Forecasts have improved dramatically. A 7-day forecast is now somewhat useful when deciding to have your party indoors or outdoors, whereas in the 90s next-day

Forecasts have improved dramatically. A 7-day forecast is now somewhat useful when deciding to have your party indoors or outdoors, whereas in the 90s next-day forecasts could hardly compete with the naive assumption of "the weather will stay as it is". But by mentioning machine learning, I'm guessing you are looking at a different timescale, i. e. "within the last two years". And any progress in the short term will be slow compared to what we have seen in other domains such as image recognition etc. I'm no expert on weather forecasting, but I believe the explanation may be that forecasts have long been (among the) best financed "big data" problems out there. That means they incorporate lots and lots of domain-specific work. As a result, naive machine learning models currently still lag all the specialised work, which in turn isn't structured in a way to easily take advantage of progress in, say, GPUs.