Picking out what to wear during the fall or spring can be tough. It might be sweater weather in the morning, only to feel more like summer heat by lunchtime. Or temperatures may start out in winter’s biting chill and suddenly warm up. It can be difficult to see 60 or 65 degrees Fahrenheit during a morning forecast and accurately anticipate what that will even feel like. There is actually a meteorological and a biological reason why the same temperature can feel different depending on the season.
The meteorological reason
When measuring the air temperatures that we see on daily forecasts, meteorologists generally use weather stations that are roughly six feet off of the ground. However, that distance does not take the ground temperature into account.
“In the summer, the ground is warm. As we start to cool and get into the cooler seasons, the ground changes temperature slower than the air around us,” New Hampshire-based meteorologist Cyrena Arnold tells Popular Science. “If you were to look at a graph of how the ground temperature changes with the seasons, and has less fluctuation, and it’s always kind of behind the seasons.”
[Related: Why autumn air smells so delicious and sweet.]
This is similar to how ocean temperatures in some parts of the world will feel colder over Fourth of July than they will over Labor Day in September. The liquid water and solid ground takes longer than air–a gas–to warm.
“So the air has warmth to it because it could be biased by the ground temperatures,” says Arnold. “Because the ground is still warm, we’re still feeling that warmth, that radiant heat.”
What the ground is made of also plays an effect. Concrete and asphalt are physically warmer than areas with grass or trees. That’s why walking around the city on a fall day generally can feel warmer than doing something like apple or pumpkin picking.
“The presence of trees, of grasses, of natural grounds, even if it’s just dirt, is really good and efficient at absorbing solar radiation and turning that into heat,” explains Arnold. “So the grass and the trees and all that turn that into energy, where on the asphalt it just gets hot. All that energy is just turned into heat.”
The biological reason
The old saying that “it’s not the heat, it’s the humidity” also applies in this situation. While humidity is generally a bigger factor during summer weather forecasts, it does not magically go away in the cooler months. Just like there is dry heat, there is also wet cold that can physically feel more uncomfortable.
“Our bodies have a natural air conditioner to 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 pulls 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 humid, you may sweat and it may never evaporate.”
Wet cold generally feels more uncomfortable than a dry cold because of the energy transfer that is going on between the three states of matter: solid, liquid, and gas. Gasses change temperature quickly, liquid a little more slowly, and solids the slowest.
In a dry cold, our bodies are still losing the energy from heat, but the air around us warms us more quickly because it is dry. This also relates to why we get goosebumps in the cold.
[Related: Satellite images of Las Vegas show just how extreme urban heat islands can get.]
“Your hairs stand on end because even the hairs on your arm are staying up a little bit trapped just enough air to keep your body warmer,” says Arnold. “Your hair is raised up to just trap this tiny layer of air near your skin to warm it up. If that air is humid, it’s going to take more energy to warm it up, so it’s going to pull more energy from you. If it’s pulling heat from you, it makes you feel cold.”
Where our capillaries are located also plays a role. The capillaries are tiny, delicate blood vessels that deliver oxygen, nutrients, and blood to cells throughout the body. They connect the arteries to veins and complete the circulatory system. According to Arnold, if our brains are like a thermostat that tells us if we are hot or cold, the capillaries work like the heater or 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’re closer to where our bodies sweat and where our skin cools.
“In the wintertime, those capillaries actually are a little bit deeper, where they have more insulation around them, where you’re losing less heat out to the atmosphere,” says Arnold.
There is also a degree of personalization to these feelings. Some people find 60 degrees to be colder in October, likely because their capillaries are still closer to the top of their skin and haven’t gone down deeper into our skin. Whereas, a 40 degree day in February may feel more like t-shirt weather, since our bodies are generally more acclimated to the cold temperatures.
“There’s just so many interesting things that happen meteorologically and biologically as to why the same temperature at two different seasons can feel different,” says Arnold.
You’ll just have to be prepared for the rollercoaster temperatures of fall and spring with layers and some patience.
The post Why 60 degrees in fall feels different than in the spring appeared first on Popular Science.