World and Nation

Wind and Weather

Wind and Weather

Wind is an important parameter in determining the weather. Not only is the wind strength a factor (as it turns out, Boston is the windiest major city in America), but so is the wind direction. As you might expect, when the wind blows from the north or south, the temperature becomes colder or warmer, respectively.

But because of Boston’s position next to the ocean, whether the wind is blowing from the east or west makes a big difference. In the summer, the ocean is colder than the land, because it takes a lot more energy from the sun to heat the ocean. So when the wind blows from the east, it passes over the cool ocean, and makes coastal areas much cooler. In the winter, the reverse occurs — the ocean is warmer than the land, and a wind from the east makes the land warmer.

Sometimes it is large weather systems (the fronts, H’s, and L’s on the weather map) that make the wind blow in a given direction. In times of weak forcing between weather systems, a “sea breeze” flow may develop, particularly in the summer. During the daytime, the air over land heats up much more quickly than the air over the ocean. The layers of the atmosphere near the surface over the land expand, which lowers the air pressure near the surface. Because of this pressure gradient, air flows from the ocean to the land. This flow usually penetrates only a few miles inland, so downtown Boston and Logan Airport (where official weather measurements are taken) will be cooler than MIT’s campus, which is cooler still than more distant parts of Cambridge. So as you are enjoying the pleasantly cool temperatures today (and yesterday), thank the sea breeze.

Extended Forecast

Tonight: Clear. Low 62°F (17°C).

Tomorrow: Mostly sunny. High 84°F (29°C).

Tomorrow night: Partly cloudy. Low 66°F (19°C).

Thursday: Partly sunny. High 84°F (29°C).