Rain Shadows around the World

I found this exchange about how unique the Olympic Rain Shadow is to be intriguing; we welcome any comments about other rain shadows around the world.

On Mon, Dec 6, 2010 at 5:30 PM, dick wilhelm <dick_d_wilhelm@yahoo.com> wrote:


I came across your site thanks to an article in today’s Peninsula Daily News (front page no less).  Will be checking it regularly for weather info and discussions.

My wife and I relocated in “the rain shadow” about eight years ago after retiring.  The Port Angeles/Sequim area seemed like a desirable place to live and we have not been disappointed.

One thing that has intrigued me since moving here, though, has been the focus on the rain shadow as if it were something unique.  It seems to me that it much resembles the climate differences seen between the eastern slopes and the western slopes of the Cascades, the Rockies and most mountain ranges in the northern hemisphere where the prevailing winds are west to east.

As the windward air climbs the mountains it becomes less dense and adiabatic cooling occurs at a fairly fixed rate.  Eventually the air cools to the dew point and condensation occurs.  Condensation heats the air thus slowing the cooling so that once over the top, the air is actually warmer than it would be otherwise.  On the way down the other side, adiabatic heating is the rule plus maybe a little heat from condensation in the higher places.  The result is that the leeward side valley basks in net warmer air than the windward side.  Warmer air holds more moisture and results in fewer clouds, thus the “blue hole.”  That warmer air is then cooled by the Sound so that it can rain on Seattle’s parade where it is supposed to.

Dick Wilhelm

From: David Britton [mailto:olympicrainshadow@gmail.com]

Thanks so much Dick;

I like your analysis of the adiabatic effect. there is alot going on there from a thermodynamics perspective.

You’re so right, there are alot of rainshadows…, east of cascades, east of sierras, central Spain vs NW Spain and France, they are all over the place.

But since the Olympics are a bit unique (clump of mtns rather than range), and situated as they are with the Puget Sound leeward, the rainshadow in the Olympics falls over an awful lot of water and waterfront. Haven’t found too many like that. Of course there is the sunshine coast in East Vancouver Island. Need to research that!


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