Right now in San Diego, the air is about 70°F, but the model estimates the asphalt under your dog's paws is closer to 70°F — the surface and air have nearly converged because the pavement is shedding the day's stored heat after dark. That reading puts San Diego in the clear for an ordinary walk. Air temperature alone would have told you none of this — the pavement, not the forecast, is what your dog actually stands on.
Across the 21 hours left today, the pavement in San Diego is projected to top out near 139°F around 1 PM, when the air will be about 88°F — a 51°F gap between the forecast your weather app shows and the surface your dog walks on. Today breaks into 2 separate safe stretches rather than one continuous window, so missing the first does not cost you the day.
In an average August, San Diego sees highs around 78°F and overnight lows near 66°F. Those are forgiving numbers, but don't let them lull you — a sunny, still afternoon can still heat dark asphalt far above the air, especially for low-riding or short-coated dogs. As a seasonal rule of thumb, the safest windows are before about 11:00 AM and after about 4:00 PM.
San Diego loses its all-day safe window in 5 months of the year — May through September — and August is one of them. The year peaks in September at an average high of 78°F against 63°F in March, a 15°F swing that decides how much of the day belongs to your dog.
San Diego sits about 7 miles from Chula Vista, close enough that the two usually run within a degree or two of each other — if your walk crosses between them, either page answers the question. Street-level conditions still differ more than city-level ones do: a shaded side street and an open parking lot half a block apart can be twenty degrees apart underfoot.
Whatever the number says, confirm it with your hand: press the back of it flat on the pavement for seven seconds. If you can't hold it there, neither can your dog. Conditions in San Diego are on the gentler side right now, but keep the same habits: water before and after, grass over asphalt, and a close eye on flat-faced breeds, seniors, and puppies, who overheat and burn sooner than a healthy adult dog.