The second in a string of clipper systems moved over the Midwest last night. These systems are moving from northwest to southeast along a "baroclinic zone" (temperature gradient zone) that is sitting over the Midwest. Cold arctic air to the northeast of the zone and milder Pacific air to the southwest. The rather compact systems zip along the zone, like along a zip line in the atmosphere.
For the Chicago metro area, the system zipped through in the hurry. The system left from a dusting to about 1/2 inch of fluffy snow over the area. The system coming through late tonight and into Monday will be the strongest of the bunch. Rather well organized low pressure will move from eastern Montana this afternoon to southern Indiana Monday evening. The low will be able to pull a little more moisture over the area than the previous two. With the snow water ratio expected to be from 15 to 1 to 20 to 1 during the event, this will be the largest snow producer of the season. Some lake effect might even briefly enter the picture as winds briefly turn in off the lake during midday before becoming northwest late in the afternoon.
The combination of a little more moisture, good lift, high water ratio, and a little lake effect will all combine to produce the biggest snow event so far this winter. Of course that is not saying much considering how little snow we have seen this winter. The graphic, which shows the probabilility of at least one inch of snow, shows just how narrow this snow corridor will be, typical of a clipper system. The heaviest snow with a band of 3-5 inches will be from roughly Rockford north to just north of Chicago. Amounts will taper off to the southwest with far southwest sections of the metro area seeing less than 1 inch of snow for tomorrow.
The fourth and final clipper will move through the northern Midwest on Tuesday. Most of this snow will fall from extreme north Illinois northward. For the Chicago metro area just a few flurries south to a light accumulation north near the Wisconsin border for Tuesday. The main news will be the warmer temperatures that will start to move over the area beginning Wednesday. From highs only in the teens today we move into the 20s Monday and Tuesday with highs well into the 30s for Thursday and Friday and 40s hopefully for next weekend. These will be the days some of our snow will begin to melt.
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