Typically, the heat is up in the 90s in the Harbor areas (Knott's,
Disneyland/DCA), but into the hundreds in the valley (Universal) and desert areas (Magic Mountain) <Both Universal and Magic Mountain are on hills, so the breezes do kick up a bit, but they are usually warm breezes>.
Keep in mind that Disneyland, unlike Disney World, is a dry heat. You will be hot, and you will be sweaty, but you won't be sticky.
I reccomend that you plan to do things around the water parts of the parks during the hottest parts of the day. I don't necessarily mean to do a water ride, such as Splash Mountain at Disneyland and GRR at DCA, but to be next to the large bodies of water. Stay in New Orleans/Frontierland at Disneyland in the heat - it is especially nice to get to the shade of Tom Sawyer's Island and have a break, or stay around the boardwalk area in DCA. The reason is that all that water creates cool breezes as it evaporates in the hot sun, thus lowering the temperature around those areas considerably. I hope this helps.
~Tina
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