This is at least the 4th major monsoon entering the Owens Vally this year. This moring (Tuesday 8/27) clouds were forming below the Sierra peaks. This is usually reserved for after rain has occurred in the valley of the moisture has been around for a while. Very unusual. The dew points have but a little elevated the past few days with no real sign of clouds which is unusual as well.
Dew point is the best indicator of moisture in the air. Dew point is the temperature at which air becomes saturated. IF the air temp is 70 and the dew point is 70, its probably foggy. IF the temp is 70 and the dew point is 17, then its pretty darn dry.
Relative humidity, which is the most common indicator, goes up and down with the air temp. The higher the air temp, usually the low the relative humidity which explains why its called "relative" humidity, or just humidity.
Dew point doesn't care what the temperature is for the most part and stays rather constant, so its an easy to read indicator of the amount of water that is really in the air.
Todays monsoon is coming form the remnants of tropical storms in the eastern pacific along with the regular monsoon moisture that resides over Mexico (the meaning of monsoon comes from the movement of air from one place to another). Hope lightning storms accompany this latest surge of moisture.