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The storm was in the eastern French Pyrenees. This region is no stranger to hail — the Pyrenees is a well-known hail hotspot. This map shows where we get the most frequent hail environments in Europe (www.nature.com/articles/s41... CC-BY-4.0). 2/14

The hailstorm hit when the riders were 15 km from the stage finish, cycling through Mont-Louis, at about 17:30 CEST (15:30 UTC). Radar data at that time show high reflectivities (over 50 dBZ) indicating the presence of large particles and lots of rain (zoom.earth/maps/radar/#...). 3/14

Some protruding clouds appear in satellite imagery at that time, likely developed by strong updrafts that can support hail growth (MTG GeoColour RGB with MSG IR10.8 in the background, view.eumetsat.int). 4/14

Hailstorms are small in scale, so it’s hard to forecast or model exactly where and when hail will happen. But we can consider whether the atmosphere is more or less likely to produce hail. 5/14

27/8/26, 6:36 am0 reposts1 like

We often consider the atmospheric “ingredients” for hail. Two common ones are instability (propensity for updrafts to form) and wind shear (difference in wind by height). If you have lots of instability and wind shear together, hail is more likely and the environment is “hail-prone”. 6/14

So was there instability and wind shear in this case? Yes, at least in the vicinity, in a model forecast (adapted from charts.ecmwf.int, CC-BY-4.0). 7/14

The European Severe Storms Laboratory’s more sophisticated forecast also showed probabilities of up to 60% for large hail, in regions around where the hail occurred (www.stormforecast.eu). 8/14