...WINTER WEATHER ADVISORY FOR THE BIG ISLAND SUMMITS... An upper level trough passing over the Big Island through tonight will produce snow showers through this evening...icing on roadways and low visibility due to freezing fog could persist through the night. * WHAT...Snow up to 2 inches and freezing fog expected. * WHERE...Big Island Summits. * WHEN...Until 6 AM HST Saturday. * IMPACTS...Travel could be very difficult due to icing on roadways and freezing fog. Blowing snow will significantly reduce visibility at times, with periods of zero visibility.