An old joke is told in places where it rains much of the time:
 
“Summer has arrived (in Seattle/ Vancouver/ Ireland/ Scotland/ Wales/ England) when the rain is warm.”
 
“You can tell when it’s summer in England, because the rain is warm” was cited in print in 1995. “If the rain is warm, it’s summer” was cited in 1995 and said about Vancouver. “How can you tell it’s summer in Seattle?  The rain is warm” was cited in 1996. It’s not known where the joke first started.
 
 
Google Groups: rec.travel.usa-canada
Need Vancouver weather forecast
SKing
5/11/95
(...)
LOL! You can also tell the season by the rain. if the rain is warm, it’s summer. If it’s cold, it’s winter!
 
29 December 1995, Mountain Democrat (Placerville, CA), “Gardening Books” by Carol Stocker (The Boston Globe), pg. C-4:
Elliott tries to explain Charles Darwin’s obsession with earthworms, the curious phenomenon of the “ha-ha,” the pastime of visiting British gardens, the 18th-century landscape designer who recommended fake volcanoes, and. of course. English weather: “You can tell when it’s summer in England, because the rain is warm.”
(The Transplanted Gardener by Charles Elliott.—ed.)
 
Google Groups: rec.humor
I need Seattle jokes
Bryan Porter
6/19/96
(...)
How can you tell it’s summer in Seattle?  The rain is warm.
 
Google Groups: rec.arts.disney.parks
A Ques. for you “over there”
Roy Johnson
5/10/01
(...)
Oh, and the final thing,the weather….in the UK it is damp all year round (been nice the last few days though!) . I think the only way you can tell it’s summer here is that the rain is warm 😉
   
allnurses
Mar 5, ‘06 by PNW_RN
(...)
How can you tell when it’s summer in Seattle? The rain is warm.
 
Google Books
Golf On The Edge:
Golfing around Britain’s coastal links
By Stephen Cartmell
London: Bantam
2008
Pg. 121:
There’s an old joke (but perhaps worth repetition) that you know when summer has arrived in Scotland because the rain is warm.
   
Twitter     
Candice Cossel
‏@SerendipityCand
My online research said “NY in the summer is hot. Even the rain is warm. Don’t bring a coat.” it’s 66 degrees… #fb
8:28 AM - 24 Jun 2011
 
Life Without Lemons
MONDAY
15 OCTOBER 2012
DANDRUFF FROM THE SKY
Somebody on Facebook wrote what is now the title of this post. 
It got me thinking…..............
Many see winter as a nuisance or an inconvenience. In the UK the only difference between the seasons is the rain is warm in the summer and cold in the winter.
 
Facebook
Charis Easter How do u know its summer in Wales? The rain is warm
February 4, 2013 at 3:02pm
 
Twitter
Eujobsite.com
‏@eujobsite
In Belgium, you know it’s summer when the rain is warm! pic.twitter.com/J6SS9fcb1k
5:22 AM - 22 Jun 2013
 
Rush Hour Rant
Posted by Ves on 09/02/2014 (February 9, 2014)
The Rant Has A Go At The Winter Olympics
(...)
How do you know its summer in Ireland? The rain is warm.