So naturally I was curious when told that PNW Summers are nearly rainless and have vanishingly low humidity, while Texas is of course rainy and humid. Seems too pat with regard to my experience in gardening and while not scientific these links illustrate that seedlings of invasives experience actual weather not averages. Since weather in August is the most stressful (from my experience) I chose that month from Weather Underground (2010) for both cities both in USDA zone 8. Austin,TX. http://www.wunderground.com/weather...STI47&day=3&year=2010&month=8&graphspan=month Edmond, WA. http://www.wunderground.com/weather...C4429&day=3&year=2010&month=8&graphspan=month Note the humidities for both locations, I was surprised how close they were. The distribution of rain also surprised me, not only the amount by how it was distributed. Evenly spaced rainfall is most helpful to any plant trying to get established in a new area. What little rain we got in Texas was all evaporated within a day at the temperatures recorded in 2010. It would seem other factors besides rainfall, humidity play a part in plant establishment in these two climates.