Just as the equinox is occurring, an autumn temperature plunge is triggering sweater weather in the East. High temperatures drop by as much as 30 degrees this week, especially in places that have been dealing with relentless heat.

Watch the colors of the TemperatureRadar change from red-hot to cooler yellows and greens in the Mid-Atlantic and Southeast over the next four days. Cooler temperatures mixed with rain will have residents adding layers this week.

At the start of this week, a weak low-pressure system triggers unsettled, cooler weather for the Ohio Valley and Mid-Atlantic, but by the last half of the week, strengthening low pressure off the East Coast causes a cold-air damming effect. The cold-air damming keeps a cooler air mass locked between the Atlantic and the eastern slopes of the Appalachians.