Impact of synoptic circulation types on power system imbalance forecast errors in Sweden

The share of weather-dependent renewable energy is rising as European power grid balancing markets move toward greater unification. In the Nordics, proactive and automatic balancing using manual Frequency Restoration Reserves was implemented in March 2025, a prerequisite for joining the European balancing platform Manually Activated Reserves Initiative. This paper investigates data from Sweden following its automatic balancing implementation to determine if the challenge of maintaining grid stability correlates with synoptic circulation types. For this study, the challenge of maintaining grid stability is quantified by the absolute error of the imbalance forecast algorithm within the new system. Circulation types are computed using the automatic Jenkinson-Collison classification scheme based on atmospheric surface pressure signals. A regression analysis establishes circulation types as a statistically significant driver of absolute imbalance forecast errors and reveals that balancing is more challenging under cyclonic flows and those originating from the north-westerly quadrant. A control study highlights wind speed as the most dominant underlying parameter. However, accounting for wind speed does not remove all influence of the circulation types, demonstrating that they act as a proxy for complex weather dynamics that affect imbalance forecasting.