The lower river is flow ice right now, but this is normal and is usually gone by February. Big Pines, down in the lower canyon, is the access area most affected. Try walking in/floating the upper river between S. Cle Elum and East Cle Elum WDFW access areas, although the East access can be very tricky in snow. So can the access area at Fireman's Park, so use the rough launch at the Hanson Pond's area.
Winter rules - aim for the warmest parts of the day (usually 11-3pm) and think slow and low. Streamers on sinking lines - Scuplzilla's, Wooly Bugger's, and Leach patterns in black and olive/orange work well this time of year. If you're indicator nymph fishing, or swinging wet flies, try a black Hares Ear/Disco Midge combination. Small, black winter stones (think 12-14) are also effective sub-surface. Midge dries and even BWO's can be a wonderful winter event, so stock a few of those too.
You can follow my fishing reports at www.orvis.com/derekyoung too - I normally begin to guide and fish the Yakima regularly around mid-February, but the prediction of sun and temp's in the 40's gets my gears going and I typically sneak in a day or three in December and January - give it a shot!