What Is the Dew Point, and How Does It Relate to Humidity?

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iStock

Humidity has been a part of weather forecasts for as long as we’ve gotten our news over the air. At the beginning of most weather forecasts, our friendly neighborhood weatherperson tells us the sky conditions at the moment, the current temperature, and the relative humidity. Over the past couple of decades, though, the relative humidity has started to fall by the wayside in favor of the dew point. The dew point is a much more useful measure of how much moisture is in the air, but how does it relate to relative humidity?

The amount of water vapor in the air can dictate what kind of weather we see and how comfortable we are once we step outside. Relative humidity is technically defined as the air’s vapor pressure divided by its equilibrium vapor pressure. Equilibrium vapor pressure means that “there is no net evaporation or condensation,” according to Alistair Fraser, professor emeritus of meteorology at Penn State. At the equilibrium, otherwise known as the saturation point, water molecules are entering and leaving the condensed state at the same rate. When the relative humidity is cited as 50 percent, that means that the air is halfway to its saturation point, and that net evaporation is occurring. Warm air requires more water vapor than cool air to reach its saturation point, which is why an 85°F afternoon can get much muggier than a day that only makes it to 50°F—the latter can still be humid, sure, but it’s not like walking into a sauna.

The dew point is the temperature to which the air needs to cool down to in order to become completely saturated, or reach 100 percent relative humidity. Once the air temperature cools below its dew point, water vapor in the atmosphere will condense. This causes the relative humidity to go up and down like a roller coaster during the day. The relative humidity will go up at night when the air temperature approaches the dew point, and the relative humidity will go down as the air temperature warms farther and farther away from the dew point during the day.

The dew point is a little more abstract than the relative humidity, but it’s an effective way of telling you how much moisture is present in the air because it means the same thing no matter how warm or cold it is outside. A 40°F dew point is comfortable whether the air temperature is 60°F or 100°F. This consistency allows us to index the dew point to comfort levels, giving us a quick understanding of how muggy or pleasant it is outside.

It’s downright dry outside when the dew point is at or below the freezing point. Dew point readings between the freezing mark and about 55°F are pretty comfortable. A dew point between 55°F and 60°F is noticeably humid. It’s muggy when the dew point is above 60°F, and it’s uncomfortable outside when it ticks above 65°F. Any dew point readings above 70°F are oppressive and even dangerous, the kind of stickiness you experience in the tropics or during a brutal summer heat wave. It’s rare for the dew point to reach 80°F, but it can happen in extremely moist areas like corn fields or certain tropical areas.

The dew point and relative humidity are closely related, but the former is much more useful than the latter. Relative humidity helps meteorologists predict conditions favorable for wildfires and fog. Other than that, it’s mostly a relic of the old days that show up in weather reports out of habit. If you want to know the true measure of how comfortable or muggy it is outside, take a look at the dew point.

10 of the Best Indoor and Outdoor Heaters on Amazon

Mr. Heater/Amazon
Mr. Heater/Amazon

With the colder months just around the corner, you might want to start thinking about investing in an indoor or outdoor heater. Indoor heaters not only provide a boost of heat for drafty spaces, but they can also be a money-saver, allowing you to actively control the heat based on the rooms you’re using. Outdoor heaters, meanwhile, can help you take advantage of cold-weather activities like camping or tailgating without having to call it quits because your extremities have gone numb. Check out this list of some of Amazon’s highest-rated indoor and outdoor heaters so you can spend less time shivering this winter and more time enjoying what the season has to offer.

Indoor Heaters

1. Lasko Ceramic Portable Heater; $20

Lasko/Amazon

This 1500-watt heater from Lasko may only be nine inches tall, but it can heat up to 300 square feet of space. With 11 temperature settings and three quiet settings—for high heat, low heat, and fan only—it’s a dynamic powerhouse that’ll keep you toasty all season long.

Buy it: Amazon

2. Alrocket Oscillating Space Heater; $25

Alrocket/Amazon

Alrocket’s oscillating space heater is an excellent addition to any desk or nightstand. Using energy-saving ceramic technology, this heater is made of fire-resistant material, and its special “tip-over” safety feature forces it to turn off if it falls over (making it a reliable choice for homes with kids or pets). It’s extremely quiet, too—at only 45 dB, it’s just a touch louder than a whisper. According to one reviewer, this an ideal option for a “very quiet but powerful” heater.

Buy it: Amazon

3. De’Longhi Oil-Filled Radiator Space Heather; $79

De’Longhi/Amazon

If you prefer a space heater with a more old-fashioned vibe, this radiator heater from De’Longhi gives you 2020 technology with a vintage feel. De’Longhi’s heater automatically turns itself on when the temperatures drops below 44°F, and it will also automatically turn itself off if it starts to overheat. Another smart safety feature? The oil system is permanently sealed, so you won’t have to worry about accidental spills.

