Millin et al. (2026) Analyzing Stratospheric and Tropical Contributions to the Subseasonal Forecasts of the December 2017 and January 2004 North American Cold Air Outbreaks

⚠️ Warning: This summary was generated from the abstract only, as the full text was not available.

Identification

• Journal: Journal of Climate
• Year: 2026
• Date: 2026-03-26
• Authors: Oliver T. Millin, Jason C. Furtado
• DOI: 10.1175/jcli-d-25-0420.1

Research Groups

Not explicitly stated in the provided abstract. The study utilizes the Community Earth System Model Version 2 (CESM2) with the Community Atmosphere Model Version 6 (CAM6), indicating a community-developed modeling framework.

Short Summary

This study investigates the individual roles of stratospheric and tropical variability in driving subseasonal cold air outbreak (CAO) forecast skill in the central United States using targeted nudging experiments. It finds that the impact of these modes on CAO prediction skill is event-dependent, with stratospheric nudging significantly improving forecasts for one event while both modes had limited surface impact for another.

Objective

• To assess the individual impact of stratospheric and tropical variability on subseasonal cold air outbreak (CAO) forecast skill in the central United States using targeted nudging experiments within the CESM2-CAM6 model.

Study Configuration

• Spatial Scale: Central United States, Canada, eastern United States, tropics, and the stratosphere (above 100 hPa).
• Temporal Scale: Subseasonal forecasts, initialized at various dates preceding two specific CAO events (December 2017/January 2018 and January 2004).

Methodology and Data

• Models used: Community Earth System Model Version 2 (CESM2) with the Community Atmosphere Model Version 6 (CAM6).
• Data sources: Reanalysis data (used for nudging the stratosphere and full tropical atmospheric column).

Main Results

• For the December 2017/January 2018 CAO event:
  • NUDGE-S (stratospheric nudging above 100 hPa) substantially improved forecasts of negative near-surface temperature anomalies across Canada and the eastern US and enhanced the forecast of key tropospheric regimes.
  • NUDGE-T (full tropical atmospheric column nudging) modestly improved temperature forecasts while strengthening the Alaskan ridge.
• For the January 2004 CAO event:
  • Both nudging approaches (NUDGE-S and NUDGE-T) had limited near-surface temperature impact, despite improving forecasts of winter weather regimes.
• Overall, the findings suggest that both tropical and stratospheric variability can influence CAO prediction skill, but their impacts are event-dependent.

Contributions

• Quantifies the event-dependent influence of stratospheric and tropical variability on subseasonal cold air outbreak forecast skill in the central US.
• Highlights the necessity for a better understanding of the specific conditions and mechanisms through which stratospheric and tropical modes contribute to surface extreme events for improved subseasonal prediction.

Funding

Not specified in the provided abstract.

Citation

@article{Millin2026Analyzing,
  author = {Millin, Oliver T. and Furtado, Jason C.},
  title = {Analyzing Stratospheric and Tropical Contributions to the Subseasonal Forecasts of the December 2017 and January 2004 North American Cold Air Outbreaks},
  journal = {Journal of Climate},
  year = {2026},
  doi = {10.1175/jcli-d-25-0420.1},
  url = {https://doi.org/10.1175/jcli-d-25-0420.1}
}