The storm system that was organizing yesterday over the Plains has moved into the Midwest on it's way to the mid Atlantic coastal region where snow of 12+ inches will fall inland. Yesterday morning there was surface low pressure over North Dakota with a strong upper level disturbance and another low over Oklahoma with a southern branch of the jet stream. This Tuesday morning the lows have combined over western Kentucky with the upper level system deepening over Iowa.
The graphic shows the mid morning water vapor satellite picture. The picture is showing the moisture from roughly 10,000-30,000 feet. The brighter white and purples show higher clouds which are thick and very cold. The red and orange over Texas shows very dry air moving east along the southern jet stream. The swirl over western Iowa is the upper level low dropping southeast. The deep moisture (white/purple color clouds) is ahead of the low. This deepening upper level low is the energy that is driving the entire storm system.
For the Chicago metro area, there is some good news for those that do not like snow, or are impatiently waiting for spring weather. The system is shifting a little south and a little weaker than it looked yesterday. The result will be a little less snow over the area. Snowfall over the metro area will range from around 5 inches far northeast near the Wisconsin border to local 10 inch amounts for the southern sections. General snowfall central sections very roughly along the I88 corridor including the city will run 6-8 inches. Overall snow will be about two inches less than originally expected yesterday. This will be the largest snowfall for central and south sections of the metro area this winter.
Once the storm moves out tonight, spring weather will finally start to show up. We are now in meteorological spring. The normal high now for Chicago is up to 42 and rising. Highs will be in the low to mid 30s Wednesday and Thursday, held down by the new snowpack. By Friday highs reach to near 40, and into the 40s through the weekend into early next week. The warming a product of a developing upper level system over the Plains which will switch the upper level winds to the southwest. As is typical in March, any snow will do a fairly quick melt.
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