October 24, 2019

Puget Sound's Autumn Colors are the Best In Years. But Why?

Fall is my favorite season.  

The crispness of the air, the smells, warm apply cider, the return of storms, and the fall colors.

And it seems to me that the colors around Puget Sound this autumn have been the best in years.  Lots of bright yellows and, most importantly, vivid reds (see some samples below).  I admit that this is my subjective evaluation, but people I have talked to agree.

But why have the colors been so good this year?  Is there a meteorological explanation?

Seattle's Japanese Garden on Oct 19th taken by J. Sathish

Since I am not an expert in tree physiology, I checked with an authoritative source:  the U.S. National Arboretum.   Here is what I found.  According the National Arboretum the best fall colors are associated with a  moist growing season followed by a dry autumn period with sunny days and cool, frostless nights.

Late summer and fall drought is bad, since it can trigger an early shutdown of the trees, resulting in premature leaf fall.   The leaves never achieve their full color potential.

Frost is bad, leading to poor fall color and early separation from the trees.

So let's check out this summer, using Seattle Tacoma Airport weather observations.

First, let's examine the temperatures since June 1, with the average highs (purple) and lows (cyan), shown for reference.  We had a warm summer with lots of sun.  Then in September we had chilly mornings but with no frost.   Very good.
Precipitation?  Here is the cumulative precipitation since June 1st with both the observed values (purple line) and normal (cyan).    Summer was very close to normal, allowing us to escape the drought conditions that stress trees and produce early loss of leaves.  And the middle September period was wetter than normal, discouraging early leaf loss and allowing the colors to deepen and intensify.  Then we had a dry, cool, relatively sunny period in early October--just perfect to let the colors get even better.
Sunshine?  We had plenty this summer and particularly in late September and the first half of October (but not so much the last few days!).   All good.

Truly excellent weather conditions in all ways to get good color.

Last fall was disappointing with early leaf loss.  Not much reds.  But that made sense.  For example, as shown below, the precipitation was well below normal for the June 1- October 23rd period.  Leaves fell off early, turning a sickly yellow/brown with few reds.

The bottom line:  we had just the right weather this summer/fall to optimize fall colors.

 And it is not too late to enjoy it.  The Burke Gilman trail has splendid yellows, the UW Arboretum has wonderful reds, and great colors are found throughout western Washington.  So try to enjoy them...and then heat up some apple cider and be thankful you live in a place of such great autumn beauty.

Picture courtesy of Caroline Mass

The scene Wednesday morning as yours truly was biking in to work.  Doesn't get much better than this!


I will be giving a talk at 9 AM on Saturday at Portland's Oregon Museum of Science and Industry (OMSI) on the meteorology of the BLOB and westside wildfires.  The meeting is of the Portland Chapter of the American Meteorological Society and is open to all.  More information is here: https://oregonams.wordpress.com/2019/10/21/27th-annual-winter-weather-forecast-conference/


  1. Global warming will end fall colors in Seattle. Summer drought will result in all leaves falling off the trees by the end of September. Join 350.orgSeattle and take the fight to the oil companies.

    1. Or better yet don't contribiute to the proablem making things worse and read this instead https://cliffmass.blogspot.com/2019/10/the-real-climate-debate.html

    2. Ah yes, this remark illustrates how to spot of a con game—all their arguments are one sided. "Global warming," which morphed into a meaningless "climate change" when the warming trend fizzled, is always portrayed as creating negative results, here "end fall colors in Seattle." Life is not like that. Change comes with good results as well as bad.

  2. Northern California to Canada best Fall colors in years. Appreciate the insight for this explosion of color.

  3. Fall is definitely my favorite season too. I noticed the brilliant colors and other I know people did as well. I was wondering about it, so thanks for this article.

  4. Thanks for the information and pics. This really is a gorgeous and colorful fall, even in the mountains where conditions were far less warm and dry this summer.

  5. Thanks for this, Cliff. Always wondered about this correlation, specifically.

  6. The alpine larches in the North Cascades were *popping* this year. There's snow in the montane/subalpine forests now, but you can see these golden trees from SR 20 at the Washington Pass hairpin.

  7. The Bow, WA Rock-on-a-string weather reporting station hangs next to a katsura tree with now beautiful gold and reddish leaves and the smell of roasting marshmallows or some say cotton candy! The best of Fall ...

  8. Bellingham. Fall colors about the same as always.

  9. The colors were beautiful from the air yesterday on an arriving Alaska flight!

    1. I noticed that too! I was flying in Wed Oct 23rd on a southwest flight too and noticed all the reds and thought that was a lot of Japanese Maples, but now I'm thinking they weren't rows and rows of Japanese Maple trees but instead, just normal trees changing colors. It was beautiful.

  10. Beautiful photos, Cliff!

    We need only walk outside to experience similar beauty. It's a real opportunity to live in the moment and enjoy living in the northwest.

  11. Spent a few days in Wenatchee two weeks ago -- the colors coming/going over Stevens Pass were spectacular. Especially on the drive back west after it had snowed the night before. There was a white dusting on the trees/hills/mountains, blue sky plus brilliant autumn hues. Fortunately, no snow on the road, and being a weekday -- zero traffic. Sublime!

  12. Definitely the best fall colors I remember in WA. I keep being amazed that they leaves are not pummeled off by each wind/rain event too. Beautiful colors *and* staying power, it's great!


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