"It is sunny and cold."
Translation:Tha i grianach agus fuar.
That's what is known as lenition. You need the 'h' in the phrase 'Àiridh Ghrianach' because àiridh is a feminine noun. Feminine nouns make adjectives lenite (ie add an 'h'). You don't need it in the above example because it is being used in isolation. Hope that helps! :)