Source: Harvard University (https://projects.iq.harvard.edu/covid19)
The visualization above show how reproductive number is impacted by weather in each location, captured in the Relative COVID-19 Risk due to Weather (CRW). CRW compares the relative changes in reproductive number for the disease due to weather factors. For example, a shift over a season in CRW from 1 (the 90 percentile in sample) to 0.7 in a given location points to 30% reduction in estimated reproduction number over that period due to weather (i.e. assuming everything else is constant).