It is simply unnatural.
Contrary to local weather wisdom. Contrary to the normal state of things.
But it is true.
On some days, east of the Cascades is much wetter than west of Washington and Oregon.
Consider the total rainfall over the past three days (see below). More rainfall is reported east of the Cascades and only some rainfall in western Oregon and Washington.
Most of the rainfall in eastern Oregon and Washington is the result of convection – thunderstorms. To prove this, here are the lightning strikes on Wednesday and Friday.
Day after day, fairly violent thunderstorms developed on the eastern Washington plateau and along the eastern slopes of the Cascades. To illustrate, Mragain the radar image from 5:30pm today (Saturday), with red indicating very heavy rain.
OH. Lots of severe thunderstorm activity east of the Cascades.
Why is there so much wet action east of the Cascades, while western Washington is dry?
Good question.
As illustrated by the higher level map for Wednesday at 8pm, we had a low pressure/weak elevation band covering us. This feature steers clear of approaching storms and Pacific fronts, providing protection against rain west of Washington. This pattern also results in weak onshore currents, which bring cooler sea air into the lowlands west of the Cascade Peak.
Such low-level cool air is not good for creating instability and thunderstorms. As a result, western Oregon and Washington have few boomers.
But east of Washington and Oregon, there are Cascades to block the problematic cool air, leaving the door open for thunderstorms. Low-level warming is aided by high pressure, which enables large temperature variations with altitude—good for thunderstorms. And the warming of the surface by the sun is very strong now–helpful for thunderstorm formation as well.
Models predicting rainfall tomorrow show more of the same for eastern Washington and Oregon. Western Washington will be cooler and more cloudy on Sunday as the cool ocean air currents pick up.
Ultimately, all this rainfall east of the Cascades, plus the melting of an abundant Cascades ice sheet (thanks to the cool springs) led to a surprisingly rapid increase in reservoirs. supplies water to the Yakima River system (see below). Water prospects are good for agriculture.
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Interested in a free lecture at UW on How will we prevent fossil fuels from causing global warming by Professor Myles Allen of the University of Oxford? It will take place at 7pm on May 25 at UW’s Kane Hall, and you can get more information and sign up below. Professor Allen is a very good and internationally renowned speaker; Talk will probably fill up quickly, so book early if you want to go.
Professor Myles Allen will speak at Kane Hall on Thursday. His talk is also available online, but you must register in live or virtual mode.
