I need to make a cake for a Halloween event at my daughters school. The cake will be in the hot California sun all day. What kind of frosting and decorating can I do that will be safe to eat and not melt after so much time in the sun?
Thanks
Kate

Please see this video by Bronwen Weber. She shows what happens to a tiered cake that has been decorated in buttercream after a little while at 110º.

Rather than attempt to do a cake that will withstand the sun, I would suggest that you/the school find a way to provide some shade for your cake, or, have them bring it from a cooler indoor spot to outside for the display at the last minute.

OMG!! I just watched that video. This should be required viewing for anyone planning an out door event in the summer.

I have made 100s of b'cream cake in central CA and not had the problem that video shows! Yes, it does matter exactly which recipe and how hot it gets but as my pix show many a cake has survived outdoors.
I highly recommend this recipe:
http://cakecentral.com/recipe/2-icing

I once set up a wedding cake (at the bride's insistence) something like 10 am in the bride's front yard - not a tree/shrub or other shade around. I learned much later that the reception didn't happen until around 4 pm. I was told by someone who attended that the cake was a 'bit dry' but didn't melt or have any other problems.
Quote from dayti:....... suggest that you/the school find a way to provide some shade for your cake, or, have them bring it from a cooler indoor spot to outside for the display at the last minute......

Totally agree w/this advice