Huang et al. (2026) Why Do Extended‐Range Forecasts Underpredict the Extreme Negative Pacific/North American Pattern in February 2018?

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

Identification

• Journal: Journal of Geophysical Research Atmospheres
• Year: 2026
• Date: 2026-04-04
• Authors: Jinlong Huang, Peter Hitchcock, Wenshou Tian, Q. X. Li, Li He
• DOI: 10.1029/2025jd045964

Research Groups

Not explicitly stated in the abstract, but the study utilizes the Stratospheric Nudging and Predictable Surface Impacts (SNAPSI) multi-model ensemble and models from the Subseasonal-to-Seasonal (S2S) prediction project database, implying collaboration across multiple climate modeling centers.

Short Summary

This study investigates the failure of extended-range forecasts to capture the extreme negative Pacific/North American (PNA) event of February 2018, attributing the error to an underestimation of the East Asian trough, biases in sea surface temperatures, and complex, initialization-dependent stratospheric-tropospheric coupling.

Objective

• To investigate the reasons behind the notable failure of extended-range forecasts to capture the extreme negative PNA event of February 2018, using a novel multi-model ensemble designed to isolate stratospheric sources of predictability.

Study Configuration

• Spatial Scale: Mid-latitudes, North America, East Asia, North Pacific, Arctic (Northern Hemisphere focus).
• Temporal Scale: Extended-range (subseasonal-to-seasonal), focusing on a specific event in February 2018 and its precursors over preceding weeks and months.

Methodology and Data

• Models used: Stratospheric Nudging and Predictable Surface Impacts (SNAPSI) multi-model ensemble; models from the Subseasonal-to-Seasonal (S2S) prediction project database.
• Data sources: Model outputs and forecast errors from the SNAPSI multi-model ensemble and S2S project database.

Main Results

• The forecast error for the February 2018 negative PNA event stemmed from an underestimation of several key atmospheric processes.
• The primary bottleneck was the poor simulation of the East Asian trough (EAT), a well-established upstream precursor; models that better represented the EAT produced more accurate PNA forecasts.
• Biases in both tropical (La Niña) and extratropical North Pacific sea surface temperatures (SSTs) also contributed to the PNA forecast bias.
• The Madden-Julian Oscillation (MJO) had limited direct influence within the SNAPSI forecasts, but supplementary analysis showed its accurate simulation in earlier weeks was critical for EAT development based on S2S models.
• The stratospheric contribution was initialization-dependent:
  • For a late-January forecast, the tropospheric response to the February 2018 sudden stratospheric warming (SSW) varied widely among models, limiting its net effect on the PNA.
  • For a February initialization, most models produced an excessive negative Arctic Oscillation (AO) response, which amplified a positive PNA bias.

Contributions

• Provides a detailed diagnosis of a specific, significant extended-range forecast failure (February 2018 PNA event) using a novel multi-model ensemble (SNAPSI).
• Highlights the complex interplay of mid-latitude wave dynamics (East Asian trough), tropical-extratropical linkages (SST biases, MJO), and stratosphere-troposphere coupling in subseasonal-to-seasonal predictability.
• Identifies specific priorities for improving extended-range predictions: better representation of mid-latitude wave dynamics, refinement of stratosphere-troposphere coupling, and improved integration of tropical-extratropical linkages.

Funding

Not explicitly stated in the abstract.

Citation

@article{Huang2026Why,
  author = {Huang, Jinlong and Hitchcock, Peter and Tian, Wenshou and Li, Q. X. and He, Li},
  title = {Why Do Extended‐Range Forecasts Underpredict the Extreme Negative Pacific/North American Pattern in February 2018?},
  journal = {Journal of Geophysical Research Atmospheres},
  year = {2026},
  doi = {10.1029/2025jd045964},
  url = {https://doi.org/10.1029/2025jd045964}
}