Weather Underground's conditions and forecast data comes fast, simple, and without a lot of gimmick-y offers. A Chrome extension built around the service offers WUnderground's data in a toolbar button icon, mouse-over details, and a mini-page when clicked.
Compared to a fair number of other weather alert apps and browser extensions, Weather Underground for Chrome—which appears unofficially, if lovingly, coded—feels the least annoying and the most helpful. The temperature in degrees and a basic conditions icon is always a glance away, while a more detailed explainer ("39.8, light drizzle mist, in Buffalo, NY") can be had by simply stopping your mouse cursor on the button. Click it, though, and you get just enough data on what's happening in the world outside your window, along with a four-day forecast and links to more detailed stats.