Waymo, the Alphabet company that aims to deploy fleets of robotaxis all over the country, has been quietly investing in weather research since its early days as a “moonshot” project out of Google’s X division. And while its autonomous vehicles still struggled to navigate certain inclement conditions, the company has gotten a lot better at detecting and predicting the weather in the cities in which it operates — even creating a first-of-its-kind fog map for San Francisco.

The map is a product of millions of data points collected by Waymo’s fleet of autonomous vehicles as they traverse San Francisco’s fog-drenched streets. Combined with special weather-detecting vehicles equipped with visibility sensors, Waymo is able to create a new meteorological “metric” that it then feeds to its autonomous “Waymo Driver” to aid its decision-making.