Buy it: Amazon

4. Aikoper Ceramic Tower Heater; $70

Aikoper/Amazon

Whether your room needs a little extra warmth or its own heat source, Aikoper’s incredibly precise space heater has got you covered. With a range of 40-95°F, it adjusts by one-degree intervals, giving you the specific level of heat you want. It also has an option for running on an eight-hour timer, ensuring that it will only run when you need it.

Buy it: Amazon

5. Isiler Space Heater; $37

Isiler/Amazon

For a space heater that adds a fun pop of color to any room, check out this yellow unit from Isiler. Made from fire-resistant ceramic, Isiler’s heater can start warming up a space within seconds. It’s positioned on a triangular stand that creates an optimal angle for hot air to start circulating, rendering it so effective that, as one reviewer put it, “This heater needs to say ‘mighty’ in its description.”

Buy it: Amazon

Outdoor Heaters

6. Mr. Heater Portable Buddy; $104

Mr. Heater/Amazon

Make outdoor activities like camping and grilling last longer with Mr. Heater’s indoor/outdoor portable heater. This heater can connect to a propane tank or to a disposable cylinder, allowing you to keep it in one place or take it on the go. With such a versatile range of uses, this heater will—true to its name—become your best buddy when the temperature starts to drop.

Buy it: Amazon

7. Hiland Pyramid Patio Propane Heater; Various

Hiland/Amazon

The cold’s got nothing on this powerful outdoor heater. Hiland’s patio heater has a whopping 40,000 BTU output, which runs for eight to 10 hours on high heat. Simply open the heater’s bottom door to insert a propane tank, power it on, and sit back to let it warm up your backyard. The bright, contained flame from the propane doubles as an outdoor light.

Buy it: Amazon

8. Solo Stove Bonfire Pit; $345

Solo Stove/Amazon

This one is a slight cheat since it’s a bonfire pit and not a traditional outdoor heater, but the Solo Stove has a 4.7-star rating on Amazon for a reason. Everything about this portable fire pit is meticulously crafted to maximize airflow while it's lit, from its double-wall construction to its bottom air vents. These features all work together to help the logs burn more completely while emitting far less smoke than other pits. It’s the best choice for anyone who wants both warmth and ambiance on their patio.

Buy it: Amazon

9. Dr. Infrared Garage Shop Heater; $119

Dr. Infrared/Amazon

You’ll be able to use your garage or basement workshop all season long with this durable heater from Dr. Infrared. It’s unique in that it includes a built-in fan to keep warm air flowing—something that’s especially handy if you need to work without wearing gloves. The fan is overlaid with heat and finger-protectant grills, keeping you safe while it’s powered on.

Buy it: Amazon

10. Mr. Heater 540 Degree Tank Top; $86

Mr. Heater/Amazon

Mr. Heater’s clever propane tank top automatically connects to its fuel source, saving you from having to bring any extra attachments with you on the road. With three heat settings that can get up to 45,000 BTU, the top can rotate 360 degrees to give you the perfect angle of heat you need to stay cozy. According to a reviewer, for a no-fuss outdoor heater, “This baby is super easy to light, comes fully assembled … and man, does it put out the heat.”

Buy it: Amazon

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5 Ways to Help Victims of the West Coast’s Wildfires

A wildfire near Shaver Lake, California, earlier this month.
A wildfire near Shaver Lake, California, earlier this month.
David McNew/Getty Images

Wildfires continue to ravage millions of acres across California, Oregon, and Washington, and strong winds forecasted in some of those regions could aggravate the blazes. To prevent future fires, we need to focus on combating climate change through policy reform and sustainable living. But for people directly affected by the fires, their current needs are much more urgent: food, shelter, and funds. Here are five organizations that can help you help victims.

1. Red Cross

The Red Cross has about 600 workers coordinating meal distribution, installing victims in shelters and hotels, and providing other support across Northern California. You can donate to the cause by choosing “Western Wildfires” under “I Want to Support” on the donation page here.

2. GoFundMe

GoFundMe’s affiliated nonprofit, GoFundMe.org, has created a Wildfire Relief Fund for this particular outbreak of fires on the West Coast. You can make a donation to the overall fund here, or you can explore the separate hubs in the description to find individual GoFundMe pages to give to.

3. Los Angeles Fire Department Foundation

Unfortunately, the city of Los Angeles doesn’t allocate enough public funds to the fire department to equip firefighters with all the important gear they need. The Los Angeles Fire Department Foundation tries to fill those demands by providing things like hydration backpacks, thermal-imaging cameras, brush-clearing tools, and more. You can donate to the general fund here, or choose a specific fire station from the dropdown menu.

4. VEMAnet

VEMAnet (Volunteers for the Emergency Management of Animals Network), is an offshoot of the Good Shepherd Foundation, which links animal owners who need emergency help with volunteers who can transport and/or house their animals—anything from cats to cattle—temporarily. You can post details about what animals you can accommodate here; and if you or someone you know needs help evacuating any pets, you can request help or browse available listings here.

5. California Fire Foundation

The California Fire Foundation’s Supplying Aid to Victims of Emergency (SAVE) program distributes $250 gift cards to wildfire victims, so they can decide for themselves what their most pressing needs are. You can donate here.