Usage:
  weighted_average_raws.php?area=name&ids=id_list&cats=cat_list&weights=weight_list&day=DD&month=MM&year=YYYY
    where:   
                area = name asigned to group of RAWS stations
             id_list = a comma-separated list of RAWS stations by WIMS id 
            cat_list = a comma-separated list of WIMS climate/fuel identifiers corresponding to the id_list stations
         weight_list = a comma-separated list of weights to apply to the stations in the id_list 

    the following are optional parameters can be omited if you only want the latest data:
                  DD = day to retreive
                  MM = month to retreive
                yyyy = year to retreive