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Is Port Angeles in the Olympic Rain Shadow?


That is an interesting question, and one whose answer certainly has a major impact on the weather in Port Angeles. To answer this we need to look at how much rainfall and sunshine Port Angeles receives and compare that to locations we know are in the rain shadow and locations we know are not. It is also important to look at seasonality, as the rain shadow typically forms during the winter and spring months.


In terms of precipitation, Port Angeles receives 25.57” of precipitation on average, compared to 35.86” in Seattle , and 16.51” in Sequim.1 Despite the large difference in precipitation, our sunshine results surprised us, indicating that Port Angeles has a climate that is quite similar to Sequim’s, is dramatically brighter than Seattle’s, and is definitely in the Olympic Rain Shadow! Here are the annual sunshine totals. 2
 

 

Annual Totals: October 2010-September 2011

 

 

The table above shows that during the study period, Port Angeles exceeded Seattle in number of bright sunny days by 45 % (128 vs. 88), and had 21 % fewer cloudy or dreary days (126 vs. 160). In terms of total recorded solar insolation, Port Angeles exceeded Seattle by 12%. Clearly Port Angeles is dramatically brighter than Seattle and on an annual basis has nearly the same sunny days as Sequim. For a better understanding of the situation, let’s look at some seasonal totals.

 

During the winter months, Port Angeles recorded more than 4X the bright sunny days of Seattle (16 vs 4), and fewer total cloudy and dreary days (48 vs. 53). However Sequim had more bright sunny days than Port Angeles, and dramatically fewer really dark and dreary days.


During the spring months, Port Angeles and Sequim recorded a very similar number of days with at least partial sunshine, and similar numbers of cloudy days, with the primary difference being more bright sunny days for Sequim.


However, in the brightest months of the year, Port Angeles took the lead with more bright sunny days (55 vs. 43). The difference in summer sunny days is likely due to the relative absence of maritime fog at the slightly higher elevation location of the sensor in Port Angeles.


Port Angeles’ similarity to Sequim’s sunshine profile and its dramatic differences from Seattle’s, especially in Winter, place it clearly in the Olympic Rain Shadow.

 

We also have archived monthly rain shadow climate summaries and individual monthly reports with daily sunshine charts and radiation plots, which look at Port Angeles conditions in more detail.

See our Rain Shadow Annual Days of Sunshine Report to view a summary of Sequim vs. Seattle sunshine, with more detailed analysis, links to monthly reports, and and study methodologies.

1 Precipitation data from the Western Regional Climate Center, http://www.wrcc.dri.edu/

2 This study is only over the one year where radiation data is available, but since we are most interested in the relative sunshine, not the absolute sunshine, we are not overly concerned whether 2011 was an especially wet year. In fact in some regards, the wetter the year, the better the year for studying the rain shadow, since it only forms during stormy periods. Still, though as more data becomes available, we will continue to track things.

 



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