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Since You Asked: Medford Airport makes it snow

I've heard recently that the airport releases a product into the air to help "defog" the landing area at MFR. Is this true? How is it done and what exactly is the substance?

— Jenn H., Medford

You've asked us this question a bit early this year, Jenn — this may be your first time but we get it like clockwork every December, with good reason. We typically don't answer it until a couple of days before Christmas. Maybe the fog came early this year?

Not only have we answered it in this column, but we did a full story in the 2006 Our Valley edition. You can find the whole story there, including an interview with two of the pilots who have done it. See below for details.

Long story short, a little Cessna plane goes up in the wee hours of the morning when it is foggy and very cold. A grinder chews up dry ice (solid/frozen carbon dioxide) into little bits and drops it into the air. The fog (water droplets) condenses and freezes on the carbon dioxide pellets. If you're close to the airport you might see the "fog" on your car fallen as tiny rods of ice, like primitive snowflakes.

There are other methods to seed fog that use propane or silver iodide, but in Medford we use dry ice. It's important to note that it only works when it's very cold, but that's typically when we have fog in the Rogue Valley. Dry ice melts and evaporates quickly into the air, so there is no chemical hazard.

For more information, go to the Mail Tribune Web site and search for "cloud seeding."

To find a PDF of that Our Valley article, go to www.our-valley.com/2006 and scroll down to "Cloud seeding: Clear the runway," or use this abbreviated address — tinyurl.com/2vne8v — that will get you right to that article.