It can cool down when the sun goes down. The first time I went I was actually shocked at how hot it was. I always heard how amazing Cali weather is and how much nicer the weather is at DL versus WDW but I found DL to be even hotter then WDW. I think its the fact that there are virtually no clouds in CA so the sun really beams down on you. Also the times I went there is a much greater difference between the cool down periods and the hot peaks. I was surprised that I was chilly in the morning, then uncomfortably hot and then chilly again int he evening. I was used to Florida where there isn't much of a difference between the afternoon and evening.
This is the case most of the time. What we are trying to say is that *currently* we are in a non typical weather pattern that is bringing much warmer temperatures and much higher humidity without the cooldown at night. Nights usually are in the mid 60s. It's been in the mid 70s lately for lows. That is not the norm, even for this time of year.