The map for March 10, 2011, showed a large low pressure area over the Great Lakes region, with a strong high pressure area over the Canadian Maritime provinces. Though isobars, highs, and lows do provide part of the solution, it's also important for forecasters to look at the map in terms of the air masses that are involved. The warm tropical air mass is located over Cuba, the Bahamas, and part of Florida, signified by temperatures near 70°F and partly cloudy skies. A cold, dry air mass covers much of central Canada and the central United States with gusty northwest winds. There is also a cold air mass that covers New England and Quebec, with easterly winds that indicate a much different origin. Where do they meet? This is the question that answers with certainty where the fronts are.
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