Per the Underground Utility Safety and Damage Prevention Act.

§ 87-117.  Definitions.
(11)  Extraordinary circumstances. - Circumstances that make it impossible for the operator to comply with the provisions of this Article, including hurricanes, tornadoes, floods, ice, snow, and acts of God.

§ 87-121.  Facility operator responsibilities.
(e)  If extraordinary circumstances prevent the operator from marking the location of the facilities within the time specified in subsection (b) of this section, the operator shall either notify the excavator directly or notify the excavator through the Notification Center. When providing the notification under this subsection, the operator shall state the date and time when the location will be marked.

§ 87-122.  Excavator responsibilities.

(5) If the operator declares extraordinary circumstances, the excavator shall not excavate or demolish until after the time and date that the operator has provided in the operator's response.