Seattle
I can't think of a better place to do instrument training than the winter in Seattle. Unfortunately for instrument students, it's summer right now.
It's highly unpredictable in the summer in Seattle. Monday was gorgeous and sunny. Tuesday started out great, I flew over the eastern WA, then some serious t-storms in the west in the afternoon (I watched the radar on the internet from sunny Chelan). Wednesday was 85 and sunny in Chelan when I took off, but from Cle Elum west was solid IMC, rain, light turb the entire way home; perfect instrument flying weather, just what you are looking for. Freezing level was up around 110 so no ice threat where I was flying. But you just never know around here. I might have had to wait a day or two to fly home because the freezing level could have easily been down at 050 or so and I won't fly over the mountains if there's even a risk of ice...there's nowhere to descend except trees and rocks!
Having said that, July and August are typically sunny.
I did my instrument training October-Feb a couple winters ago. I got a ton of actual, mainly because the freezing level frequently sits above 030 even in the winter, and there are plenty of low altitude places to fly in the Puget Sound area. I did get in a couple of interesting ice experiences, as well, though; it's nice knowing that you're over the Puget Sound and the temp down there is well above freezing, especially as the clear ice starts rapidly building on your wings at 040 ("uh, Seattle approach, Cessna 12345 would like lower because the accumulating ice is going to make us go lower in about 20 seconds anyways!"),