Rhône. After the heatwave, thunderstorms and heavy rain expected in Lyon

As the heatwave finally comes to an end in the Rhône, it is time to take stock and put things into perspective compared to its predecessors... And to prepare for the radical change in weather that begins this Tuesday, announcing a week where temperatures will, for once, be below seasonal norms.

The heatwave that began on the afternoon of Thursday, August 7, ended on Monday, August 18. In total, therefore, "11 days of intense heat," "well above seasonal norms," said a Météo France forecaster, interviewed by Le Progrès.

This is the 56th since the creation of the Lyon-Bron station in 1947, and it ranks 9th in terms of duration, the longest having lasted 17 days in July 2006.

In terms of temperatures, and despite two days spent on red alert (activated for the second time in the department, the first switch having taken place during the heatwave of 2023), no record was broken in Lyon, even if we came close, notably Saturday 9 (39 °C), Tuesday 12 (39.5 °C) and Wednesday 13 August (39.6 °C). The absolute heat peak ever recorded at the Lyon-Bron station remains that of 41.4 °C on August 24, 2023.

In the western Rhône, the commune of Sauvages still broke its temperature records, with a thermometer rising to 37.2 degrees on Tuesday, erasing the 36.5 degrees of July 31, 2020.

Météo France has nonetheless noted that these episodes of intense heat are becoming increasingly frequent, intense, and, above all, occurring early. This is an opportunity to recall the one at the end of June this year.

If the heatwave ends this Monday, August 18, a day notable for its lack of any warning whatsoever, Météo France has classified part of Tuesday, August 19, as a yellow alert for thunderstorms and rain-flooding. Between 1 p.m. and 6 p.m., the Lyon basin is expected to experience "high intensity" rainfall, with even a local risk of hail.

These storms, caused by a cold front, will cause a "significant cooling," so much so that after several days spent well above seasonal norms, the department will this time fall below. This may not be the case on Tuesday, when the mercury is expected to peak at 31°C, but from Wednesday to Sunday, maximum temperatures will not exceed 25°C.

In its final stretch, the Rhône should finally return to seasonal temperatures. A little late to correct averages that should prove well above the usual curves.