This article mostly discusses longer-term forecasts, but I have also been impressed with the quality and reliability of imminent-storm alerts. They have saved me from getting drenched in a rain storm or allowed me to pull off the road for a break before a downpour.
It doesn't get a ton of press, but as this article highlights, progress has been steady and significant.
This article asserts that improving forecasts in low-income countries is underrated--does anyone know of studies that predict the impact better forecasts would have? Helping the poor with tech seems like the kind of project that many philanthropists could get excited about, and hopefully more effective than gravity lights and the like.