Stormy weather indicates a sudden fall in barometer reading.

Explanation:
- A barometer is a device used to measure atmospheric pressure. It helps in predicting weather changes and is particularly useful in determining whether the pressure is rising or falling.
- When the barometer reading falls, it indicates a decrease in atmospheric pressure. This drop in pressure is often associated with certain weather conditions.
- Stormy weather is characterized by a sudden and significant decrease in barometer reading. This is due to the formation of low-pressure systems, such as thunderstorms or cyclones, which are accompanied by strong winds, heavy rain, and turbulent weather conditions.
- Storms occur when warm air rises rapidly, creating an area of low pressure at the surface. As a result, the barometer reading drops because the atmosphere above is less dense.
- The sudden fall in barometer reading is a clear indication that stormy weather is approaching. It serves as an early warning sign for people to take necessary precautions and prepare for the upcoming storm.
- On the other hand, calm weather, cold and dry weather, and hot and sunny weather are not typically associated with a sudden fall in barometer reading.
- Calm weather usually indicates stable atmospheric conditions with little or no change in pressure. Cold and dry weather often indicates high-pressure systems, where the barometer reading may be steady or rising. Similarly, hot and sunny weather can be associated with high-pressure systems, resulting in a stable or rising barometer reading.
- Therefore, out of the given options, stormy weather is the condition that indicates a sudden fall in barometer reading.