If you're looking for a desert climate, Joshua Tree is the place. Winter is mild (around 50°) during the day with icy nights, while summer is blistering hot and easily heads into the high 80°s and 90°s.
If you're flying, Palm Springs International Airport (PSP) is the convenient way to reach Joshua Tree. From the airport or from Los Angeles in general, it'll take you approximately two hours to drive out to the dessert. We highly recommend having your own four wheels to explore the area, especially during hotter months. The park also now offers a free shuttle service catered towards hikers that runs throughout the northern section of the park.