If the temperature of air is lower than the dew point, water vapor condenses and leaves the air in the form of water. At this point relative humidity is essentially 100%. The dew seen of leaves in the morning is the result of atmospheric temperature falling below the prevailing dew point.

Forecasters watch the dew point, not relative humidity, because hot air can hold more moisture than cool air. At 90 degrees, we feel uncomfortable at dew points of 65-69 degrees. But the RH may be only 44 – 52 percent (half the atmosphere’s capacity). Dew points above 70 degrees feel oppressive.

Cold air does not hold as much water vapor as warm air, so the vapor (or gas) turns to a liquid and forms dew. That process is called condensation. Although the air temperature can never go lower than the dew point, the dew point can drop as the temperature goes down.

Relative humidity DO NOT need to reach 100% in order for condensation and rain to take place. As long as the actual temperature drops to below the dew point temperature with enough water vapor in the air, cloud formation and rain can occur.

Most of the time when it is raining the relative humidity is 90-99 percent, but not often is it 100 percent. Clouds form when invisible water vapor gas condenses into visible water droplets, and rain occurs when droplets grow too large to be supported in the air and they fall.

A dew point of 70 or above is really going to weigh you down and bump up the feels like temperature significantly. Comfort Scale. Warmer air is able to sustain higher levels of water vapor.

The dew point is actually proportional to the amount of water vapor in a given parcel of air, so that an increasing dew point means there is a greater concentration of water vapor molecules present and vice versa. So, for example, air with a dew point of 62 is more “moist” than air with a dew point of, say, 35.

The worst combination for human comfort is a high dewpoint (65 F or above) combined with a high RH. If the dewpoint is above 65, it will generally always feel uncomfortably humid outside. Dewpoint is related to the quantity of moisture in the air while relative humidity is related to how close the air is to saturation.

Morning condensation (dew) is very common in some regions and can easily be forecasted. The favorable weather elements for dew include clear skies, light wind, decent soil moisture, and low night-time dewpoint depressions. Dew forms when the temperature becomes equal to the dewpoint.

According to the Environmental Protection Agency, the best indoor relative humidity falls between 30% and 50%, and it should never exceed 60%. Other studies suggest 40% to 60% is a better range.