Weather talk: Temp can be misleading 'in the sun'
It seems simple enough to hold a thermometer out in the sun in order to get the temperature “in the sun.” But that is wrong. Think about how hot the hood of a car gets in the sun. It can be blistering hot to the touch and obviously hotter than the air. You always have to measure air temperature in the shade. Air isn’t heated up very much by sunlight, anyway. The rays pass right through. Air warms up in sunlight mainly because the sun’s rays heat the ground and that heat then rises up into the air via conduction and convection. A thermometer bulb in the sun will heat up dramatically past the ambient air temperature because it is a solid object and is warmed directly by the sun’s rays. A thermometer in the sun is really just measuring the temperature of the thermometer bulb.