Quote:
Originally Posted by Janet
I always thought the higher the humidity the warmer the lake temp. Is this a myth or am I correct in thinking this?
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It's not myth, and humidity does factor in. As the dew point of air climbs out of the 50s (nice and dry!) into the low 60s (noticeably humid), and into the 70s (downright muggy - tropical), the rate of evaporation of water at the lake surface is retarded significantly. Turning a lb of water from liquid to steam (humidity in the air) takes about 1,000 BTU/lb. That heat comes mostly from the water itself and tends to chill the water. So you have two effects working against each other. A hot day's air and direct exposure to the sun's rays tend to warm up the surface water, while evaporation from the surface tends to cool it.
When you climb out of the water on a humid day, evaporation of water from your skin is a lot slower than on a dry day, so you don't feel the cooling as much as on the dry day. Similarly, after a prolonged hot, humid spell, which has warmed up the surface water considerably, a Canadian front bringing in dry air on the breeze enhances evaporation, and the surface water is cooled notably in short order.
While having nice warm water may be pleasant for hanging around in the water, we shouldn't want too much of that, as warm water temperature tends to work against water quality and general health of the lake.