Array.from(document.querySelectorAll(".temp__value,.fact__hour-temp")).forEach(e=>e.textContent=e.textContent.replace(/[-+]?[0-9.]+/g, t=>(t*9/5)+32))

... in the console, and it's almost entirely F. (except for the text summary at the top, which can include other numbers, so isn't safe to mess with this way). You could turn this into a bookmarklet and do this one-click. https://caiorss.github.io/bookmarklet-maker/

I know, totally impractical, no use on a phone, etc. I just wondered how easy it would be to fix.

(edited to add: lol, so mcluck had the same idea. the hour-temp and regex stuff in mine is because replacing just temp__value leaves the hour-by-hour temps in the top panel, which include the degree symbol as part of the text, so I want to leave that alone)

Array.from(document.querySelectorAll('.temp__value')).map(el => el.innerText = Math.floor(cToF(Number(el.innerText))))

Implementing cToF is left as an exercise for the reader