I think the bigger issue is the update frequency. My weather app updates minute-by-minute, giving me essentially real-time precipitation information from my neighbourhood weather station. If each future time is a column, you're looking at 60 columns just for the next hour of forecast. It really adds up!

This level of detailed information can't be pre-cached, either. I believe they are feeding the real-time weather recordings from the weather station into their supercomputer model to generate minute-by-minute high resolution forecasts over the next 6 hours.