It's way too hot—is the weather forecast fake? Unboxing a mechanical thermometer

Preface

PS: what? You can unbox a thermo-hygrometer?

It's been ridiculously hot lately

Every summer I start doubting how accurate the weather forecast is

I clearly feel unbearably hot, but the weather forecast still blandly says it's under 34 degrees

The science

I only found out after reading a science explainer on Zhihu that it isn't that the weather forecast is inaccurate—it's that the air temperature and the actual apparent temperature aren't the same

The air temperature data in our weather forecasts uses the internationally standard Stevenson screen method (a well-ventilated white box 1.5 meters above the ground). This internationally standard method measures atmospheric physical parameters that are not disturbed by local conditions, which is useful for climate records and statistical standardization. Its purpose is not to correctly indicate apparent temperature.

This Stevenson screen method is indeed very scientific, and the temperature it measures is very standard, but damn it, outdoor workers aren't working inside a well-ventilated white box 1.5 meters above the ground! 😂

This also explains quite well why the temperature doesn't look that high, but it actually feels so hot...

Heat Index

This heat index can represent the apparent temperature.

The original formula is a regression equation based on Fahrenheit (°F) and relative humidity (%):

HI = -42.379 + 2.04901523*T + 10.14333127*RH 
     - 0.22475541*T*RH - 0.00683783*T*T - 0.05481717*RH*RH 
     + 0.00122874*T*T*RH + 0.00085282*T*RH*RH - 0.00000199*T*T*RH*RH

Where:

• T is the temperature in Fahrenheit
• RH is humidity (percentage)
• HI is the result, still in degrees Fahrenheit

Conversion between Celsius and Fahrenheit:

T_F = T_C * 9/5 + 32

Based on this formula, I implemented a Heat Index calculator in csharp, and using today's daytime temperature and humidity (measured with a thermometer), 36 degrees, 70% humidity, the calculated HI value was as high as 54.15°C!

{
  "TempCelsius": 36,
  "HumidityPercent": 70,
  "HeatIndexC": 54.150858231555645
}

And HI above 41°C is already the extremely dangerous level that can lead to heatstroke, so you can imagine how hot it is 🥵

Thermo-hygrometer

I already had a Xiaomi thermometer and a Deli thermometer

This time while scrolling on a certain Xixi, I saw a purely mechanical thermo-hygrometer that doesn't need batteries, so I picked up two of them.

Packaging

OK, back to the topic

Let's start with some photos

The white balance on the photo below seems to have gone haywire

Unboxing

Looks kinda tacky 😂

There's a stand on the back

Random aside

I previously suspected one of the AC remotes wasn't very responsive

So I bought a new remote

I only took one photo

It's practically identical to the original

References

• Why does it feel so much hotter than the weather forecast?
• Heat Index Calculator