It appears as if the Google Personalized Home Page now allows you to add "themes." If you visit that page, on the top right you may notice a link named "Select theme."
If you click on the "select theme" link, up comes a box of several themes you can choose. The list includes; Classic, Beach, Bus Stop, City Scape, Sweet Dreams, Tea House and Seasonal Scape.
I selected Bus Stop, which looks like this:
Google then asks you to enter in your zip code so that the theme you selected with dynamically change based on your currently weather. I suspect that if its snowing, there may be snow around the theme, and so on.
The box says:
This theme will dynamically change to match your local weather conditions.
Please enter a location (your city and state or zipcode) to update this theme correctly.
Forum discussion at DigitalPoint Forums.