The West Bar area is on the Columbia in the Colockum Wildlife area, which is one of several small wildlife units in the L.T. Murray wildlife area NE of Ellensburg.
These areas are closed until May 1st for wintering Elk and are generally passable after March. There might be some snow up at higher elevations (Colockum Pass) but I doubt it.
We did a long trip last year that involved leaving pavement in Ellensburg, camping out on the bar for 2 nights, then heading north into Wenatchee to resupply. After that, we headed east to some BLM land to meet up with some more cruiser guys near Douglas Creek for another night of camping and exploring, along with a bit of swimming.
If we're interested in more driving than camping, the Wenas area south of 90 (West of Yakima) is also a nice area, and we've got a favorite spot to camp for the night out there as well.
L.T. Murray Wildlife Area -
http://wdfw.wa.gov/lands/wildlife_areas/lt_murray/
Douglas Creek -
http://www.bentler.us/eastern-washington/recreation/douglas-creek.aspx
Many of the wildlife areas often have burn bans, which is something to consider for camping.
West Bar campsite: 47°12'49.42"N, 120° 0'28.42"W
Douglas Creek site: 47°27'46.77"N, 119°52'25.37"W
Pictures from West Bar: