Which condition demands a careful check of the dry-bulb reading?

The condition that warrants a careful check of the dry-bulb reading is the presence of frost. This is because frost formation can significantly alter the temperature measurements and indicate a change in the dew point, which is crucial for forecasting weather conditions.

When frost is present, it can insulate the thermometers, causing inaccurate readings of the air temperature. The dry-bulb thermometer measures the ambient air temperature, and if frost forms on the instrument, it might not accurately represent the temperature of the air around it. Thus, it is essential to check the dry-bulb reading carefully to ensure accurate observations and weather predictions.

In contrast, while extreme humidity, high wind conditions, and rain can affect weather conditions, they do not directly impact the accuracy of the dry-bulb temperature readings in the same way that frost does. Each of these conditions may necessitate attention for different meteorological reasons, but the correlation of frost with dry-bulb readings requires more precise checks to ensure that the measurements reflect actual atmospheric conditions.