Humidity – it can make us feel hotter in the heat of the day, but it can also play a role in afternoon storms…
The dewpoint is a measure of how much moisture is in the air. The higher the dewpoint, the higher amount of water vapor there is in the atmosphere.
In the summer, many of our t-storms are slow moving. So, when storms develop, they’re able to take advantage of that moisture – and produce heavy rainfall rates . Sometimes those rainfall rates can be 1-3″ per hour! Combined with the slow moving nature of the storms, that amount of heavy rain can lead to excessive runoff and flooding of low lying, poor drainage areas.
Why do some storms move slow? Well, that’s determined by the wind speed in the upper levels of the atmosphere, thousands of feet up. If we have weak winds, the storms will move slower – leading to a higher risk of flooding. If we have faster winds, the storms will move much quicker, leading to a reduced risk of flooding rains.
The summertime is when the winds aloft are often weaker, so that’s why we often see more flooding events in the summer – combined with the higher humidity.