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Boston Weather: 36.0°F | Partly Cloudy
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Dry Week Ahead

This week, an area of high pressure will dominate the eastern third of the country. This high pressure region is forecasted to move very slowly from west to east, which means we will see an extended period of dry weather. A low pressure system that might graze us Thursday night is the only chance we have for rain through Friday. Today will be sunny with perhaps a few fair weather cumulus clouds. Even though the sun will be shining, the wind will blow in cold air out of the north. On Wednesday and Thursday, the winds shift and come from the west, which will result in temperatures in the low to mid 60s. Evenings will still be chilly, since the lack of cloud cover lets thermal radiation escape easily into space.

Why does a high pressure system give us sunny, dry conditions? A balance between the Coriolis force and the pressure gradient force makes the air move clockwise around a high pressure center. Friction near the ground reduces the speed at which the air circulates, weakening the Coriolis force and giving the pressure gradient force a slight advantage. As the wind acquires a slight outward component, air from the middle is replaced by air sinking from the upper atmosphere. Sinking air is very stable, as opposed to rising air which can cause water to condense out and rain. Any clouds that might form from instabilities near the surface will be limited in their growth by the stable atmosphere above.

Extended Forecast

Today: Mostly sunny. High 53°F (12°C).

Tonight: Clear. Low 37°F (3°C).

Tomorrow and Thursday: Sunny. High 61–65°F (16–18°C). Low 43°F (6°C).

Friday: Chance of rain in the very early morning; otherwise partly sunny. High 67°F (19°C). Low 44°F (7°C).