Introduction – Acme Weather Introducing Acme Weather Adam Grossman February 16, 2026 Fifteen years ago, we started work on the Dark Sky weather app. Over the years it went through numerous iterations — including more than one major redesign — as we worked our way through the process of learning what makes a great weather app. Eventually, in time, it was acquired by Apple, where the forecast and some core features were incorporated into Apple Weather. We enjoyed our time at Apple. So why did we leave to start another weather company? It’s simple: when looking at the landscape of the countless weather apps out there, many of them lovely, we found ourselves feeling unsatisfied. The more we spoke to friends and family, the more we heard that many of them did too. And, of course, we missed those days as a small scrappy shop. So let’s try this again… Embracing Uncertainty Our biggest pet peeve with most weather apps is how they deal (or rather, don’t deal) with forecast uncertainty. It is a simple fact that no weather forecast will ever be 100% reliable: the weather is moody, fickle, and chaotic. Forecasts are often wrong. Understanding this uncertainty is crucial for planning your day. Most weather apps will give you their single best guess, leaving you to wonder how sure they actually are, and what else might happen instead. Will it actually start raining at 9am, or might it end up pushed off until noon? Will there be rain or snow? How sure are you? You can’t plan your day if you don’t know how much you can trust the forecast, or know what other possibilities might arise. Rather than pretending we will always be right, Acme Weather embraces the idea that our forecast will sometimes be wrong. We address this uncertainty in several ways: Alternate Possible Futures Our homegrown forecasts are produced using many different data sources, including numerical weather prediction models, satellite data, ground station observations, and radar data. Most of the time, our forecast will be a reliable source of information (it’s better than the one we had at Dark Sky). But, crucially, we supplement the main forecast with a spread of alternate predictions. These are additional forecast lines that capture a range of alternate possible outcomes: A forecast showing multiple possible outcomes This accomplishes a couple things: First, the spread of the lines offers a sort of intuition as to how reliable the forecast is. Take the two forecasts below. In the first, the alternate predictions are tightly focused and the forecast can be considered robust and reliable. In the second, there is a significant spread, which is an indication that something is up and the forecast may be subject to change. It’s a call to action to check other conditions or maps, or come back to the app more frequently: A more reliable forecast A less reliable forecast Over time, you build up an intuitive sense of just how much you can actually trust the forecast. After using this for the past six mo

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