more than 100 mm possible locally!

more than 100 mm possible locally!

more than 100 mm possible locally!

Bulletin of September 14, 2022 09:00 am – A moderately dynamic depression is currently located 200 km off the coast of Galicia and Portugal. It is extended by a much larger low-pressure thalweg, which goes up to the British Isles. At the same time, the anticyclone is pushed back towards Italy. The flow at high altitude is curved towards the South-West sector while on the ground it is oriented towards the South-East. This is one of the aspects that differs from the previous situations: we have for this episode a more dynamic low-level jet compared to previous episodes.

A stormy first salvo rolled early in the morning east of Hérault and Gard. It gave good rains, saving nature, with a maximum of 20/30 mm in the most affected areas but often much less. During the morning, a relative truce is formed. The clouds are numerous. The south-east wind (low-altitude jet) will strengthen on the Camargue and La Crau, with gusts from 50 to 70 km / h by noon. In this context, air saturated with water and instability rises from the Mediterranean. PWAT content (precipitable water) will exceed 50 mm today between the eastern Hérault and the Gard. It is very significant:

Chronology: the showers resume before 10 am this morning in the hinterland of Hérault and Gard, approaching the Cévennes. Sometimes they are strong, but they seem to be circular. At the end of the morning, the air mass becomes increasingly unstable, with MUCAPE values> 1500 or 2000 J / kg over eastern Hérault and Gard. This fuel will increase stormy convection, in phase with the convergence in the lower strata. In this context, we are betting on the establishment of a stormy system SMALL MOBILE between late morning and midday, with a maximum probability between the eastern Hérault and the Gard plain.

In connection with a stronger sea wind than in previous episodes, the storm axis is likely to be “more” inland than in recent events. It will be a linear system, extending from SW to NE, with a tendency to regenerate on the spot (possibility of retrograde onset, or temporary stationarity). As always, this stormy axis is difficult to locate perfectly. The most exposed areas are between Montpellier, Lunel, Pic Saint-Loup, Vidourle, Gardonnenque, Vaunage, the plain of Nîmes, the Uzège basin and perhaps even near the Rhone. This will be monitored in real time! Arôme’s fine resolution model is a good example of this risk (position not to be taken literally):

This stormy risk persists until mid-afternoon in eastern Hérault, but until late afternoon on the Gard. Storms will leave the region via the Rhone Valley at the end of the day. In general, this ordinary autumn decay requires special attention, due to a LOCALIZED risk of strong phenomena. It is not great. Accumulations of From 50 to 60 mm in 1 hour and up to 100 mm in 2 hours or 150 mm highly insulated in 3 hours. It’s significant. Some hailstorms are also possible, be careful.

It should be noted that for most municipalities the accumulations will remain considerably lower. However, if these violent storms hit the agglomerations, this can cause flooding in low points and / or a temporary risk of strong outflow. The municipalities around Nîmes are particularly at risk of intense flow. Situation to follow live with Météo Languedoc.

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