At a Glance

Past eclipses have changed the weather in the U.S. and Britain.Temperature, humidity and cloud cover all respond to the loss of sunlight.These changes are temporary, as the atmosphere usually recovers quickly.

Join us on The Weather Channel App at 4 p.m. EDT on July 2, 2019 as we bring you the 2019 Total Solar Eclipse live.

A total solar eclipse will occur Tuesday for much of South America, providing an opportunity to see how weather responds to the sun being obscured by the moon.

To start, here's what the weather is looking like for Tuesday's eclipse.

Current Forecast for the 2019 Eclipse

If past eclipses are any indication, Tuesday's eclipse won't disrupt any large weather systems, but small-scale changes are expected.

The 2017 Great American Solar Eclipse was one of the most documented total solar eclipses in human history, and there were several phenomena that can give us a few clues into what we'll see in Chile and Argentina.

1. Temperatures Dropped

Temperatures fell by as many as 12 degrees along the path of the eclipse. In theory, temperatures in arid climates and clear skies can fall as much as 15 degrees.

Temperature drops in North Carolina during the 2017 Great American Solar Eclipse.

In Argentina and Chile, there will be at least two differences that might make temperature drops less pronounced.

For one, the sun will be setting over the Atlantic while the eclipse is ongoing in parts of South America. This is in contrast to much of America where the sun was almost directly overhead in 2017. The end result is that the temperature drop in South America may not be as steep as they were in the United States.

Secondly, it is winter in the Southern Hemisphere. Clouds are expected to be somewhat more common and temperatures will already be cooler, which may further dampen the temperature decline.

2. Clouds Dissipated

During the temperature drop in 2017, clouds dissipated across the Carolinas. Most were shallow cumulus clouds that were driven by the heat of an August day in a fairly humid environment.

These clouds were initially driven by hours of sunshine and deep moisture across the region, and when the heat dropped out, the clouds couldn't sustain themselves.

These shallow clouds never recovered, but clouds that were self-sustaining deeper showers and thunderstorms were less affected and were able to bounce back.

Changes in cloud cover in the 2017 Great American Solar Eclipse.

While most of the clouds in South America are expected to be shallow, they are expected to be blanket stratus clouds along much of the path of the eclipse. Stratus clouds may not be as impacted by the loss of daytime heating as the puffy fair-weather cumulus clouds in America.

3. A Change in Winds Was Noted

Winds often slow down during an eclipse as the atmosphere temporarily settles.

Heating causes the atmosphere to mix and bubble, just like a pot of water on the stove. As it warms, the water level in the pot rises because warm objects, including water, expand. In the case of the atmosphere, it also expands when heated.

In contrast, when the atmosphere cools with a loss of sunshine, it shrinks and stabilizes.

Most winds are caused by local areas of heating, and when the heat goes away, so do the winds.

This effect was seen in , where winds fell from 20 mph to 10 mph or less, and , where the drop in wind speed was less severe outside the range of totality.

A by the University of Reading in the United Kingdom called this effect the "eclipse wind," which was defined as a change in wind direction and speed that occurs when the moon blocks out the sun.

More than 4,500 citizen scientists and a number of weather stations noted a subtle lessening of the wind in the path of a partial eclipse in the U.K. in 2015.

“As the sun disappears behind the moon, the ground suddenly cools, just like at sunset. This means warm air stops rising from the ground, causing a drop in wind speed and a shift in its direction, as the slowing of the air by the Earth’s surface changes," according to Professor Giles Harrison at the University of Reading.

Winds fell by just over 2 mph on average and changed direction by about 20 degrees, according to the study.

In 2017, scientists from the found that the minimum winds occurred as long as 25 minutes after totality. This lag is likely because the atmosphere takes such a long time to respond to losing heat.

4. Humidity Rose

Scientists at the University of Reading observed in relative humidity in the 40 minutes following totality in the U.S. The largest increases in humidity were seen where temperatures were warmest and the air was driest. The biggest climb in humidity was in the Plains, especially in Wyoming, according to the authors.

Even in the more muggy Southeast, a modest rise in humidity was seen as temperatures dropped closer to the dew point.