Occasionally you may see an image that is not updating correctly or shows old data.
There are several things that can cause this. The source (radar, satellite, etc.) may be down or having Internet problems.
Another likely cause is your browser is caching an older image and not updating to the most current image.
Sometimes pressing F5 (while you are on the page your having trouble with) will force the browser to get the current image.
Also setting your browser to always get the newest version of the page should help. Different browsers have different settings.
In IE8 you go to Tools / Internet Options / General Tab / Settings (Browsing history section) / and click "Every time I visit the webpage".
Click OK (twice) go close.