LCL is the height where air has cooled to the dew point. We can calculate LCL using temperature and dew point at the surface.

Like temperature dew point also decreases with height because of decreasing pressure. Dew point drops at the "dew Point Lapse Rate (DPLR) of 0.2 degrees C/100m (1.0 degrees C/500m)
What is the Air Temperature and Dew Point at the following heights?
Air Temp Dew Point
2000m,
1500 m,
1000 m,
500 m
surface 26 degree C 10 degrees C