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Comment by Scoundreller | Hacker News Reader

And then you have other factors impacting a surface temperature including:

rainfall (you could probably spray the runway and it will cool down and be dry quickly…)

Length of day (we’re about 1 month past the summer solstice in the N. Hemisphere, and days are long in the northern latitudes)

Shade (unlikely on runways, they’re in the sun all day)

Wind (probably best anywhere on a runway unless it’s in a valley)

Cloud cover during the night: can’t radiate to the universe where it’s about -273C if clouds are in the way.

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Can you clarify how night cloud cover factors in? Do clouds really substantially reduce the radiative cooling capacity? Is that by functionally reflecting radiation back at the source (the earth)?

Broadly yes. It's why deserts have such extreme temperature fluctuations between day and night. No clouds are part of the reason, as well as very little humidity to serve the same heat-retaining/heat-reflecting role.

On my first time in the Nevada desert I was astonished to find that I needed a jacket at dawn to stay warm, after all kinds of daytime heat. Looking at Elko NV's weather this week, it's got highs of 99F/37C and overnight lows of 61F/16C

37C high earlier today and 16C low later tonight are coincidentally the exact numbers for my city in the UK. Which isn't of course anything like a desert, though the whole country is in the middle of a heatwave (and last night didn't drop below 20c).

Radiation is a function of the temperature delta between two points.

The sky around where clouds are might be around -20C, while outer space is at -273C or so, so you get much more radiative heat loss in the latter state (clear sky).

(This is also why you’ll see gardeners try to cover their plants when there’s a “frost warning” even though the temperatures won’t be going below freezing).

And from the opposite perspective, the sun is really far away but incredibly hot, so it transfers heat to us, and more as you get closer (and less as you get further away).

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