Wx radar is just like your TV - it has an on/off switch!
And no, even if 'on' as others have said it'd only see clutter on the ground, unless tilted 'up' when it obviously wouldn't see anything on the ground anyway. It's not a suveillance radar and isn't designed to detect aircraft, especially at close range. That's what TCAS is for! (Or preferably, ATC).
It's specified to show (unsurprisingly)..... weather sytems! And some obvious ground features like coastlines if tilted down when airborne.