Student or Learner
I can't understand what this sentence in bold suggests.
I think I've had a bit too much sun today - I've got a headache.
You're right - I might say "There was a lot of rain today" because rain is sort of measurable! I'll be honest, I can't really explain why I probably wouldn't say "There's a lot of sun today" - maybe it's just an anomaly with sun.
There's a lot of snow today. (It is snowing a lot today)
There's a lot of rain today. (It's raining a lot today)
There's a lot of cloud today. (It's very cloudy today)
There's a lot of fog today. (It's very foggy today)
BUT... for some reason, I would say "It's very sunny today" and not "There's a lot of sun". The only thing I can think is that the other weather types are sort of "tangible" (and also changeable), whereas the sun is just always there and it's either visible or it's not.
I don't think that was a very good explanation, for which I apologise!!!