On the radar control panel before while your taixind sellect power on and it will automatically be on stand by. As you taxi on to the runway or are on the runway sellect wxa. On the EFIS turn on the weather button, it's right under the right nob, once it's on just leave it (no need to turn that off when shutting down). Once you are taxing off the runway after landing be sure to turn the Radar off though by pressing the power botton.

In case you don't know, the EFIS is beside the throttles and the radar panel is below them.