Preprints
https://doi.org/10.5194/wcd-2021-32
https://doi.org/10.5194/wcd-2021-32

  10 Jun 2021

10 Jun 2021

Review status: this preprint is currently under review for the journal WCD.

Flow dependence of wintertime subseasonal prediction skill over Europe

Constantin Ardilouze1, Damien Specq1, Lauriane Batté1, and Christophe Cassou2 Constantin Ardilouze et al.
  • 1CNRM, Université de Toulouse, Météo-France, CNRS, Toulouse, France
  • 2CECI, Université de Toulouse, CNRS, CERFACS, Toulouse, France

Abstract. Issuing skillful forecasts beyond the typical horizon of weather predictability remains a challenge actively addressed by the scientific community. This study evaluates winter subseasonal reforecasts delivered by the CNRM and ECMWF dynamical systems and identifies that the level of skill for predicting temperature in Europe varies fairly consistently in both systems. In particular, forecasts initialized during positive North-Atlantic Oscillation (NAO) phases tend to be more skillful over Europe at week 3 in both systems. Composite analyses performed in an atmospheric reanalysis, a long-term climate simulation and both forecast systems unveil very similar temperature and sea-level pressure patterns three weeks after NAO conditions. Furthermore, regressing these fields onto the 3-week prior NAO index in a reanalysis shows consistent patterns over Europe but also other regions of the northern hemisphere extratropics, thereby suggesting a lagged teleconnection, either related to the persistence or recurrence of the postive and negative phases of the NAO. This teleconnection, conditionned to the intensity of the initial NAO phase, is well captured by forecast systems. As a result, it is a key mechanism for determining a priori confidence in the skill of wintertime subseasonal forecasts over Europe as well as others parts of the northern hemisphere.

Constantin Ardilouze et al.

Status: open (until 22 Jul 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse

Constantin Ardilouze et al.

Constantin Ardilouze et al.

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Short summary
Forecasting temperature patterns beyond two-weeks is very challenging although occasionally, forecasts show more skill over Europe. Our study indicates that the level of skill varies concurrently for two distinct forecast systems. It also shows that higher skill occurs when forecasts are issued during specific patterns of atmospheric circulation that tend to be particularly persistent. These results could help forecasters estimate ‘a priori’ how trustworthy extended-range forecasts will be.