On a hot day, temperatures outside in the sun can feel much hotter than the meteorologist reported, and on cold days, the sun's rays can help cut the icy chill. The temperature difference between shady and sunny areas depends on a number of environmental factors.
Range of Temperatures
It is impossible to predict an exact number of degrees by which the temperature will differ in the sun and the shade. An extreme example is a photograph of former USA Today weather editor Jack Williams in the sun next to a thermometer reading over 26.7 degrees Celsius when the actual air temperature was only 0-6.667 degrees Celsius.
Type of Thermometer
Temperature readings not only measure the air temperature, but also the temperature of the thermometer itself. If the thermometer is large and metal, the sun's rays will heat it significantly, elevating temperature readings in the sun.
Time of Year
The angle of the sun affects how much the sun will warm the objects it hits, and the temperature difference between sun and shade will likely be greater in the summer than in the winter.
Time of Day
Likewise, the difference in temperature may be more noticeable in the middle of the day when the sun is at its highest point in the sky.
The temperature difference between shade and sun is less obvious when it is windy because the wind brings air from the shade into the sun and vice versa.