Hail storms are alarming. Hail anywhere that’s big enough – even reaching 8” diameter, bigger than a regulation softball – damages houses and cars and harms or even kills crops, livestock, wildlife, and humans.
Hail needs special conditions to form, fortunately. All precipitation as rain, snow, or hail forms in clouds with repetitious circulation of droplets or ice particles up and down, gathering mass and size. It starts with tiny bits of dust, salt, or other solids that allow the first condensation of water. Hail forms if clouds have strong updrafts to keep cycling the growing ice particles and the clouds grow high enough to very cold areas.
In Europe, a perhaps surprising source for nucleation is dust from the Sahara. Killian Brennan and Lena Willhelm in Switzerland related satellite measurements of dust parcels with weather records. Hail days had nearly twice the average dust levels and mostly came from the Sahara. If there can be an optimum for dust levels, that’s it. Even higher dust levels don’t support hail; there are too many nucleation sites competing with each other for the group to all grow big.
These “Saharan” hail storms especially hit France, Germany, and Austria but hit other areas. A super-dry area brings unwelcome precipitation!
This has been an outreach activity of the Las Cruces Academy, viewable at GreatSchools.org
Source: Nature, 9 October 2025, p. 262, reporting a story in Atmospheric Chemistry and Physics
Image: Same
