A hybrid powertrain system includes an engine and an electric machine respectively connected to first and second drive axles, with the electric machine decoupled from the engine. The system includes a battery pack and a controller. The controller has slip integrators with a corresponding integrator value for a given one of the drive axles. The integrator values are indicative of an accumulated amount of drive wheel slip over a calibrated duration or window. The integrator values change responsive to axle torque and traction control status signal. The integrator values are added together to derive an integrator sum. Responsive to the integrator sum exceeding a calibrated integrator threshold, the controller executes a control action, including automatically executing a Weather Mode in which energy use of the battery pack is reserved for traction control/propulsion of the vehicle.