After sunset, the ground stops receiving direct sunlight but continues to release energy as infrared radiation. When it loses more energy than it receives from the atmosphere and its surroundings, the surface cools; the air in contact with it cools too. The National Weather Service calls this surface process radiational cooling.
How sunset cools the air
Sunlight warms Earth’s surface during the day. Once the Sun sets, incoming solar energy at the surface falls away, but the warmed ground continues emitting longwave, or infrared, radiation. If that energy loss exceeds the energy the surface receives from the atmosphere and nearby surroundings, the ground cools. The National Weather Service defines radiational cooling as “the cooling of the Earth’s surface.” National Weather Service glossary
The air temperature drops because heat moves from the air near the ground to the cooler surface. That distinction matters: the ground can cool faster than the air temperature reported by a standard weather observation, which represents air rather than the temperature of the soil, pavement, or other surface.
Why clear nights often cool faster than cloudy ones
Clouds emit infrared energy in multiple directions, including downward toward the surface. That energy can partly offset the ground’s heat loss, so, all else equal, a clear night often permits stronger surface cooling than a cloudy night. Cloud cover can also affect daytime heating, but its nighttime influence is to slow the surface’s loss of heat relative to clear skies. National Weather Service
#1 Best Overall
- DESIGN: Thermometer constructed of weather resistant and shatterproof materials for increased durability during use.
- PRECISION MEASUREMENT: Factory calibrated to accurately measure temperatures from -60 degrees Fahrenheit to 120 degrees Fahrenheit (-50 to 50 degrees Celsius)
- EASY TO USE: Bold black lettering with large numbers and a bright red pointer makes temperature readings easier.
- MULTIFUNCTIONAL: 8-inch indoor outdoor thermometer walls are placed in greenhouses, warehouses, baby rooms, offices, laboratories, balconies, gardens, terraces, etc
- TIPS: No batteries required. For the most accurate readings, place out of direct sunlight.
How wind and humidity change the cooling
Wind mixes air near the ground
On a clear night with light winds, the air closest to the surface can cool more rapidly than air above it. This creates a shallow temperature inversion: instead of getting colder with height near the ground, the air is colder below and warmer above. Stronger mixing changes that near-ground temperature contrast. Wind can also carry in a different, warmer or colder air mass, so wind speed alone does not determine whether a night will cool.
Humidity and clouds are different influences
Water vapor in the air affects how quickly the surface loses energy. The Met Office notes that dry air can allow more rapid cooling overnight and a larger difference between daytime and nighttime temperatures. Humidity and cloud cover can both influence cooling, but they are not interchangeable: clouds affect the exchange of infrared energy, while water vapor is present in the air itself. Met Office
Rank #2
- DESIGN: Thermometer constructed of weather resistant and shatterproof materials for increased durability during use.
- PRECISION MEASUREMENT: Factory calibrated to accurately measure temperatures from -60 degrees Fahrenheit to 120 degrees Fahrenheit (-50 to 50 degrees Celsius)
- EASY TO USE: Bold black lettering with large numbers and a bright red pointer makes temperature readings easier.
- MULTIFUNCTIONAL: 5.25-inch indoor outdoor thermometer can be mounted in greenhouses, warehouses, baby rooms, offices, laboratories, balconies, gardens, terraces, etc
- TIPS: No batteries required. For the most accurate readings, place out of direct sunlight.
Why the coldest point is usually later than sunset
Sunset marks the end of direct solar input at the surface, not the instant the ground and air reach their lowest temperatures. The surface and air absorb and release heat at different rates, and heat continues to move through the ground and atmosphere after dark. Thermal inertia—the tendency of materials and the air to warm and cool at different rates—helps explain why the daily minimum is not necessarily reached at sunset. Wind and changing air masses can also alter the temperature profile through the night. Met Office
What to expect on different nights
| Condition | Typical effect | Important qualification |
|---|---|---|
| Clear rather than cloudy | Often allows faster surface radiational cooling. | Clouds and changing weather can complicate the comparison; it is a tendency, not a guarantee. National Weather Service |
| Light wind rather than stronger mixing | Can favor a shallow inversion, with the air nearest the ground cooling faster than air above. | Wind can transport a different air mass as well as mix the air. National Weather Service |
| Dry rather than humid air | Dry air can allow quicker overnight cooling and a larger daily temperature range. | Humidity is only one influence; cloud cover, wind, and thermal inertia matter too. Met Office |
Why there is no universal overnight temperature drop
The amount and pace of cooling depend on local conditions, including cloud cover, humidity, wind, the ground, and changes in the surrounding air. A clear, calm night may favor strong cooling near the surface, but those conditions do not guarantee a particular temperature drop or a specific time for the nightly low. These general principles explain the process; a local forecast is needed to estimate temperatures for a particular place and night.
The Tool Desk
Outbyte PC Repair FREERepair Windows errors before they cause bigger problemsFix Now →Outbyte Driver Updater FREEScan for outdated or missing drivers - takes under a minuteDriver Scan →Rank #3
- HIGH-PRECISION TEMPERATURE HUMIDITY GAUGE – Our air indoor thermometer and hygrometer has a Swiss-made high-precision sensirion sensor that makes it extremely accurate! The indoor temperature range is +14.2ºF~+122ºF, the outdoor temperature range is -58ºF~+158ºF, the indoor/outdoor humidity range is 1~99%, the temperature accuracy is +/-0.5ºF and the humidity accuracy is +/-2%.
- PATENTED TECHNOLOGY – Unni has advanced patented wireless technology that provides more powerful and steady data transmission. Personal wireless temperature humidity monitor updates and transmits temperature and humidity data up to 330 ft radius every 30 seconds, that will help you monitor all the locations you care about the most.
- SPECIAL FEATURES – Stop worrying about the climate! With our wireless hygrometer thermometer gauge, you will be able to know in real time the weather forecast, as well as the indoor and outdoor temperature and humidity. You can also see on the display of heat index , the dew point index and the mold index of all the sensor locations.
- LARGE CLEAR BACKLIT DISPLAY – The display is compact and easy to read with black, bold information. With a tabletop or wall-mountable design, you can place it in a location that is accessible and easy for you to view. Tap the back light button and it will light up for 10 seconds for you to read in dark.
- WHAT YOU GET – You get the indoor thermometer with a display screen, an outdoor sensor, one-year warranty(not including batteries). Support up to 3 sensors, make sure they are in different channels.
If you are curious about the pattern at home, an outdoor thermometer can help you compare evening and morning readings. It is optional; the explanation does not depend on taking measurements.
Quick Recap
Rank #4
- COMPLETE WEATHER STATION: (1) Osprey Sensor Array with Rain Cup, and (1) Brilliant, Easy-to-Read LCD Color Display
- AUTHENTIC HYPER-LOCAL DATA: Monitor your actual home and backyard weather conditions with our wireless and Wi-Fi-enabled sensor array measuring wind speed/direction, temperature, humidity, rainfall, UV intensity, and solar radiation
- SMART HOME READY: Set up alerts, access your data remotely, and program your home based on weather conditions using IFTT, Google Home, Alexa, and more
- ENHANCED WIFI: Enables your station to transmit its data wirelessly to the world's largest personal weather station network (optional setting)
- JOIN THE COMMUNITY: Connect to Ambient Weather Network to customize your dashboard tiles, share hyperlocal weather conditions via social feeds and create your own forecasts (coming soon)
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
