A post on the Google Blog informs us that Google now has a shortcut that provides a four-day weather forecast in a OneBox at the top of web search results page.
To use this new service simply begin your query with the word "weather" and then provide a location (U.S. only) or Zip Code. For example:
Weather Chicago Illinois
Google's weather shortcut is also available via Google SMS.
Btw, the weather shortcuts from Ask.com and Yahoo also provide info for major cities located outside of the U.S. A local weather shortcut is also available on some Local Yahoo!s. Examples:
Yahoo! Austalia/New Zealand
Ask Jeeves properties in the UK and Japan also offer Smart Search options including one for weather info.
+ Weather in Leeds
+ Japan Weather
4Info.net, an SMS-based info service, and Yahoo Mobile offer weather and other info for mobile web users.