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July-August 2010

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Forecast Center

When a powerful weather system brings warm, moist low-level air and cold upper-level air together, the stage is set for some of the most violent weather on the planet. This configuration was recognized over 120 years ago when expert John P. Finley conducted the first detailed tornado study for the U.S. Army Signal Service, a predecessor to today's National Weather Service. In this issue's puzzle we'll take a special look at one of the most potent weather systems to ever strike the United States.

This weather map depicts a midday weather situation in April. 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.

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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