Forecast for the next few hours: 100mm+ possible locally!


Bulletin of September 14, 2022 at 09:00 – A moderately dynamic depression is currently located 200 km from Galicia and Portugal. It extends through a much more extensive low pressure thalweg, which rises to the British Isles. At the same time, the anticyclone is pushed back towards Italy. The flow at altitude is curved in the southwest sector while on the ground it is oriented to the southeast. This is one aspect that differs from the previous situations: for this episode we have a more dynamic low-altitude jet than during the previous episodes. A first stormy salvo circulated in the early 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 calm is formed. The clouds are numerous. The southeast wind (low-level jet) will strengthen over the Camargue and the Crau, with gusts of 50 and 70 km/h at noon. In this context, air saturated with water and instability rises from the Mediterranean. PWAT (precipitable water) content will exceed 50 mm today between the east of Hérault and Gard. This is very significant: Timeline: Showers restart before 10am this morning inland in Hérault and Gard, approaching the Cévennes. Sometimes they are loud, but they seem to circulate. 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 convergence in the lower layers. In this context, we bet on the establishment of a SMALL MOBILE stormy system between the end of the morning and midday, with the highest probability between the east of the Hérault and the Gard plains. In connection with a stronger offshore wind than in previous episodes, the storm axis is likely to be located “further” inland than during recent events. It will be a linear system, stretched from SW to NE, with a tendency to regenerate in place (possibility of retrograde initiation, or temporary stationarity). As always, it is difficult to perfectly locate this storm axis. 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! The Arôme fine-resolution model illustrates this risk well (the location should not be taken literally): this stormy risk persists until mid-afternoon over eastern Hérault, but until late afternoon in the Gard. Storms will move out of the region through the Rhone Valley later in the day. In general, this degradation of ordinary fall requires special attention, due to a LOCALIZED risk of strong phenomena. It is not exceptional. We can observe, under these stormy lines, accumulations of 50 to 60 mm in 1 hour and up to 100 mm in 2 hours or 150 mm very isolated in 3 hours. It is significant. A few hail storms are also possible, caution. It should be borne in mind that for most municipalities, the accumulations will remain significantly lower. However, if these violent storms affect agglomerations, this may induce low-lying flooding and/or a temporary risk of heavy runoff. The municipalities around Nîmes are particularly at risk of intense runoff. Situation to follow live with Météo Languedoc.
#Forecast #hours #100mm #locally


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