basically hit the high desert. Sometimes water gets there but not as much as you get in the mid cascade region which takes up most of Washington State.
So basically the terrain pumps warm moist air out of the Puget sound basin during the summer because the air is hot enough to hold the water long enough to escape the basin.
During the winter the air doesn’t quite get enough energy to hold on to the water for very long, so as the heat dissipates into space during winter the rain falls almost as soon as the clouds form and we end up getting winter rains in the basin.
Latest Answers