Recently, I learned that the eclipse can actually help reduce some types of clouds. As I listened to a second source discuss this, he mentioned (almost in passing) that if we have storm clouds, we should try to head for an area (in the path of totality) with a high pressure area.
What is it about regions of high pressure that can become our ally as we hope for clear skies during totality?
High-pressure domes bring clear skies low humidity and low rain chances.
The atmosphere is constantly mixing not just across the face of the planet, but also vertically. Where air is rising, you get low pressure areas, and where it’s falling you get high pressure.
Clouds depend on rising, humid air from the surface carrying that moisture up into the relatively cooler upper atmosphere, where the cooling water vapor condenses to forms the clouds. Where you have a high pressure area with air descending from the upper atmosphere, there is little opportunity for cloud formation. Not only is there no moist surface air being lofted there, the relatively dryer air from the upper atmosphere actually warms up as it descends via “adiabatic” heating, being compressed by more and more dense atmosphere. Warmer air can hold more water in vapor phase without reaching dew point, avoiding condensation and cloud formation.