What this is about
You check the weather and see two numbers. The main reading says 12°C (54°F). Right below it, in smaller type, it says feels like 9°C (48°F). Then you glance out the window, notice the trees moving, and start doing extra mental math. If it feels like 9°C (48°F), plus the wind, should you bundle up for colder?
Stop there. The forecast already did that subtraction for you. Dress for 9°C (48°F) and leave it at that.
What the feels-like number counts
Wind cools a body by sweeping away the thin blanket of warm air trapped next to skin and fabric. An ordinary thermometer hangs in still air and shade, so it cannot measure that draft. The feels-like reading estimates how fast moving air strips that warmth away.
On a hot day, damp air works the other way. Sweat cools a body as it dries, and humid air slows the drying, so a muggy 30°C (86°F) feels hotter than a dry one. On a mild day with no wind, the two numbers are close or the same.
Weather apps call it feels like, RealFeel or apparent temperature, and US forecasts give it two names of their own: the wind chill in winter and the heat index in summer. They are all the same idea, worked out a little differently.
The difference can change the whole outfit
Three degrees may not sound like much on paper, but they often cross a clothing line.
12°C (54°F)Not good: Dressed for the thermometer
A light cardigan under a light jacket, thin socks and no hat. Right for a still day, and a layer short in this wind.
Feels like 9°C (48°F)Good: Dressed for feels like
A warm fleece under a warm jacket, booties over warm socks, and a light knit hat.
Count the wind once
When you see branches swaying, that gust is the reason the reading dropped below the air temperature. It explains why 12°C (54°F) feels like 9°C (48°F). It is not an invitation to subtract a second time. If you dress for 6°C (43°F), your baby will be sweaty and fussy ten minutes into the walk.
The wind still decides what goes on top. The number tells you how much warmth the outfit needs, and on a windy day the outside of the outfit has to keep that warmth in. That is the job of a smooth jacket or the footmuff's apron, not of a second sweater underneath.
When your walk feels different from the forecast
The forecast gives one number for the whole town, and its wind is measured on a mast, high above the ground. Between houses and under trees there is much less of it, while a bridge, a beach or a path along the water gets all of it.
The sun makes the bigger difference. The US wind chill assumes no sun at all, and some weather apps leave the sun out of their number while others add it in. On a cold, bright day, a baby sitting in the sun is warmer than the number says, and one step into the shade of a building takes that warmth away. So dress for the number, and open the jacket or the footmuff while your baby sits in the sun.
In summer the sun adds to the heat instead. The heat index on a US forecast is worked out for the shade, so on a hot day, a stroller parked in full sun sits in more heat than the number says.
The number changes through the day, too. The big one on the weather screen is for right now, and the feels-like moves more than the air as the sun and the wind come and go. Dress for the hour you leave, and if the hour you'll be back looks colder, take that layer along.
Indoors, the room thermometer takes over
Outdoor feels-like numbers belong on the street. The moment you step through a doorway, forget that number. A blustery 7°C (45°F) sidewalk and a calm 21°C (70°F) living room call for entirely different clothes.
On a morning of errands, the walk's outfit is too warm within minutes of a heated shop or bus, so open the jacket or the footmuff and take the hat off as you go in.
Room numbers don't work outside either. The 16–20°C (61–68°F) you read about for a baby's bedroom is about sleep, not about how warm a walk can be. At home, your guide is the room thermometer, and at night it is the one by the crib.
Questions parents ask
Is the feels-like number the same for my baby?
Close, but it's worked out for an adult. The wind chill was built from adult faces and tested only on adults, so take a little extra care with a child in the cold. A baby in the stroller also sits still while you walk and warm up, so a baby's outfit for any feels-like number has one light layer more than you would wear.
What heat index is too hot for a baby?
From a heat index of about 32°C (90°F), it is too hot for a long walk with a baby. Go out early or late, and keep to the shade.
What wind chill is too cold for a baby?
Most winter days are fine for a walk with a warmly dressed baby. Below 0°C (32°F) feels-like, keep to a short loop near home. At about −26°C (−15°F) feels-like, bare skin freezes within minutes, and that is the day to stay in.
It feels like below freezing, but the thermometer is above. Can my baby get frostbite?
No. Frostbite needs the air itself to be below freezing. The wind takes warmth from the skin faster, but it can't cool it below the air temperature. It can still dry and chap the cheeks, which is what wind cream is for.
Why do two weather apps show different feels-like numbers?
Each weather service works the number out its own way. Some add the sun, the clouds and the time of day, others count only the wind and the damp, so on a bright day they can be several degrees apart. Pick one app and stay with it. After a few walks, you'll know how its number fits your baby.
Why are my baby's hands cold if I dressed for feels like?
Cool hands and feet are normal outdoors, whatever the number. The back of the neck tells you more. If it is warm and dry, the outfit is right.
