I think this proves that I have an unhealthy addiction to milk.
(I didn't check the temperature until after I came home from buying the milk. I just unreasonably assumed that at 7:15 p.m., it couldn't possibly still be over 100 degrees. And I really should have known better than to assume that, after having already lived through 30 other summers in the hellish heat of Sacramento.)
Actually, I had been expecting that when I woke up this morning, my legs would be too sore from walking to work yesterday for me to be able to walk to buy milk, no matter what the weather was. But they weren't sore. They must have gotten stronger since last weekend, when they were plenty sore from climbing around on the Sutro baths.