The Midwest will experience changing weather conditions over the long holiday period. The most noticeable change will be the much more pleasant airmass that will move over the area for Labor Day. The current heat and humidity will be replaced by much cooler and drier Canadian air.The core of the heat will shift west, allowing Canadian air to slide down over the eastern part of the nation.
The changes will be the result of two fronts that move through the Midwest. The first is a front that stretches from central Michigan to extreme northern Kansas midday Friday. This front will produce scattered showers and storms as it heads south. A second more powerful front will sweep over the Midwest Sunday night again with scattered storms. It is behind this second front that the cooler Canadian air resides.
For the Chicago metro area, another hot and sticky day ahead of the first front. The front will move through the metro area this evening. Scattered storms are expected to form along the front late this afternoon into the evening. The area is outlined for possible severe storms. Saturday will still see highs in the 80s away from the lake, but a little less humid. Sunday afternoon will again see the chance of storms with the second front. It is Monday that highs will be only in the 70s with much lower humidity.
The metro area, and the Midwest need the rain. The graphic from the US Drought Monitor shows roughly the western 1/2 of the Midwest is at least "abnormally dry." As can be seen, parts of Iowa into northern Missouri are now in a "severe" drought category. Jim Angel, the Illinois Climatologist, has an interesting article describing the "flash drought" conditions that have developed. Drought is normally a long term process that takes many months to form, these conditions have formed rather rapidly.
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