Cloud base (LCL)

Look at any puffy cumulus cloud and you'll notice its bottom is strangely flat — and every cloud nearby has its flat bottom at the same height. That height is the LCL, the lifted condensation level: the altitude where rising air cools enough for its invisible moisture to condense into droplets.

>A thermometer trick

You can estimate it yourself. Take the temperature (T) and the dew point (Td) — the temperature at which dew would form. The cloud base sits roughly

125 metres for every 1 °C of the T−Td spread.

Dry summer afternoon, T 30 °C and Td 10 °C? Spread 20 → cloud base ~2500 m, high and ragged. Humid pre-storm evening, T 24 °C and Td 20 °C? Spread 4 → clouds pressing down at ~500 m.

>Why tornadoes love low cloud bases

A tornado has to build an unbroken rotating column from the cloud down to the ground. The lower the base, the shorter the reach — and, just as important, the moister the air below the cloud. Dry air under a high base chills the storm's downdraft (evaporating rain steals heat), and that cold outflow cuts off the rotation before it can tighten. This is why the outlook's Moisture meter treats a base under ~800 m as a tornado ingredient, while a base above ~1500 m mostly rules them out — whatever the other meters say.