Weather radar can detect rain or snow and-most importantly-thunderstorms in the flight path ahead of the aircraft. Areas with rough weather are visible on a TV-screen on the flight deck and thus be avoided.
An Instrument Landing System (ILS) is installed at most airports. The ground station transmits a radio beam down the landing runway. An LIS receiver in the aircraft can guide the pilot- or autopilot- to follow the beam for landing in bad weather.