Right now in San Mateo, the air is about 54°F, but the model estimates the asphalt under your dog's paws is closer to 54°F — the surface and air have nearly converged because heavy cloud cover is taking some of the edge off the direct sun. That reading puts San Mateo 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 17 hours left today, the pavement in San Mateo is projected to top out near 128°F around 2 PM, when the air will be about 86°F — a 42°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 Mateo sees highs around 74°F and overnight lows near 59°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 Mateo loses its all-day safe window in 4 months of the year — May through August — and August is one of them. The year peaks in August at an average high of 74°F against 56°F in December, a 18°F swing that decides how much of the day belongs to your dog.
San Mateo sits about 12 miles from Daly City, 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 Mateo 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.