National Integrated Drought Information System Reauthorization Act of 2018 This bill reauthorizes through FY2023 and modifies the National Integrated Drought Information System (NIDIS) Program. The bill amends the National Integrated Drought Information System Act of 2006 to require, under NIDIS, that the collection and integration of information on the key indicators of drought and drought impacts includes indicators of precipitation, soil moisture, and evaporative demand. NIDIS shall also: provide timely data, information, and products that reflect watershed differences in drought conditions; through interagency agreements, coordinate and integrate future federal research and monitoring in support of a drought early warning information system; utilize existing forecasting and assessment programs and partnerships, including forecast communication coordinators and cooperative institutes, and improvements in seasonal, subseasonal, and low flow water prediction; and continue ongoing research and monitoring activities related to drought, including research activities relating to the prediction of drought. NIDIS may: engage with the private sector to improve drought forecast and communication if the National Oceanic and Atmospheric Administration determines such partnership is appropriate, cost-effective, and beneficial to the public and the decision-makers specified in the Act; and facilitate the development of one or more academic cooperative partnerships to assist with NIDIS functions. NIDIS shall develop a strategy for a national coordinated soil moisture monitoring network. The bill amends the Food Security Act of 1985 to extend through FY2023 certain activities related to the provision of agricultural and silvicultural weather and climate information.