The new UV forecasting website - http://uvawareness.com/ - is a very useful tool. It provides a four day hourly UV forecast from 6 a.m. to 6 p.m. for just about any location world wide.
This UV forecast data is harnessed from NOAA UV Index forecasting which uses the TUV radiative transfer code for deriving the erythemally weighted downwelling UV fluxes. This NOAA UV Index is computed using forecasted ozone data, and cloud amounts. In addition, climatological aerosol loading, variable snow and constant bare earth albedo, and elevation are used in the model.