Hay vs esta

Question

One question was ____________  mucha niebla. Hay or esta.  I used esta wrong.  In fact mucha is never even translated.   So why is it Hay, not esta and why isn’t mucha translated

Answer

Hola Jim,
I checked the question in this quiz and yes, you are right, there was no translation for "mucha" , which in this case it'd be "very" when translating into English. Literally it would be saying "There is a lot of fog", but obviously that doesn't work in English, so it'd be "It is very foggy.".
With nouns like "niebla", "truenos", "relámpagos", or "tormenta" we use "Hay". With these idiomatic phrases talking about the weather there is a bit of memorising to do I am afraid. What we say in the lesson, as a tip, is that hay is followed by a noun: Hay + noun, as well as Hace + noun (Hace calor/Hace frío), and Está is followed by a gerund (lloviendo/nevando) or an adjective: Está nublado/soleado, but never by a noun, e.g. "Está sol"
Saludos
Inma

Answer

I have my own way of helping me remember some of these weather phrases. mucha and muy are clues that make it easy for me.

Ex. ________ mucha niebla. mucha is used before a noun. Therefore, niebla must be a noun, and you need to use Hay with a noun. So, Hay mucho niebla. There is a lot of fog. [or It is very foggy.]

Ex. ________ muy nublado. muy is used before an adverb or adjective. Therefore, nublado must be an adjective, and you need to use Está with an adjective. So, Está muy nublado. It is very cloudy.

This works whenever you see muy or mucha. It is Está muy ... or Hay mucha ... Hopefully, if you see enough sentences with muy and mucha, you will begin to remember the correct phrases even when those words aren't used.