In April, Ben Brooks wrote two detailed roundups of the market for weather apps on the iPhone. (First, second.) His conclusion was that the market is saturated with junky apps that try to do too many things, and so it’s hard to find something reliable, fast, and simple. (I don’t think anyone’s crazy about the preinstalled Weather app on the iPhone.)
Sometimes, though, you don’t need an app to find what you need. If you google “weather” on your Android or iOS device, you get a nice little treat:

That’s current conditions, with a slider that gives you the forecast for the rest of the day, plus a quick look at the next four days. Depending on your phone’s settings, you might need to turn on location services.
Obviously it has limits. It’s not a terribly detailed forecast. If you’re trying to track the emergence of localized storms—completely hypothetically, if you’re trying to figure out whether to cancel a soccer practice—then you’ll need something with radar. In that case, you can just tap one of the links offered right under the weather forecast.
Interestingly, Google’s mobile weather service appears to draw on a slightly different data source than it’s conventional one. Here’re two screenshots of the weather in New Britain, CT, taken at the exact same time. First, from my MacBook:

And here are the results on my phone:

People aren’t likely to change their plans based on a 3 degree difference, but it is interesting that they serve different results. Also, notice that this time there’s no button for location services, because I googled a specific place (i.e., New Britain, CT weather), and so Google inferred that I didn’t need further location choices.
Google’s service started in January, so obviously this isn’t breaking news, but it might well be handy as you try to plan impromptu summer activities! (Rumor has it you can also check the weather by “going outside”—but I can’t confirm that.)
Photo by Flickr user snappybex / Creative Commons licensed