Weather warning: Snow and heavy rain in the southwest
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Situation
In general a northwesterly current, cool and very disturbed, a new very active depression came up from the Bay of Biscay across southwest France on Thursday. This results in heavy rainfall and, with a pronounced cooling of the air masses, snowfall onto the plains between the evening and the following night. With the blocking effect, significant accumulation of new rain is expected in the Landes and Pyrénées-Atlantiques. Adding to those recorded since Sunday, this worsening increases the risk of flooding in many rivers. In an extremely unstable context, strong winds hit the Aquitaine coast again before crossing the Pyrenean foothills and then moving towards the Mediterranean.
Observation
At 21 hours, the depression plunges eastward into the Pyrenean mountains, and with it the temperature. It snows from the Dordogne to Aveyron. In Bergerac and Périgueux, the layer is up to 5 cm above the ground. Snow is starting to fall on Montauban, Gourdon and Albi. Further south it rained, but snow quickly replaced rain in cities such as Toulouse, Carcassonne and Béziers. In the Pyrenees, the rain-snow boundary is about 800 meters
18 o’clock, snow replaces rain on the plains of the Charentes and Dordogne. It bleached the soil in the Cognac region by 1 cm observed. The ground also started to turn white in Périgord. Further south, it rains, but snow will eventually replace rain north of Garonne, in cities like Montauban, Gourdon, Albi. Snowfall begins on Cantal and Aveyron. In the Pyrenees, the rain-snow boundary is about 800 meters.
15 o’clock, a drop in temperature of up to 1 degree, as in Limoges, most often turns rain into snow between Limousin and the northern department of Tarn. On the Atlantic coast, it always rains that predominate. Between the two areas, in the transition zone that runs southwest of Limoges in Corrèze, snowfall is more persistent.
At 12 o’clock : rain intensified over the Aquitaine basin and the rain/snow limit continued to increase, beyond 600 to 800 meters. The average intensity is 2 to 4 mm/hour in the Basque Country. The temperature rises gradually, under the influence of ocean currents, by 3 to 6°C. Holds cold in the Tarn, Aveyron, Lot and Tarn-et-Garonne departments with average temperatures varying from 0 to 4°C.
At 9 o’clock : it rains fairly lightly and infrequently over the Aquitaine basin and snowfalls average from 300 to 400 m. Temperatures in the yellow warning department are around 2 to 6°C with thaw coming off the Atlantic and -2 to 5°C (on the coast) in the orange snow department.
Evolution
Tonight : it is increasing north of the Garonne with the cessation of snowfall, but worsening east of the Pyrenees before the snowfall settles down to the coastal plains of the Languedoc. In the mountains, storm winds will build significant snow drifts as far as Andorra.
Friday
A rapid and significant increase in pressure, associated with a return to anticyclonic conditions, will favor general improvement and an end to the early morning snowfall in the eastern Pyrenees.
During this episode, we expect:
– Rainfall averages 30 to 40 mm in the Landes and north of the Pyrénées-Atlantiques, and up to 70 mm in the Pyrenean foothills.
– possible snowfall as far as the plains due to isothermal effects, with a risk of snow cover thickness of 1 to 5 cm from 300 m in the department placed in orange alert and from 5 to 10 cm from 500 m. Accumulation can exceed 20 cm over 800 m.
– strong wind gusts of 100 to 120 km/h on the Landes coast to the Basque coast and 80 to 90 km/h near the Pyrenean foothills.
– risk of widespread flooding between the Landes and P. Atlantiques, after 120 to 160 mm has been recorded in some sectors. This will bring the total cumulative rainfall since Sunday to nearly 250 mm locally, or 1 month to 3 weeks of rain.
