If a weather expression refers to a phenomenon that can be felt —good weather, cold, hot, windy— use the verb hacer - hace calor, hace frío, etc.
*If it is a condition results from a specific phenomenon, use estar – está nublado (it is cloudy- because there are clouds), está soleado (it is sunny – because there is sun)
**If a weather condition can be seen, use haber – hay neblina (it is foggy), hay nubes (it is cloudy).
Hester Chamberlain
Learning Assistance Center
Eastfield College