In this issue we'll look at an extratropi-cal low with a cold front, a warm front, and an occluded front moving across the Midwest. This type of system is actually quite common, affecting the nation multiple times during the cool season. However, on this particular day, it proved to be a prolific snow producer. It brought more than a foot of snow to parts of Wisconsin, Michigan, and Ontario and resulted in hundreds of flight cancellations in Chicago, Detroit, and Milwaukee. This weather map is for an event during the early evening hours in February. Draw isobars every 4 millibars (1008,1004,1000, 996, 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 millibars when the number shown is below 500 and 9xx.x millibars when it is more than 500. For example, 027 represents 1002.7 millibars and 892 represents 989.2 millibars. Therefore, when one station reports 074 and a nearby one shows 086, the 1008-millibar isobar will be found halfway between the stations.
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