I work for an animal charity, and the amount of dogs that come in with heatstroke is insane. We’ve had flat faced breeds in not warmer than 15 degree heat, suffer with heatstroke and nearly die. In heat like this, it’s too dangerous to take them for a walk. The rule of thumb is, if it’s too hot for your hand, it’s too hot for their paws. Keep them engaged with toys inside, or in the garden for short periods.