Sabal is a genus of fan palms from the south-east USA, Mexico and the Caribbean. It is a rather interesting group of palms in that they are all extremely cold hardy (with a few exceptions) but they are not generally 'cool-tolerant' and will sulk without a lot of heat. It seems that average high temperatures in July and August must exceed about 23°C/75°F (as a very rough estimate) in order for them to grow well, but it also helps if year-round temperatures are mild such as in south-west Oregon. They can grow with marginal success in the Puget Sound area and points north, and would probably grow pretty well in the Willamette valley of Oregon.
There is some variation in cool-tolerance: the most cool tolerant species seem to be S. bermudiana, S. causiarum and S. domingiensis. These species originate in the Carribean, but seem to do at least as well here (including being quite winter-hardy) as those species native to the United States. S. 'riverside' shows good cool-tolerance but has not been consistently cold-hardy. Some forms of S. minor (which is variable) are also very cool tolerant. It remains to be seen whether S. palmetto, S. louisiana, S. 'birmingham', S. X texensis, S. texana, S. uresana, S. etonia, S. rosei, S. 'tamupilias' (or whatever), S. 'ferguson huge leaf' and other hardy species (did I forget any?) will perform as well. In any case they are all painfully slow in our cool climate. S. mauritiiformis and S. yapa, however, are quite frost tender and should probably not be tried.
Some Sabals ought to do well in eastern Washington, especially in milder areas. My top recommendations would be hardier populations of S. minor (such as those native to McCurtain County, Oklahoma), which is generally considered to be the next hardiest palm after Rhapidophyllum and would probably grow well in USDA zone 6, and S. 'birmingham' which just may be the hardiest palm with a trunk. S. uresana might also be worth a try, since it is native to desert areas, and is, in my opinion, the most beautiful species.
Sabals require a constant supply of water to grow well. Rich soil and regular fertilizing once established might also help to speed them up some.