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Chinook Melt
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The Chinook Indians were devastated by diseases brought by white settlers in the late 1800s, but the winds named for these Native Americans are still blowing strong in the western Rockies. Hi. I'm Dave Thurlow for the Mount Washington Observatory and this is The Weather Notebook.

The Chinook Wind is not called "snow eater" for nothing! This western wind can vaporize a few inches of snow in two hours, skipping the better known phase of melting known as slush. How does this happen?

Chinook winds blow in from the Pacific in late winter and early spring. Their moisture evaporates as they pass over the Rocky Mountains. Once the winds come down from the mountains onto the high plains, the air can be quite mild and extremely dry,. When a Chinook takes effect local temperatures can warm up from as low as 5 degrees below zero to 60 or 70 degrees Fahrenheit. The air is so dry that when it hits snow, it sucks up the moisture, changing the snow directly into water vapor, bypassing the liquid phasethat slushy phase-- entirely. Called sublimation, this is a common way for snow to disappear quickly in arid climates.

Not so in the East where the air typically stays more humid and the process of melting a whole snowpack is slower. Occasionally, though, a rapid thaw can occur, resulting in spring "freshets", with lots of run-off and even severe flooding. In January of 1996, Pennsylvania suffered severe flooding when over two feet of snow melted in two days. In that case, a little Chinook sublimation could have prevented a lot of liquid inundation.

Thanks today to writer Duncan McKee. The Weather Notebook is made possible by a grant from the National Science Foundation and the underwriter, Subaru, the beauty of all-wheel-drive.