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March-April 2011

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Forecast Center

The winter season brings a dramatic pattern shift to the United States. With temperature contrasts between land and sea increasing sharply, weather systems strengthen. This means that not only can there be incursions of tropical air northward, but with the cold season taking hold there can also be massive outbreaks of arctic air southward from the polar regions. This puzzle takes a look at one such event in 2011.

This weather map depicts a midday situation in January. Draw isobars every four millibars (996, 1000, 1004 mb, etc.) using the plot model example at the lower right as a guide. As the plot model indicates, the actual millibar value for plotted pressure (xxx) is 10xx.x mb when the number shown is below 500, and 9xx.x when it is more than 500. For instance, 027 represents 1002.7 mb, and 892 represents 989.2 mb. Therefore, when one station reports 074 and a nearby one shows 086, the 1008-mb isobar will be found halfway between the stations. Then try to find the locations of fronts, highs, and lows.

For further information, along with helpful hints and advice, visit

TIM VASQUEZ is a former Air Force forecaster and author of Digital Atmosphere, a weather forecasting software program. He lives near Norman, Oklahoma, where he keeps busy as a weather consultant and software developer.

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