Wind Chill & Dew Point

PLEASE READ FIRST
Figures published by your national weather service take precedence. Do not use
these numbers to decide what to do. The app does not fetch the temperature
where you are — you type the numbers in yourself. It does not produce WBGT
or any judgement about your health.

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🌬️ Wind Chill & Dew Point － type the numbers, see how the air feels

Enter -10 °C and a 20 km/h wind:

Feels like -17.9 °C
7.9 °C colder than the air
That wind in km/h: 20

Enter 28 °C and 70% humidity:

Discomfort index 78.4
A little hot
If humidity rises 10%: +1.3

■ Five tabs

▪ Discomfort index － from temperature and humidity. A Japanese everyday number
▪ Wind chill － from temperature and wind. The North American winter one
▪ Dew point － the temperature at which water starts to form on a surface
▪ Saturation － the most water 1 m³ of air can hold, with a table from -20 to 40 °C
▪ Water in this air － how much is in it now, and how much room is left

■ Below zero is the point

The temperature field takes a minus sign. If your keyboard has no sign key,
the ± button to the left of the field flips it. Winter is what this app is for.

■ Pick your wind unit

Japan forecasts wind in m/s, the wind chill formula wants km/h, and North
America uses mph. Enter whichever you have. The app also shows the km/h value
the formula actually used, so a mix-up shows up on screen instead of hiding
inside a correct-looking answer.

■ No stored tables

The app holds four formulas and no tables of data. Every table and every figure
is worked out the moment you open it, so no two numbers can disagree.

■ A Japanese index and a North American one, side by side

The discomfort index was devised in the United States in 1957, but it is Japan
that still quotes it daily. Wind chill was rewritten by Canada and the United
States in 2001 and appears in every North American winter bulletin. Two
countries describing hot and cold with two different formulas — both here.

■ One peculiar point in the formula

The discomfort index has a singular temperature: exactly 14.44 °C. At that
temperature the humidity makes no difference at all — 0% and 100% give the
same index. Above it humidity pushes the number up; below it, down.

■ Winter dryness, calculated

Take outdoor air at 0 °C and 60% humidity and warm it to 20 °C indoors. The
water in it has not changed, but the ceiling has risen, so the humidity falls
to 17%. The "water in this air" tab shows that swap directly.

■ The formulas used

Discomfort index (Thom, 1959)
Wind chill (JAG/TI, 2001 revision)
Dew point (Magnus formula)
Saturation vapour pressure and density (Tetens, over water)

The saturation figures match the standard published tables.

■ Good for

・Putting a number on a sticky summer night
・Knowing what temperature your windows start running with water
・Working out how much water a humidifier still has to add
・Understanding the wind chill figure in a bulletin from abroad
・Checking the moisture in a room where you keep instruments or books

■ Features

・No account needed
・One screen, no settings page
・Japanese and English, by device language
・History of the last five calculations
・Notes on every tab (19 in all)

Every figure is the plain result of the formulas listed above. Please do not
use them to make decisions about your health or your activities.

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NISAKE GAME