When the dew point temperature is close to the temperature of the air, the air is nearly saturated. However, nearly saturated air is not always humid. Humidity of the air generally increases southward, similarly to the temperatures. In the example above on the left, there is a large change in dew point temperature from New Mexico to central Texas. This suggests that a dry line is somewhere in the area.
Humidity decreases the convective stability of the air.
Since the density of moist air is lower it tends to rise over colder, denser air . This can happen along a frontal boundary or if air becomes convectively unstable and rises to form clouds and precipitation. This is why thunderstorms and convective showers often form in a warm, moist airmass. During the warm season intense precipitation often occurs along those boundaries. Temperature Maps Terms for using data resources.