Your body needs to lower its core temperature by about 1–2°C to initiate and maintain deep sleep. This is why cool rooms dramatically improve sleep quality. They help accelerate that drop.

The scientific consensus points to 15–19°C (59–66°F) as the optimal bedroom range, with 16°C being the most commonly cited ideal. Above 20°C, the body struggles to shed heat efficiently, reducing slow-wave and REM sleep.

This forecast estimates your indoor temperature by combining the outdoor night temperature with a heat retention factor: the hotter your day was, the more warmth your home will hold into the night.

You spend 7 to 9 hours each night continuously breathing whatever is in your room, so the air you sleep in matters. This forecast uses the European Air Quality Index (EU AQI), a single 0 to 100+ measure where lower is cleaner, divided into bands: good, fair, moderate, poor, and very poor.

The EU AQI is a composite. It combines several pollutants and reports the worst offender, so one bad pollutant is never hidden by the others. The Air quality row in the conditions list breaks out each pollutant individually:

PM2.5 and PM10 are fine and coarse particulate matter. The smallest particles reach deep into lung tissue, and elevated levels are linked to reduced sleep efficiency, more night-time awakenings, and shorter sleep. Ozone (O₃) at ground level is a reactive, irritant gas formed when sunlight hits traffic and industrial emissions; it can inflame airways and bother people with asthma or allergies, and tends to be highest in summer and in cities. Nitrogen dioxide and sulphur dioxide come mainly from traffic and combustion and irritate the airways. Carbon monoxide is tracked as a general marker of combustion pollution.

A bedroom with no air movement can feel stale and stuffy. As you sleep you exhale carbon dioxide and give off heat and moisture, and without fresh air that builds up through the night.

A gentle breeze outside helps replace stale indoor air with fresh air when a window is open, and the light movement can keep a room feeling cooler and more comfortable. This is the sweet spot the forecast rewards.

Strong wind works against you. It can rattle windows, whistle through gaps, and create sudden gusty noise that disturbs light sleep, so the forecast treats high wind speeds as a negative.

A gentle, steady rain can genuinely help you sleep, in a few different ways.

It softens sound. Light to medium rain produces a steady, broadband sound often described as pink noise: consistent across frequencies, so it gently masks sudden noises like traffic, doors, or voices that would otherwise jolt you awake. Many people find this calming, and it can make falling asleep easier and sleep less fragmented. It is the same reason steady rainfall is so common in sleep and relaxation recordings.

It cleans the air. As droplets fall they collect pollen, dust, and other fine particulate matter, which is why the air often feels fresher once a shower has passed. For anyone sensitive to allergens, that can mean easier breathing through the night.

It may ease pressure. Barometric pressure usually falls in the day or two before a storm, and that drop is linked to headaches, sinus pressure, and achy joints in sensitive people. Once the front moves through and pressure settles, that heavy, unpleasant feeling tends to ease, which is part of why the air can feel like it has "released" after rain. The effect varies a lot from person to person.

Heavy rain is different. Loud downpours, thunder, and gusty wind can be jarring rather than soothing. That is why this forecast rewards gentle, steady rain but treats heavy rain as a potential disturbance.

Your body relies on darkness to release melatonin, the hormone that signals it is time to sleep. As light fades in the evening, melatonin rises and you start to feel drowsy.

In summer, long days push sunset late into the evening, sometimes past 9pm. That lingering evening light keeps melatonin suppressed for longer, delaying the natural signal to wind down. The effect is one reason many people find it harder to fall asleep on bright summer nights, even when everything else is comfortable.

This forecast looks at how late the sun sets. The later it gets dark, the more evening light there is to work against an early, easy bedtime.

Humidity affects how well your body can cool itself through perspiration. Too low (under 40%) and your airways dry out, leading to snoring, congestion, and restless sleep. Too high (above 60%) and it becomes difficult for sweat to evaporate, making you feel hot and clammy.

The 40–55% range keeps airways comfortable and allows effective thermoregulation throughout the night.

The idea that the full moon disrupts sleep has been dismissed as folklore for centuries, but the evidence is more nuanced. A well-cited 2013 study in Current Biology found that around the full moon, participants took 5 minutes longer to fall asleep, slept 20 minutes less overall, and showed reduced deep-sleep brain activity, even in a windowless lab with no moonlight exposure.

The leading hypothesis involves circadian rhythm entrainment: human biology may have evolved a subtle internal lunar rhythm. A secondary mechanism is simply light exposure. A bright full moon rising early can suppress melatonin, especially through uncovered windows.