a useful tool while flying is any straight edge/ruler/checklist...look down the straight edge at the tops of the clouds, move your head back and look at the straight edge and see if it is pointed UP or down from level
At low speeds, weather can change faster than we fly. I've flown west from Inverness, in the morning, towards and above an unbroken cloud layer. It broke up completely as I flew over it. Cloud tops rise, and cloud layers form. CBs form and dissipate.