It depends if you are camping or not. The desert is all about extremes, so plan on very cold weather at night and livable/cool during the day - however, it also means that snow storms can roll in and make roads impassible overnight and the daytime melt can cause flooding. If you are staying in town, none of this would be a problem because the plans can be altered to account for the weather, but backcountry travel can be hazardous.