San Juan Island prairie (top) and lavender farm (bottom)I just got back from giving some lectures in the San Juans and if any place has localized weather features...it is there. The complex combination of terrain and water caused large weather variations, as does the proximity to the Olympic and Vancouver Island rainshadows.
First, there are large variations in annual precipitation. The southern portions of San Juan Island and Lopez get around 20 inches a year due to their proximity to the Olympic rainshadow, while the northern SJuan Island (say northern Orcas) gets around 30 inches, with more on Mt. Constitution and the higher terrain. Lavender likes dry conditions, so there is no surprise that a large lavender farm is found on southern San Juan Island (Pelindaba lavender farm). With dry conditions, wind, and sandy soils, southern SJ Island even has natural prairies (see image above).
Wind variations are huge there. Blockage by the terrain causes "wind shadows" in their lee. Locations (such as Mt. Constitution on the NE side of the islands get hit by the strong wintertime northeasterlies exiting the Fraser River valley. While I was kayaking one morning on the eastern side of the Orcas I was struck by the strong wind accelerations near even modest points and headlands. During the wintertime, strong southeasterlies can buffet the islands (particularly the eastern portions)...winds that are accelerated by troughing (low pressure) to the lee (north) of the Olympics. In fact, when I hiked a bit on the top of Mt. Constitution (2500ft) I could see trees that had fallen in two directions...to the SE (from the Fraser flow) and to the NW (from the strong wintertime southeasterlies).
I found lots of well-educated weather enthusiasts on the San Juans and appreciated the invitation of the San Juan Nature Institute and the San Juan County Dept of Emergency Management . And two very nice book stores--Darvill's Books (Orcas) and Griffin Bay Books (Friday Harbor) graciously attended my lecture with my NW weather books. I left signed copies at both of them.
Editorial comment: Yesterday, I went to Lime Kiln park to view the Orcas...and was not disappointed. Viewed at least a dozen of these magnificent creatures. But I was shocked that both pleasure boaters and some fishing vessels ran just offshore revving their engines and making a terrible racket as they banged repeatedly into the water. Couldn't they stay offshore to allow the poor Orcas a chance? And then a helicopter came in low and circled over them, followed by a twin-engine aircraft that came in for a look. This cacaphony can't be good for the whales, can it? The whale watching boats were out their too....shadowing the orcas...but they seems a bit more discreet than the others.
