function toggle_extended_forcast() {
   for (var i = 3; i < 10; i++) {
      thisTr = document.getElementById('wx' + i);

      if (thisTr) {
         if (thisTr.className == "hiddenRow") {
            thisTr.className = "nonHiddenRow";
         }
         else {
            thisTr.className = "hiddenRow";
         }
      }
   }
}