Death Valley National Park, California
This parched desert park receives an average of less than 2 inches (5 centimeters) of rain per year. But what Death Valley lacks in moisture it makes up for in heat — in mid-summer, the temperatures there can kill you if you're not prepared. It's not uncommon for the mercury to hover at around 120 degrees F (49 degrees C) in July [source: NPS].
So perhaps it goes without saying that Death Valley is a very much wintertime destination. Daytime temperatures might require you wear a jacket (in the mid-60s F) but they're ideal for hiking. Nighttime temperatures are often brisk but only rarely plunge to freezing.
The more moderate temperatures mean you can hike and camp without crazy amounts of water and other provisions, although you should always be adequately prepared in this hard land, no matter the month — it is called "Death Valley" after all.
If you're lucky and there's a bit of rain here in January, you may witness a spectacular but brief wildflower season, which sometimes lasts into February, or at higher elevations, even into March. And ironically, even though the weather is more tolerable in winter, visitor numbers are actually lower this time of year than in spring, meaning that you may have some trails all to yourself [source: McManis].