Cumulonimbus builds software that collects and disseminates atmospheric pressure data from Android smartphones. We are collaborating with atmospheric scientists to use the data in new weather forecasting systems aimed at improving short-term severe weather forecasts. Our network has 12,000 active users and is receiving 300,000 measurements per day. We are building new services for data collection, assimilation and analysis in order to research and build the most modern and capable weather forecasting system to date.