America's Rainiest City?

Ketchikan, Alaska is known for two things: salmon and rain.  I know this well as I have been here several times visiting family.  The combination of wind and rain often makes it feel like you are living in a car wash.

Ketchikan, which is located on the inland passage in southeast Alaska, has fully embraced it's status at the Rain City.  It proudly displays a "liquid sunshine gauge" on the boat dock showing just how wet it is.

A closeup shows that they claim an average rainfall of 12.5 ft (150") per year. 

 

That's a lot of rain and, perhaps not surprisingly, Ketchikan is widely promoted as the rainiest city in America (e.g., destimationalaska.com). 

Being a meteorologist, I began to wonder if this was really the case.  There are the usual challenges in evaluating such a claim.  What is meant by a city?  What is the period of record?  Is the data reliable?  Etc...

For the purposes of this post, we'll concentrate on climate stations for which there is data available on the Western Region Climate Center web site.  On that site, the Ketchikan coop site reports a mean annual precipitation of 153" with a period of record from Sep 1949 through Dec 2010.  So, the numbers quoted on their liquid sunshine gauge look good.

Incredibly, this is not the rainiest coop site in southeast Alaska.  That designation appears to belong to Little Port Walter, a NOAA research site on Baranof Island, with a mean annual precipitation of 229".  Unreal!  It is, however, not a city.

A quick pan through the coop stations turns of several that are quite wet.  Yakutat has a mean annual precipitation of 144" (Sep 1949 - Dec 2010).  Close, but not close enough.

Cordova is interesting.  There are two coop stations here, both with records back to at least 1955.  The Cordova North site reports an annual mean precipitation of 158", but with only 51% of the possible observations reported.  The Cordova Airport reports 90" with >99% data coverage.  What to believe?  

In the Pac NW, there do not appear to be any cities with a mean annual precipitation approaching that of Ketchikan.  Forks, WA, now famous because of the Twilight series, only averages 118".  

Then there is Hawaii.  Hilo appears to be the rainiest city, with a mean of about 127".  It rains far more than that not far from Hilo, but we're concerned here with the city.  Perhaps there is a small city in Hawaii that is wetter.  Students start digging...

There is one other wrinkle to throw at all this.  If one  goes to the "Monthly Station Normals of Temperature, Precipitation, and Heating and Cooling Degree Days 1971 − 2000," published by NCDC, Yakutat is listed with a mean annual precipitation of 160", Ketchikan only 137"!  Hmmm...

So, Ketchikan is certainly a rainy city.  Whether or not it is the rainiest likely requires more careful analysis of the available data, it's quality, and the potential influence of interannual and interdecadal variability on the mean for the study period.  All of this is a good lesson in the importance of metadata and data curation, as well as expert analysis and assessment.