How do they determine the “feels like” temperatures for weather data?

Decoding “Feels Like” Temperature: What the Weather Report Really Means

Ever glance at the weather forecast, see a temperature, and then step outside only to think, “Wait a minute, this feels nothing like what they said!”? You’re not alone. That’s because the plain old temperature is just one part of the story. What you really want to know is the “feels like” temperature, also called the apparent temperature. Think of it as the weather’s attempt to tell you what it actually feels like to be outside, taking into account all the factors that affect your body.

So, how do these weather wizards conjure up this “feels like” number? It’s not just some random guess pulled from thin air. It’s a calculation, grounded in solid science. The big players in this calculation? Air temperature, naturally, but also humidity and wind speed. And, depending on whether it’s summer or winter, they tweak the formula to focus on what matters most for that time of year.

Humidity’s Hot Hand: The Heat Index

Let’s talk summer. When the air is thick and heavy, humidity becomes a major factor in how hot things feel. That’s where the heat index swoops in to save the day. This index blends air temperature and relative humidity to give you an idea of what the temperature feels like.

Why does humidity matter so much? Well, your body’s got its own built-in cooling system: sweat. When sweat evaporates, it carries heat away from your skin, like a personal air conditioner. But, when the air is already packed with moisture (that’s high humidity), sweat struggles to evaporate. It’s like trying to dry a towel in a steamy bathroom – it just takes forever. This slowdown in evaporation means your body can’t cool itself as efficiently, and you end up feeling way hotter.

The heat index isn’t a simple addition problem; it’s calculated using a rather complex formula:

HI = c1 + c2T + c3R + c4TR + c5T2 + c6R2 + c7T2R + c8TR2 + c9T2R2

Yeah, I know, it looks like something out of a math textbook. But here’s the gist:

• HI = Heat Index (in degrees Fahrenheit)
• T = Air Temperature (in degrees Fahrenheit)
• R = Relative Humidity (percentage)
• c1 through c9 are constants

This formula, cooked up by George Winterling back in 1978, works best when temperatures are baking (above 80°F or 27°C) and humidity is climbing (above 40%). The National Weather Service (NWS) keeps a close eye on this index to gauge heat stress levels and sound the alarm when things get dicey.

A word of caution: the heat index assumes you’re chilling in the shade. If you’re standing in direct sunlight, it’s going to feel even hotter than the index suggests. Think of it as the “feels like” temperature plus a sunburn bonus.

When the Wind Bites: Wind Chill

Now, let’s flip the script to winter. When the temperatures plummet, wind becomes the main culprit behind that bone-chilling feeling. Enter the wind chill, which tells you how much colder the wind makes it feel. Keep in mind, wind chill only matters when the temperature is 50°F (10°C) or below and the wind is blowing at more than 3 mph.

Here’s the deal with wind chill: Your skin creates a cozy little layer of warm air around itself, acting like a personal force field against the cold. But wind? Wind is a bully. It tears away that warm air layer, speeding up heat loss from your body. The stronger the wind, the faster it steals your heat, and the colder you feel.

The wind chill temperature is figured out using this equation:

Wind chill (ºF) = 35.74 + 0.6215T – 35.75(V^0.16) + 0.4275T(V^0.16)

Breaking it down:

• T = Air Temperature (in degrees Fahrenheit)
• V = Wind Speed (in mph)
• ^ = Raised to a power (exponential)

This formula is based on how heat moves away from your face and assumes a clear night. Also, they measure the wind speed at about 5 feet off the ground – roughly face-height for the average adult.

Of course, wind chill is a bit subjective. Things like body hair, lotions, and your own body’s ability to regulate temperature can all play a role.

The Big Picture

While heat index and wind chill are the headliners of “feels like” temperature, some weather services go even deeper, factoring in things like cloud cover, sunshine, and even how damp your skin is.

Look, the “feels like” temperature isn’t a crystal ball. Everyone experiences weather a little differently, depending on what they’re wearing, how active they are, and how used to the climate they are. But, it’s a handy tool for getting a better grip on how the weather might affect you. By paying attention to the “feels like” temperature, you can make smarter choices about what to wear and how to plan your day, so you can stay comfy and safe, no matter what Mother Nature throws your way.