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Vintage
Tue May 18, 2004
Listen in RealAudio 
Hi, I'm Bryan Yeaton for The Weather Notebook. Breathe deep that mountain air. A
crisp, white Canadian Arctic air with a subtle hint of snow. Vintage, perhaps a few
weeks ago. Still clean and refreshing.
Describing air like a glass of wine is not all that farfetched: early weather observers
relied on their senses to distinguish between different air masses, and made
forecasts accordingly.
Air masses gather unique and uniform characteristics of temperature and moisture
from their birthplace. Air masses born over tropical oceans become warm and moist;
those formed over polar seas, cold and damp. Air masses spawned in polar
continental areas are, naturally, cold and dry; and hot, dry air masses arise in desert
and arid regions.
Air mass breeding grounds ring the globe, tucked away from strong wind belts so that
the fledgling masses can mature. Eventually, all air masses are pushed from their
nest by global wind currents forcing them to mingle with other air masses. At any given
moment, about 50 distinct air masses travel the globe.
Cold air masses seek warmer latitudes while warm ones prefer northward treks. The
travelers are altered by their journeys. Many clash vigorously with opposing systems,
producing severe thunderstorms or blizzards along their boundaries or fronts. At times,
large spiral, cyclonic weather systems, spin off along the front.
Old air masses, travel-worn and battle-scarred with little similarity to their youth, settle
into some quiet corner of the globe. There, they undergo a transformation, slowly
assuming the properties of their hideaway. If they remain long enough, they are totally
transformed, and ready to begin new journeys.
Thanks to our contributing writer, meteorologist Keith Heidorn. The Weather Notebook
is produced by the Mount Washington Observatory, a vintage location. We are funded
by the National Science Foundation and Subaru -- Driven By What's Inside.
Today's Links
Air Masses: A Base for Weather Analysis
http://www.islandnet.com/~see/weather/elements/airmasses.htm
The Online Meteorology Guide: Air Masses
http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/af/arms/home.rxml
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