Should be very nice that time of year, with mild daytime temps (mid 60s) though chillier nights if you're camping (low 40s). Just outside the winter "rainy" season, though it's hardly monsoon time out there in the desert. Definitely a good time to get out and enjoy the diverse desert scenery and wildlife. Given the mild days, though, it's also a popular time in the park for that very reason (ie, before brutal summer temps take root!).