An early fall severe weather outbreak is expected over the western part of the Midwest today, Friday. Unseasonably warm and humid air with dew points around 70 is in place ahead of an advancing upper level trough coming out of the Rockies, in combination with deepening surface low pressure over Nebraska, and the main warm front from southern Nebraska to southern Wisconsin. The ingredients will combine today to produce severe storms with tornadoes, possibly strong, in the indicated areas in the graphic from SPC.
The upper level trough is going to be very slow moving. From a position over Colorado this Friday morning, the center is expected to have moved east only to western Iowa by Sunday morning, southern Illinois by Monday morning, and Michigan by Tuesday morning. Needless to say, the slow movement will produce numerous rounds of showers and storms ahead of the cold front associated with the low pressure, and then clouds and scattered showers with the upper level system itself into Tuesday. Locally heavy rains are expected in the warm air, with blizzard conditions to the northwest of the surface low. Moisture from tropical storm Karen will also move northward from the Gulf to interact with the upper level system. The severe storm threat will also gradually shift eastward over the weekend, but the highest threat is today.
For the Chicago metro area, a secondary warm front has stalled just south of the city. Highs today will range then from only the mid 70s in the clouds far north metro to the mid 80s with sunshine far south metro. Best chances of showers and storms are far north metro this afternoon and night, over the entire area Saturday afternoon and night, and then a chance of showers Sunday night into Monday with the upper level system. Highs will drop into the 65-70 range for Sunday, and then continuing through next week.
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