Modelling Freeze Hazard for the North American Winters

Freeze hazard represents the costliest peril associated with winter weather in the United States (US). This study focuses on the development and validation of a Freeze Index (FI) to model the impact of freeze effectively. The FI integrates both the intensity and duration of freeze events, offering a more accurate modelling of freeze hazards. The updated FI is used to select US-wide events targeting mainly the spatial scale of cold air outbreaks (CAOs). Validation of the hazard footprints is performed against historical data, including the December 2022 CAO and the Texas freeze of 2021. The findings underscore the importance of considering both temperature and duration in freeze hazards to model the damages accurately.

The freeze events obtained above are used to investigate trends in duration and FI, using 2-metre temperature (T2M) from the reanalysis data (1950 – 2024) and compared with the events from the detrended T2M. In the detrended set, no significant trend is observed in the duration of events from 1950 onwards. The average FI obtained from the footprints of each event also did not show a significant trend. The freeze events obtained from the non-detrended T2M also do not show a significant trend in duration and average FI for the events. However, there is a clear decrease in the occurrence of long-duration events with only four events greater than 10 days from 1990 onwards compared to thirteen events in the 1950 – 1985 period.