Have you ever noticed a change in temperature just before, during, or after it rains? More than likely, it was a cooler change. This is especially felt with thunderstorms. On average, thunderstorms help cool the air by 10 to 15 degrees but temperature drops of as much as 30 degrees or more are also possible! This change in temperature can happen in a matter of minutes to an hour.
This cooling happens because of the rainfall which typically causes temperatures to drop. Just like any other meteorological phenomenon, there is a process to this and it is called evaporative cooling.
When rain falls into dry air, this causes the dew point to rise and the temperature to fall. The dew point rises because more moisture is being added to the air as the rain evaporates. During evaporation, heat is required (or absorbed) which is taken from the environment. When heat is removed, this is what cools the air and lowers the temperature.
Evaporative cooling can also turn a cold rain into wintry weather. Once the rain reaches the surface and evaporates, it further cools the environment to the point of potentially dropping below freezing. This can lead to icy roads.
This is why we need to be cautious on the roads whenever it is raining and temperatures are only a few degrees above freezing.
-Meteorologist Ronelle Williams