Disconnect the microwave from the power source while the power is still out. If the microwave is a built-in, turn off the circuit breaker. Otherwise, unplug the microwave from the wall outlet. This prevents a power surge from damaging the magnetron tube when the power is restored.
Turn on the circuit breaker or plug the microwave into the outlet only when you are sure that the power is permanently restored. If there are still storms in the area, the power may be disrupted again.
Reset the clock on the microwave. Microwaves vary slightly on how to set the clock, but usually there is a clock button you press. Use the number pad to input the correct time and press the clock button again to set it.
Test the microwave by heating some water to ensure that it is still in good operating condition.