Assessment of Ionospheric Model Performance Over the US During the Extreme G5 2024 Mother's Day Geomagnetic Storm

This study evaluates 17 ionospheric models' performance over the Continental United States (CONUS) during the 2024 Mother's Day geomagnetic storm, using ground‐based GNSS Total Electron Content (TEC) and single‐frequency (SF) precise Single Point Positioning (SPP) technique. The storm produced significant positive storm effects during its main phase and notable TEC depletions during recovery phases. We evaluate each model's capability to (a) reproduce vertical TEC magnitudes and spatiotemporal patterns, (b) capture storm‐driven TEC anomalies, and (c) support practical SF GNSS positioning. Data assimilation (DA) models, specifically GloTEC and GIS, show the best performance in representing the TEC magnitude, morphology and variability, and they yield the lowest positioning errors. Physics‐based models exhibit mixed performance. They better capture negative storm effects but generally underestimate positive TEC enhancements, likely due to the underestimation or absence of penetration electric field. Empirical models struggle to represent the storm‐time dynamics, although IRI2020 partially captured the recovery‐phase TEC depletions. SF GNSS SPP results suggest that scientific models provide more realistic ionospheric representations than the Klobuchar model during storm conditions. However, large systematic biases during the main phase can still introduce significant positioning errors. This work establishes a performance baseline for ionospheric models under extreme conditions and demonstrates their readiness for practical application. The validation results are integrated into the CCMC Ionosphere‐Thermosphere Model Assessment and validation Platform (ITMAP), supporting community‐wide benchmarking and future model development.