# Why is cloud base estimation taught in Fahrenheit?

I've seen the formula for estimating cloud base consistently presented using Fahrenheit temperature and dewpoint (for example, see PHAK 12-14; Jeppesen also teaches it this way):

$$\mathrm{cloud\:base} \approx \frac{(\mathrm{temperature\:°F})-(\mathrm{dewpoint\:°F})}{4.4\mathrm{°F}} \times 1000'$$

However, a METAR always gives temperature and dewpoint in Celsius, and pretty much everything else in aviation uses Celsius — even lapse rate, which is the basis for this formula, is taught as "2°C per 1000 feet". It seems to me that using °F in this formula invites error, since temperature and dewpoint must first be converted to Fahrenheit before using this formula. If the constant on the bottom of the fraction were $$2.4 \mathrm{°C}$$ then the formula could be used directly with numbers from the METAR.

Is there a specific reason why this formula is given in °F?

• Where are you doing your studying? I ask because in the US, I can't instantly remember any temperatures in anything other than Fahrenheit... Dec 13, 2020 at 18:34
• I’m studying in the U.S. (Washington DC area). However, I think all AWOS systems I’ve interacted with give temps/dewpoints in Celsius. Mar 2, 2021 at 22:08