When the wet bulb reading is very close to the dry bulb reading, what does this indicate?

When the wet bulb reading is very close to the dry bulb reading, it indicates that the air is holding a significant amount of moisture, resulting in high relative humidity. The wet bulb temperature measures the cooling effect of evaporation, and when it is close to the dry bulb temperature (which represents the actual air temperature), it shows that the moisture in the air is preventing much cooling through evaporation. Therefore, the higher the humidity, the closer these two readings will be.

In dry air conditions, the wet bulb temperature would be much lower than the dry bulb temperature, indicating lower humidity levels. Thus, the proximity of the wet bulb to the dry bulb reading is a clear signal of high relative humidity in the atmosphere.