Complex sentence: On Sunday, 18 March 1945, the lower cloud ceiling at Kaltenkirchen was less than and most of the time between, while the upper cloud ceiling was at, rendering flight conditions outside the official operational specification for the Me 262.
Split into simpler sentences: On Sunday, 18 March 1945, the lower cloud ceiling at Kaltenkirchen was less than and most of the time between, while the upper cloud ceiling was at. The flight conditions were outside the official operational specification for the Me 262.