In reply to bigdrew:
Please note that I'm extrapolating a bit here as I've only been there in late November-early December.
On this basis, best be prepared for it to be a bit on the cool side in January, especially on the north side of the range. If for any reason it's not, then that'll be a bonus. After all, Tafraoute is at about 1200m alt., so don't expect temperatures of >20C; 10C-15C may be more like it although it may feel a little warmer in the mid-day sun. Also, it may take a bit of time to warm up in the mornings and it'll definitely be very chilly at night. I think January is one of the drier months, so I wouldn't be too concerned about any rain.
If it is rather cool, then climbing on the granite could be the best/ warmest option although I think you should be fine on any south-facing crag.
When we were there, we mainly had settled blue skies and sunshine but there was quite a stiff breeze all the time, leading to some wind chill, which meant we were more often than not wearing two top-half layers during the day, usually a tee and a thin softshell or lightweight fleece. The locals said the wind and the temperatures we experienced were normal for the time of year. Out of the wind it felt quite warm.
HTH
Dave