It can be difficult to choose what to wear during fall or spring. It may be sweater weather in the morning, but by lunchtime it feels more like summer heat. Or temperatures can start in the biting cold of winter and suddenly rise. 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 we see in daily forecasts, meteorologists generally use weather stations located about two meters above the ground. However, this distance does not take the ground temperature into account.
“In the summer the ground is warm. As we begin to cool and enter the cooler seasons, the temperature on the ground changes more slowly than the air around us,” says New Hampshire meteorologist. Cyrena Arnold tells Popular science. “If you were to look at a graph of how ground temperature changes with the seasons, fluctuates less, and it always lags the seasons a little bit.”
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This is similar to how ocean temperatures in some parts of the world will feel colder on the 4th of July than on Labor Day in September. Liquid water and solid soil take longer to heat up than air (a gas).
“The air therefore has a warm appearance, because it can be influenced by the ground temperatures,” says Arnold. “Because the ground is still warm, we still feel that heat, that radiant heat.”
What the soil is made of also plays a role. Concrete and asphalt are physically warmer than areas with grass or trees. That’s why a walk around town on a fall day can generally feel warmer than something like apple or pumpkin picking.
“The presence of trees, grasses and natural soil, even if it is just dirt, is very good and efficient at absorbing solar radiation and converting it into heat,” Arnold explains. “So the grass and the trees and everything that converts that into energy, while it just gets hot on the asphalt. All that energy is simply converted into heat.”
The biological reason
The old saying “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 doesn’t magically disappear in the colder months. Just as there is dry heat, there is also wet cold that can feel more physically uncomfortable.
“Our body has a natural air conditioning when we sweat. Our sweat glands release moisture onto the surface of our skin, cooling us as it evaporates,” says Arnold. “So it physically removes heat from your body and if the air is really dry, that evaporation happens very quickly and takes a lot less work. If it is damp, you may sweat and it may never evaporate.”
Wet cold generally feels more uncomfortable than dry cold because of the energy transfer that takes place between the three states of matter: solid, liquid and gas. Gases change temperature quickly, liquids a little more slowly and solids change the slowest.
In a dry cold, our body still loses energy from the heat, but the air around us warms us faster because it is dry. This also has to do with why we get goosebumps from the cold.
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“Your hair stands on end because even the hairs on your arm stand up a little, trapping just enough air to keep your body warmer,” says Arnold. “Your hair is raised to catch this tiny layer of air near your skin and warm it up. If that air is humid, it will take more energy to warm it, and so it will drain more energy from you. If it takes heat away from you, you get cold.”
Where our capillaries location also plays a role. The capillaries are small, 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 brain is like a thermostat that tells us whether we are hot or cold, the capillaries work like a heater or air conditioner.
In summer or in a warm climateThe capillaries are closer to the skin’s surface, so more heat can be released. They are closer to where our bodies sweat and where our skin cools.
“In the winter, those capillaries are actually a little bit deeper, where they have more insulation around them, so you lose less heat to the atmosphere,” says Arnold.
There is also a degree of personalization in these feelings. Some people find 60 degrees colder in October, probably because their capillaries are even closer to the top of their skin and have not penetrated deeper into our skin. While a 40 degree day in February may seem more like T-shirt weather, as our bodies are generally more acclimated to the cold temperatures.
“There are so many interesting things happening meteorologically and biologically that explain why the same temperature can feel different in two different seasons,” says Arnold.
You just have to be prepared for the rollercoaster temperatures of fall and spring with layers and some patience.