Choosing what to wear during fall or spring can be difficult. It can be sweater weather in the morning, only to feel more like summer heat by lunchtime. Or temperatures can start out in the dead of winter and suddenly warm up. It can be difficult to see 60 or 65 degrees Fahrenheit during a morning forecast and accurately predict how it will feel. There is actually a meteorological and biological reason why the same temperature can feel different depending on the season.
The meteorological reason
When measuring the air temperatures we see in daily forecasts, meteorologists generally use weather stations that are about six feet off the ground. However, this distance does not take into account the temperature of the soil.
“In summer, the earth is warm. As we start to cool down and enter the colder seasons, the ground changes temperature more slowly than the air around us,” says New Hampshire meteorologist Cyrena Arnold. Popular science. “If you were to look at a graph of how the earth’s temperature changes with the seasons and there’s less fluctuation, and it’s always somewhat behind the seasons.”
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This is similar to how ocean temperatures in some parts of the world will feel colder during the Fourth of July than during Labor Day in September. Liquid water and solid earth take longer than air – gas – to heat up.
“So the air has warmth to it because it can be biased by ground temperatures,” Arnold says. “Because the earth is still warm, we’re still feeling that warmth, that radiant heat.”
What the soil is made of also plays an effect. Concrete and asphalt are physically warmer than areas with grass or trees. That’s why walking around town on a fall day can generally feel warmer than doing something like apple or pumpkin picking.
“The presence of trees, grasses, natural terrain, even if it’s just dirt, is really good and efficient at absorbing solar radiation and turning it into heat,” Arnold explains. “So the grass, the trees and everything that turns it into energy, where on the asphalt it just gets hot. All that energy is simply converted into heat.”
The biological reason
The old saying that “it’s not the heat, it’s the humidity” applies in this situation as well. While humidity is generally a bigger factor during summer weather forecasts, it doesn’t magically disappear in the cooler months. Just as there is dry heat, there is also wet cold which can physically feel more uncomfortable.
“Our bodies have a natural conditioner for them when we sweat. Our sweat glands release fluid onto the surface of our skin that cools us when it evaporates,” says Arnold. “So it physically draws heat from your body, and if the air is really dry, that evaporation happens very quickly and takes a lot less work. If it’s wet, you might sweat and it might never evaporate.”
Wet cold generally feels more uncomfortable than dry cold because of the transfer of energy occurring between the three states of matter: solid, liquid, and gas. Gases change temperature quickly, liquids a little more slowly, and solids more slowly.
In a dry cold, our bodies are still losing heat energy, but the air around us warms us faster because it is dry. This is also related to why we get lumps in the cold.
[Related: Satellite images of Las Vegas show just how extreme urban heat islands can get.]
“Your hair stands up because even the hair on your arm is getting a little trapped, just enough air to keep your body warmer,” says Arnold. “Your hair is raised to catch this little layer of air near your skin to warm it. If that air is moist, it will take more energy to heat it, so it will draw more energy from you. If it’s drawing heat from you, it makes you feel cold.”
Where our capillaries are located also plays a role. Capillaries are tiny, delicate blood vessels that deliver oxygen, nutrients, and blood to cells throughout the body. They connect the arteries to the veins and complete the circulatory system. According to Arnold, if our brain is like a thermostat that tells us whether we are hot or cold, the capillaries work like a heater or an air conditioner.
During the summer or in a warm climate, the capillaries are closer to the surface of the skin so that more heat can be released. They are closest to where our body sweats and where our skin cools.
“In the winter, those capillaries are actually a little deeper, where they have more insulation around them, where you’re losing less heat to the atmosphere,” says Arnold.
There is also a degree of personalization of these feelings. Some people think 60 degrees is colder in October, likely because their capillaries are still closer to the top of their skin and haven’t penetrated deeper into our skin. Whereas, a 40 degree day in February can feel more like t-shirt weather, as our bodies are generally more attuned to colder temperatures.
“There are so many interesting things going on meteorologically and biologically why the same temperature in two different seasons can feel different,” says Arnold.
You’ll just need to prepare for fall and spring temperatures with layers and a little patience.