During the past few issues, we've talked about summer heat in Arizona and tropical Caribbean showers, but the calendar shows us that winter is fast approaching, and it's time to get back in the saddle with cold season forecasting. This means getting familiar with frontal systems, the development of polar air masses, and the meaning of terms like “baroclinic.” There's no better place to start than with Alaska and northern Canada, where the meteorological summer has ended and the Arctic is beginning to flex its muscles.
This weather map depicts conditions in September during the evening hours. 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.