As many media outlets recently reported, the Mexican city of Guadalajara woke up on Sunday, 30 June 2019, to more than one meter (~3 feet) of hail in some areas. At least one report indicates hail up to two meters deep! Vehicles were swept away and nearly 200 homes and businesses reported hail damage. All this while the region had been experiencing summer temperatures of up to 31°C (88°F) in recent days. As shown in Figures 1 and 2 below, the hail was indeed quite deep. Civil protection personnel and soldiers with heavy machinery were called in to help clear the roads. (News coverage: CNN, Aljazeera, and elsewhere.)

Figure 1: A truck buried in ice after a heavy storm of rain and hail which affected some areas of the city. (Fernando Carranza/Reuters; from Aljazeera)
Figure 2: Vehicles buried in hail are seen in the streets in the eastern area of Guadalajara. (Ulises Ruiz/AFP; from Aljazeera)

However, caution is needed in interpreting these stories. There is no doubt that the pictures are real and that this was an extraordinary event. But look closely at the aerial view in Figure 3. The very deep hail is concentrated mostly on one street and not on the rooftops. Cars on one street are turned and almost piled on each other. Cars parked a short distance away seem to be unaffected. It is therefore most likely that the large hail drifts were created by flash flooding down the streets, not by hail alone. In fact, it’s highly unlikely that a single storm event would have enough water in the vertical column and enough vertical force to form two meters of solid ice. Instead, the storms probably produced flooding and what some have referred to as “hail glaciers.”

Figure 3: An aerial view of the area where hail trapped cars and truck in the streets. (Ulises Ruiz/AFP; from Aljazeera)

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