Let’s start with a brief introduction to land and sea breezes. The uneven heating of water causes small scale coastal winds. During the day, the land heats up more quickly than the water and the air above the land creates a small area of low pressure. The air over the water remains cooler, so a small area of high pressure exists over the water. Winds like to blow toward an area of low pressure, so we see the wind blowing toward the coast or onshore and we call this the sea breeze or lake breeze. Usually the breezes are strongest right at the shore and diminish further inland. At night, the land cools more quickly than the water and the opposite happens and we get what we call a land breeze or offshore flow.
The leading edge of the sea breeze is called the sea breeze front. The temperatures behind the sea breeze front can be up to 10 degrees cooler than ahead of it during the first few hours. Cities along the coast usually experience the sea breeze by noon, thus cities along the coast experience their high temperatures earlier than inland cities. Where the sea breeze front meets the drier, hotter inland air, the warmer, lighter air will converge and rise and develop thunderstorms. This is why we so frequently have a 20 to 30 percent chance of rain on any given Summer day due to the sea breeze.
For those residents of mountainous regions, their weather is affected by mountain and valley breezes. During the day, the sun heats the walls of a valley and that warm air begins to rise up the side of the mountains, thus this is known as a valley breeze. At night, the wind reverses and the air is cooler and more dense, thus it sinks. This is called a mountain breeze. This type of wind flow is best developed in clear Summer weather where the winds are light. When upslope winds (valley breezes) are fully developed and have enough moisture, they build cumulus clouds over the mountains and showers and even thunderstorms form during the early afternoon or the warmest part of the day. Hikers, climbers and those who live in the mountains know this very well.
Now that we’ve learned about some of the effects that natural features have on winds, on Thursday, we’ll take a look at some of the special wind types, due to these features across the U.S.