As winter arrives, American forecasters once again shift their attention to the Pacific Ocean and Canada. Cold fronts are staples of cold season forecasting, and they're some of the easiest systems to analyze. In this issue, we'll not only locate the front, but we'll also explain in detail what drives it and take a look at it from a forecaster's perspective.
This weather map depicts conditions in November 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.