If you want to be sure at least some seeds germinate, use a wildflower mix.
Many suppliers formulate mixes especially for the Southwest. Wild Seed in Tempe, for example, offers a Sonoran Desert Native Wildflower Mix that includes arroyo lupine, California desert bluebells (Phacelia campanularia), bladderpod, desert lupine, desert marigold (Baileya multiradiata), desert senna, dyssodia, firewheel, owl's clover, penstemon, and verbena. No matter what the weather conditions, at least some of the seeds in your packet will likely germinate.
Some gardeners, however, prefer to buy packets of individual flower species and scatter them in drifts. California desert bluebells or other low growers near a pathway where they can be appreciated, for instance. Or penstemon near rocks for a natural look, since that's where they're often seen in the wild. If you want to try this technique (often called "painting" with seed), choose wildflowers that germinate readily, such as California and Mexican poppy (Eschscholzia), desert marigold, bluebells, and penstemon. Avoid more temperamental seeds, like owl's clover.