Describing Current/Past Temperatures

[Bobbert]

When describing the temperature in the present or the past, I'm not sure which verb or conjugation to use.

I want to say:

Last week in Chicago, it was 18 degrees below zero with a windchill of 32 below zero.

Some translators on the internet use está a/estaba a, hace/hacía/había, and es/era when speaking about temperatures, so needless to say, I am totally confused.

What is the best way to translate the above sentence?

My attempt: La semana pasada en Chicago estaba a 18 grados bajo cero con una sensación térmica de 32 bajo cero.


Any rules/guidelines you can give me regarding how to describe the current as well as past temperatures is appreciated.
I don't need help in describing weather conditions or that sort of thing; just temperatures.