Ensuring stable power supply and proper electric power quality while continuously managing the production, transmission and distribution of electricity is the main goal of the dispatch center of any power system, including an isolated one. Continuous management is based on an electric power regime planning process. According to its results, the dispatch center sends to the electric power industry entity the planned dispatch schedule of the power generation, transmission and consumption in an hourly (half-hour) breakdown, which has to be received by the managed entity 8-10 hours before the onset of the planned day. In the operational management of the electric power regime, the dispatch center operators on duty adjust (update) the values of the planned dispatch schedule. Active power consumption in the power system is one of the most significant parameters being updated. The possibilities of improving the accuracy of operationally forecasting active power in isolated power systems are investigated taking the Kaliningrad power system as an example. The existing power consumption forecasting methods are analyzed. The influence of power plant auxiliaries on the total active power consumption in the power system is studied. Methodological principles for operational forecasting of power consumption have been developed and proposed, which are recommended for inclusion in regulatory documents as a methodology. The proposed methodology is based on a mathematical model that takes into account the consumed power variation rate on a typical day, forecasted meteorological data and the dependence of power consumption for power plant auxiliaries on the composition of the generating equipment switched in operation.