Why r South facing mountains....

[kingofbedsit]

Why r south facing mountains warmer that north facing ones

[sddsddean]

You should add to the end of your question "in the Northern hemisphere". This is because the heat from the sun, which appears to be in the south if you are in the northern hemisphere, heats the south facing slopes whilst the north facing slopes remain in shadow. In summer the effect is lessened, but during winter is more pronounced as the sun is lower in the sky. In the southern hemisphere the reverse is true; north slopes are warmer than south.