(CNN) — Wednesday’s total solar eclipse will alter weather conditions along its path from the Arctic to western Europe.
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Changes to temperature, wind speed and humidity occur as the moon crosses in front of the sun during a solar eclipse and casts a shadow on Earth’s surface. This reduces the amount of solar radiation — sunlight and energy – that makes it to the surface.
The more solar radiation blocked, no matter how brief, the more dramatic the weather changes. The effect is comparable to how shaded areas end up much cooler on a hot day than any place in direct sunlight.
Wednesday’s eclipse will completely block out the sun along a narrow path in northern Russia, parts of Greenland, Iceland, Portugal and Spain, providing the opportunity for more noticeable changes in spots.
Not all eclipse weather changes are created equal, though. The exact drop in temperature can vary widely based on other factors like cloud cover and the time of year.
The biggest temperature drops usually happen during sunny summer afternoons when the sun angle is high in the sky. A higher sun angle produces more intense sunshine and elevated temperatures, so thermometers are more prone to cratering with a loss of solar radiation.
This drop can be as much as 8 to 14 degrees Fahrenheit in areas with low humidity, according to the National Oceanic and Atmospheric Administration.
Temperatures start to fall slowly as the eclipse begins, but they don’t completely bottom out until after totality is over, as temperature changes lag behind solar radiation fluctuations.
In the August 2017 US eclipse, temperatures didn’t hit their lowest point until about 5 to 10 minutes after totality in the lower Ohio Valley.
Wednesday’s eclipse will happen in the afternoon in Iceland and Greenland, but how much the temperature falls will depend on cloud cover, which could be fairly abundant in those areas. Clouds reduce temperature drops because they already block some solar radiation.
Totality in Portugal and Spain will happen shortly before sunset. That means temperatures might drop somewhat faster before the sun falls below the horizon than they normally would, but are unlikely to drop as dramatically as they would earlier in the afternoon.
An eclipse affects more than just temperature
Less solar radiation and reduced temperatures can also affect wind, cloud cover and humidity.
The quick cooldown during an eclipse briefly reduces the amount of heat stored in the atmosphere. Heat forces air to rise and makes the atmosphere unstable. The atmosphere then creates clouds, storms and wind to let out heat energy in an attempt to bring itself back into balance.
As the eclipse cools the air, the atmosphere calms down and wind speeds drop because it isn’t working as hard to balance itself out. Scientists took a number of weather measurements in Wyoming and New York during 2017’s total solar eclipse and found wind speeds dropped by an average of 6 mph as a result of the eclipse.
A significant temperature drop can also alter cloud cover.
Clouds over parts of northern Texas decreased during the 2024 total solar eclipse because they lost their fuel — heat that forces air to rise and form clouds.
How humid it feels is also tied closely to temperature. Humidity rises when the air temperature and the dew point, which measures how much moisture is in the air, approach the same temperature. So when air temperatures briefly dip during an eclipse, they trend closer to the dew point and make the air feel a bit more humid.
The next total solar eclipse will happen about a year from now on August 2, 2027. Parts of southern Spain, northern Africa, Saudi Arabia and Yemen are in the path of totality.
The next time totality will be visible in the US will be in Alaska on March 30, 2033.
The-CNN-Wire
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