The Sahara has low precipitation in part because the air passing over it has little moisture in it. Warmer oceans mean more evaporation and more precipitation

The Sahara has low precipitation in part because the air passing over it has little moisture in it. Warmer oceans mean more evaporation and more precipitation in some parts of the world. Hotter doesn't necessarily always mean drier. Additionally, desert environments generally have wild swings in temperature, so snow falling in a desert isn't unheard of. Global warming is not undermined by local events.