Weather warning: Snow and heavy rain in the southwest
Of for
The situation
In the general northwesterly flow, a wintry and very disturbed, new very active trough from the Bay of Biscay moves across southwestern France on Thursday. It produces heavy precipitation and snow falls on the plain from late afternoon to late night as the air mass cools significantly. New significant rain accumulation is expected in Landes and Pyrénées-Atlantiques with a blocking effect. In addition to those recorded since Sunday, this deterioration increases the risk of flooding on many rivers. In a very unstable context, strong winds again hit the coast of Aquitaine before crossing the foothills of the Pyrenees and then moving towards the Mediterranean Sea.
Observation
at 9 p.m., the depression descends to the east of the Pyrenees massif and with it the temperatures. It is snowing from Dordogne to Aveyron. In Bergerac and Périgueux, the layer reaches 5 cm on the ground. Snow begins to fall in Montauban, Gourdon and Albi. Further south, it rains, but in cities like Toulouse, Carcassonne and Béziers, snow quickly replaces the rain. In the Pyrenees, the rain-snow limit is about 800 meters
At 6 p.m, snow replaced rain in the Charentes and Dordogne plains. 1 cm bleaches the observed soils in the Cognac region. The soils are also beginning to turn white in Périgord. It rains further south, but snow will eventually replace the rain north of the Garonne in towns like Montauban, Gourdon, Albi. Snow begins to fall in Cantal and Aveyron. In the Pyrenees, the rain-snow limit is close to 800 meters.
At 3 p.m, as in Limoges, a temperature drop of up to 1 degree turned the rain into snow, mostly between Limousin and the north of the Tarn department. It always rains on the coast of the Atlantic Ocean. Snowfall is more persistent in the transition zone between the two regions, southwest of Limoges in Corrèze.
at 12: Precipitation is intensifying over the Aquitaine basin and the rain/snow limit continues to rise above 600-800 meters. In the Basque country, the intensity reaches an average of 2 to 4 mm/h. Under the influence of ocean currents, the temperature rises slowly, varying between 3 and 6°C. Cold weather resists in the departments of Tarn, Aveyron, Lot and Tarn-et-Garonne with average temperatures between 0 and 4°C.
At 9 o’clock: Rainfall is fairly low and infrequent over the Aquitaine basin, with an average of 300 to 400 m of snow. Temperatures in departments under snow yellow warning are between 2 and 6°C with melting from the Atlantic Ocean, and in departments with snow orange -2 to 5°C (on the coast).
Evolution
Tonight : an improvement north of the Garonne with the cessation of snow, but a deterioration east of the Pyrenees before continued snow down to the Languedoc coastal plain. Stormy winds in the mountains will produce significant snowpacks as far as Andorra.
Friday
A rapid and significant increase in pressure associated with the return of anticyclonic conditions will contribute to a general improvement and an end to snow in the eastern Pyrenees in the morning.
During this episode we expect:
– In the north of the Landes and Pyrenees-Atlantiques, an average of 30-40 mm of precipitation, and up to 70 mm in the foothills of the Pyrenees.
– possible snowfall up to the plains due to isothermal effect with the risk of snow cover thickness from 300 m to 1 to 5 cm and from 500 m to 5 to 10 cm in the orange alert sections. Accumulations may exceed 20 cm above 800 m.
– Strong winds with a speed of 100-120 km/h on the Landes coast to the Basque coast, and 80-90 km/h near the foothills of the Pyrenees.
– Wide risk of flooding between Landes and P. Atlantiques, after 120 to 160 mm have already been recorded in several sectors. This will bring the total cumulative rainfall locally to around 250mm since Sunday, or 1 to 3 weeks of rain.
