Okay, I understand more clearly. You were wondering about weather in Twice Walla and the rest of the Columbia Valley appellations. And I’m sorry, but I can’t give you an answer for that.
Now . . . as for the rain . . . it’s true. Everything east of the Cascades is essentially a desert. The Willamette Valley runs between the Cascades and the Coast Range, roughly in a band ranging from 40-80 miles from the ocean. The 40 would be the eastern foothills of the Coast Range and the 80 would be the Cascade foothills.
That said, here in Portland we get about 35 inches of rain a year; a little less than what New York City gets but - because of the Coast Range - way less than the 80+ inches they get in places on the coast. Salem gets a similar amount, whereas Eugene gets about 50 inches. The Rogue/Applegate region is actually in a spot where the Siskiyous, the Coast Range and the Cascades collide, and it’s much, much warmer and - in the case of Medford - drier. Medford gets something like 15 inches of rain in a year whereas the Applegate region gets around 30. The valley floor is also around 1300 feet, which is higher than anything in the Willamette Valley proper.
The Umpqua region surrounds Roseburg and has rainfall similar to the rest of the Willamette Valley, but it IS considerably warmer during the growing season depending on elevation and microclimate. That’s why pinot noir and cabernet both ripen there.
Now . . . back to the Willamette. Ribbon Ridge, Chehalem Mountain, Dundee Hills, Yamhill-Carlton, McMinnville and Eola-Amity - in other words all the important pinot noir appellations - are actually on the western (not eastern) side of the valley, west of the river and I-5. In fact, portions of the Yamhill-Carlton and McMinnville AVAs extend into the lower foothills of the Coast Range. They’re also all within about a 15-mile radius of wherever the central point would be - probably somewhere around McMinnville. As a result, the weather doesn’t vary much with one exception - and that’s the Van Duzer corridor effect, which funnels cooler air from the ocean to the Eola-Amity and McMinnville AVAs. It’s not a LOT cooler, just a bit.
As for the Columbia, I don’t personally see any evidence that it funnels any rain past the Cascades. The wide mouth tends to add a bit of emphasis to the fact that the Willamette Valley is a maritime climate, but if one drives east past Hood River, which is at the northern foot of Mt. Hood, the landscape turns to desert almost immediately. In fact, the average rainfall drops in half - from 30 inches at Hood River to 14.5 at The Dalles - in a distance of 22 miles. The gorge is really narrow at Hood River which makes for great windsurfing, but I digress from weather. As far as I can tell, the primary weather purpose of the gorge is to funnel arctic air into Portland and give us ice storms.
Twice Walla, by comparison, gets 12 inches, though that IS marginally higher (in growing terms) than Richland/Kennewick/Yakima where they get about 8 or 9. I don’t know whether to attribute that to the fact that WW is a straight shot out of the end of the gorge where the Columbia turns north, or its proximity to the Blue Mountains on the east. I’m inclined to go with the latter. Either way, you can’t dry farm - or at least I don’t think you can.
So . . . I hope that helps. And yes, I live in Portland about a 40-minute drive from Jacki, so my weather reports are going to be similar to hers. Anything east of the Cascades will be different.