Rain is liquid precipitation reaching the ground. Its beginning, ending and variability help distinguish mainly stratiform precipitation from convective weather.
A shower has an abrupt start and end with rapid intensity changes. A thunderstorm is present when electrical activity produces lightning and thunder, usually from Cumulonimbus cloud.
Steady or stratiform rain
Extensive cloud such as Nimbostratus can produce relatively uniform rain for many hours. Intensity may be light or heavy but usually changes more smoothly than in a shower.
Long duration increases the total and may saturate soil even without exceptional hourly rates.
Showers and thunderstorms
Showers come from vertically developed clouds and are local. One place may receive intense rain while a nearby area stays almost dry.
Thunderstorms add lightning and often gusts, hail or very low visibility. A storm does not need a large total rainfall amount to be dangerous.
Probability and amount
A 70% rain probability does not mean rain for 70% of the day or 70% intensity. It expresses the chance of measurable precipitation at the specified point and period.
For a fuller picture, read probability, expected millimetres, hourly rate, thunderstorm signal and location uncertainty together.
These explanations and calculations are educational. For safety, occupational, health, marine or aviation decisions, follow the appropriate official services.