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December 2000 Storm: Dewpoint - Another indicator of a front, the sharp contrast between dry and moist air, is apparent in this animation of dewpoint temperature (colors) and sea level pressure isobars (black lines). The strong gradient of the dewpoint (orange-blue contrast) is found at the leading edge of the polar continental airmass moving southeastward from western Canada into the central United States. The core of this airmass is marked by the high pressure center. The strong dewpoint gradient at the edge of the airmass identifies the cold front associated with the cyclone that moves northeastward as the cold airmass advances eastward behind it. Notice also how the Rocky Mountains are a preferred location for the boundary between dry and moist air.
This animation shows the sea level pressure isobars (black lines) and surface air temperatures (colors) as a continental polar airmass moved southward and eastward from Canada into the central United States. The leading edge of this airmass was a cold front (sharp blue/green boundary in the animation) that trailed southwestward from a strong low-pressure center. The low center was moving northeastward from the Mississippi Valley to New England. The cold airmass moved southeastward behind the cold front, eventually overspreading all but the southern and western fringes of the United States. Notice how the temperatures in the core of the airmass moderate as the cold high pressure center moved across the United States.
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