Dynamics of forecast-error growth along cut-off Sanchez and its consequence for the prediction of a high-impact weather event over southern France ...

• Main Authors: Binder, Hanin, Rivière, Gwendal, Arbogast, Philippe, Maynard, Karine, Bosser, Pierre, Joly, Bruno, Labadie, Carole
• Format: Text
• Language: English
• Published: ETH Zurich 2021
• Subjects: diabatic processes; dynamics; forecast sensitivity; high-impact weather; humidity; NAWDEX; numerical weather prediction; North Atlantic
• Online Access: https://dx.doi.org/10.3929/ethz-b-000502757; http://hdl.handle.net/20.500.11850/502757

The representation of a high-impact weather (HIW) event over southern France is evaluated in Meteo-France forecasts, and the sensitivity of the HIW forecast to the upstream upper-level flow and the Mediterranean and North Atlantic humidity structure prior to the event is quantified. The event occurred in October 2016 during the international field experiment NAWDEX. The approach of an upper-level potential vorticity (PV) cut-off, referred to as cut-off Sanchez, triggered extreme precipitation over southern France. Many 2- to 7-day ensemble forecasts predicted the maximum of the extreme precipitation and the location of the upper-level PV cut-off too far to the east. This eastward shift primarily resulted from an underestimation of the cut-off intensity two days before the HIW and the subsequent downstream propagation and amplification of these errors in the vicinity of Sanchez. Improving the representation of the cut-off two days before the event significantly improved the forecast quality. Another error ... : Quarterly Journal of the Royal Meteorological Society, 147 (739) ...