Jeff Andresen, Agricultural Meteorology and Geography

On Monday, September 21, showers and thunderstorms associated with the weather disturbance that brought extended heavy rain and flooding to much of the south and Ohio Valley during the past week ended an extended period of mostly sunny, dry weather across Michigan. Many areas had been dry since August 30. Forecast guidance is now suggesting some major upper air changes during the upcoming week leading to a cooler, more unsettled weather pattern.

In the short term, an upper “cut-off” low spinning counterclockwise across the central Great Plains is forecast to slowly move towards and through the Great Lakes region by the end of the weekend. While this feature remains to our west, southerly flow, abnormally warm temperatures, and high humidity will persist with the chance for showers and thunderstorms continuing through Wednesday evening, September 23. Best chances for rainfall will be across southern sections of the state during the afternoon and early evening hours. Rainfall totals are forecast to generally remain in the 0.1-0.25 inch category where rain falls. High pressure will move into the region late Wednesday and bring fair and cooler weather to the state Thursday and Friday. The cut-off low is forecast to move through the region this weekend with a good chance for more rainfall Saturday and Sunday. High temperatures the next few days will gradually fall back from the low or mid-70's north to the low 80's south on Wednesday to the mid-60's north to mid-70's south by Friday. Lows temperatures will generally range from the upper 40's north to the upper 50's south.

Further ahead, the forecast guidance has been very inconsistent with its projected solutions for the early to middle part of next week. Most recent guidance suggests a period of northwesterly flow aloft and much cooler than normal temperatures and at least the potential for a killing frost/freeze event across much of the state. Given the inconsistency of the models lately, I am not sold on this idea just yet. Medium range forecast guidance is also having problems converging on a projected upper air pattern. As it stands right now, the NOAA Climate Prediction Center 6-10 day and 8-14 day outlooks for September 27- October 1 and September 29- October 5, call for mean temperatures to range from below normal levels across southern sections of the state to near normal in the north. For precipitation totals, the outlooks call for a range from below normal totals across western and central Upper Michigan to near normal elsewhere across the state during the 6-10 day time frame. During the 8-14 day period, below normal precipitation totals are forecast statewide. It is important to note that forecaster confidence in these outlooks is considered below normal due to the recent inconsistencies in the model guidance.