Finally a rainfall paper that perhaps you can believe in!?:
We test whether earlier social distancing affects the progression of a local COVID-19 out-break. We exploit county-level rainfall on the last weekend before statewide lockdown. After controlling for state fixed-effects, temperature, and historical rainfall, current rainfall is a plausibly exogenous instrument for social distancing. Early distancing causes a reduction in cases and deaths that persists for weeks. The effect is driven by a reduction in the chance of a very large outbreak. The result suggests early distancing may have sizable returns, and that random events early in an outbreak can have persistent effects on its course.