Dan Mossop

The perfect way to show current conditions and a 3-day forcast in your sidebar, for a location of your choice. Great for travel sites, town or city sites, etc. It looks good, takes up little space and is easy to set up.
The widget uses accurate weather data from World Weather Online.
<h4>About the Weather Widget</h4>
The Weather Widget by Calcatraz is a compact WordPress weather widget for your sidebar. It has a neat, neutral design which fits in with almost any site. For the location of your choice (city, town, coordinates, ip address, etc) it shows the current weather conditions on the left and a 3-day forcast on the right.
The widget can display temperatures in both celcius and fahrenheit scales. It can detects the user’s language and shows the appropriate scale, or use a predefined scale. It also allows the user to switch scales, and remembers their preference.
There are now two styles: the default wide style (260 x 58px), and the new square style (133 x 116px) suitable for narrower sidebars.

Weather Widget by Calcatraz

A simple, compact weather widget which displays current conditions and 3-day forecast for the selected location.

Theme Egg

This is Weather Forecast widget plugin, You can add widget by installing this plugin. 
After Installing this plugin go to Appearence>>Widget and add widget to your sidebar.

Weather Forecast

This is Weather Forecast widget plugin, You can add widget by installing this plugin.

Weather Widget by Calcatraz vs Weather Forecast