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Migration of Spring
Fri Jun 13, 2003
Listen in RealAudio 
Hi, I'm Bryan Yeaton for the Weather Notebook. With today's increasing demands for precision,
we expect the seasons too should begin on the dot. Last winter, the media decried a severe
early cold snap for coming two weeks before "official" winter, as if its start, like the
seasons of Camelot, was ordered by decree.
Seasonal rhythms, however, do not follow precise clocks. Spring illustrates this perfectly
because it has such dramatic visible indicators. New life blossoms each Spring after Winter's
sleep.
Our best indicators for watching Spring's northward migration are not weather instruments, but
plants and animals. For centuries, farmers and naturalists watched nature closely, recording
in journals dates for various events particularly plant budding and flowering. Early American
climate studies were based on these records, called phenology.
For example, over decades the budding dates of red maples were recorded all through the
Eastern States. So too, the first songs of robins and spring peeper frogs. Knowing such dates
ultimately helped farmers plan crops. Today, we know many plant indicators begin with the
onset of regular 44F-plus temperatures. Robins return to sing at 35F, and spring peepers at
50F.
Phenological studies have established Spring moves northward at 17 miles per day at sea-level.
Thus, if red maples bud in Washington March 20th, they will bud in Baltimore two days later
and New York City two weeks hence.
Thanks to our contributing writer, meteorologist Keith Heidorn. The Weather Notebook is a
program of the Mount Washington Observatory, on the web at www.mountwashington.org. We are
funded by Subaru of America, and the National Science Foundation.
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