Eclipse to send temperatures tumbling across U.S., meteorologists say

Getting ready to watch the solar eclipse? Bring a sweater along with those special glasses because the mercury could dip as the moon’s shadow crosses the land.

Millions of Americans across a 112-kilometre corridor from Oregon to South Carolina will see the sky darken as the sun disappears from view, albeit for only a few minutes at a time.

Temperatures in those areas could tumble by as much as 5.6 C, according to Paul Walker, a meteorologist with AccuWeather Inc. in State College, Pa. Other parts of the nation will only experience a partial eclipse.

“That is assuming a totally sunny sky. We will see a temperature drop where totality happens,” Walker said, referring to the path the eclipse will take across the U.S. where the sun will be completely blocked out.

The eclipse will disrupt the sun’s power to heat the ground, warm the atmosphere and supply electricity. It could also be ruined by a rainy day, patch of fog or even just a sudden thunderstorm in the wrong place. Given the limits of modern-day forecasting, predicting any one of those days in advance for an event that only lasts minutes is near impossible.

“It’s a difficult forecast challenge,” said Bob Henson, a meteorologist at Weather Underground in Boulder, Colo. “You’re not forecasting a day’s weather, but for two minutes.”

The chill in the air will peak about five to 20 minutes after the moon’s shadow passes by. Temperatures could take three hours to rebound across the Great Plains and East Coast, said Brad Harvey, meteorologist with MDA Weather Services in Gaithersburg, Md.

“The change in temperature may be larger and take longer to recover in the West,” Harvey said.

The eclipse will start to be seen in the morning, which is “the time of day when temperatures are rising most rapidly.”

As many as 12,000 megawatts of solar power will vanish along the path of the moon’s shadow along with the decrease in temperatures. Natural gas generators as well as hydroelectric plants and other sources will help fill in the gaps.