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© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  28 Sep 2020

28 Sep 2020

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This preprint is currently under review for the journal NHESS.

The heavy precipitation event of 14–15 October 2018 in the Aude catchment: A meteorological study based on operational numerical weather prediction systems and standard and personal observations

Olivier Caumont1, Marc Mandement1, François Bouttier1, Judith Eeckman1,2, Cindy Lebeaupin Brossier1, Alexane Lovat1,3, Olivier Nuissier1, and Olivier Laurantin3 Olivier Caumont et al.
  • 1CNRM, Université de Toulouse, Météo-France, CNRS, Toulouse, France
  • 2IMFT, Université de Toulouse, CNRS, Toulouse, France
  • 3Observing Systems Division, Météo-France, Toulouse, France

Abstract. The case of the heavy precipitation event on 14 and 15 October 2018 which has led to severe flash flooding in the Aude watershed in south-western France is studied from a meteorological point of view using deterministic and probabilistic numerical weather prediction systems, as well as a unique combination of observations from both standard and personal weather stations. This case is typical of Mediterranean heavy precipitation events due to its classic synoptic situation and its quasi-stationary convective precipitation that regenerates continuously, but with some peculiarities such as the presence of a former hurricane and a pre-existing cold air mass close to the ground.

It is shown that the positive Mediterranean sea surface temperature anomaly may have played an aggravating role in the amount of precipitation that poured into the Aude basin. On the other hand, soil moisture does not seem to have played a significant role. A study of rainfall forecasts shows that the event had limited predictability, in particular given the small size of the watersheds involved. It is shown that the stationarity of precipitation, whose estimation benefits from data from personal stations, is linked to the presence near the ground of a trough and a strong potential virtual temperature gradient, the stationarity of both of which is highlighted by a combination of observations from standard and personal stations. The forecast that comes closest to the rainfall observations contains the warmest, wettest and fastest low-level jet and also simulates near the ground a trough and a marked boundary between cold air in the west and warm air in the east, both of which are stationary.

Olivier Caumont et al.

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Olivier Caumont et al.

Olivier Caumont et al.


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Short summary
This study focuses on the case of the heavy rainfall of 14 and 15 October 2018, which caused deadly flash floods in the Aude basin in south-western France. Although similar to the heavy rainfall events that regularly affect the Mediterranean Sea, it is shown, using operational forecasting models and observations including personal observation data, that this case presented specific aggravating factors near the ground.
This study focuses on the case of the heavy rainfall of 14 and 15 October 2018, which caused...