When I display the dashboard while I'm at work, the weather widget is often incorrect. My company's web proxy caches old values, causing me to see reports that are often several days out of date.
This is not surprising. Many web pages end up out of date due to this problem. Telling my web browser to reload the page (which produces a slightly different HTTP request, directing the proxy to not use a cached value, and to update its cache) results in my getting the current page.
The Weather widget, however, is not a web browser. Dashboard widgets have no menu bar, and this one has no buttons on the GUI. I did notice that the widget fetches its content whenever Dashboard activates, so I would hide and then show the Dashboard to make Weather try again. Usually, it would get a current report after a few repetitions.
Today, however, this didn't work. After several dozen repetitions, the widget was still showing yesterday's weather information. Out of frustration, I typed CMD-R (the usual "reload" key used by most Mac web browsers). Much to my surprise, the widget immediately reloaded (including a really nifty looking graphical flourish), and immediately switched to the current report.
Even more interesting is the fact that this works for all widgets. Click on any widget, and then type CMD-R, and watch it reload its content with the same graphical flourish. It doesn't change the Calendar widget, but it did cause my Ferengi Rules Of Acquisition widget to pick a new rule.