Okay, it's really only one umbrella, but I think it might be worth it. After all, if you're caught unprepared, you'll be soakced for the duration of the day, and your nips will be showing, as in the photo above.
[$69.99, ThinkGeek]
This umbrella was selling for $139.95, over at Hammacher Schlemmer, but is now available at ThinkGeek for half the cost.
The Ambient Forecasting Umbrella was one of those obnoxiously large ones I love, with that dual-canopy design that is supposed to better withstand strong winds (it totally works; I have the same thing going with my Nike Golf umbrella).
What really sets it apart from other massive umbrellas, however, is the built-in radio receiver, that receives weather data for 150 U.S. locations from Accuweather.com. An LED located at the bottom of the umbrella's handle flashes in proportion to the likelihood of precipitation in your area; if there's a 100% chance, it will flash rapidly, while a 10% chance will cause it to flicker slowly.