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Name: Kristina
Status: student
Grade: 9-12
Location: VA
Country: USA
Date: Spring 2012


Question:
http://weather.unisys.com/nam/nam.php?plot=700&inv=0&t=4p

At the above weather link: The 700 mb Vertical Velocity plot is confusing in that the plot key uses the same colors for different values. For example: the key at the bottom uses the color yellow to denote -18, 6, and 30. How do I know what value yellow is on the plot?The same goes for the other colors.


Replies:
Kristina,

In areas where there is clockwise flow (high pressure) the vertical velocities should be negative and where the flow is counterclockwise (low pressure) the vertical velocities should be positive. That's the easy part. Why the color scheme is repeated for positive vertical velocities in the 12 hour forecast plot is a bit hard to fathom (note that this does not happen in the 24, 36, and 48 hour forecast plots). Note also that the forecast vertical velocities decrease with time, which may be why the repeating of the colors in the positive is only needed for the 12 hour plot.

I suspect that the upper color band in the 12 hour plot is not really used, unless there is one false very high forecast value that is causing the scale to be artificially increased.

David R. Cook Meteorologist Climate Research Section Environmental Science Division Argonne National Laboratory


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