Jeff Andresen, Agricultural Meteorology and Geography

After an extended period of mostly sunny, dry weather across the state and region, forecast guidance is now suggesting some major upper air changes during the upcoming week. The upper air ridging pattern across the region that has led to the abnormally dry conditions (in the State Climatology Office, we=ve referred to it as our Michigan version of “California weather”) will give way to a troughing pattern by early next week, resulting in cooler and wetter weather. In the shorter term, a weak cool front will move through the state Friday, September 18, possibly setting off a few widely scattered showers or sprinkles. Most areas will remain dry and experience only a temporary increase in cloudiness and a wind shift to the north by late in the day. High pressure behind the front will move into the state by Friday evening, bringing clearing cool, dry and fall-like conditions. Some scattered light frost will be possible overnight Friday into Saturday morning, mainly in interior sections of the Upper and northern Lower Peninsulas. The high pressure should lead to fair and dry conditions Saturday and Sunday. By Monday, the transition to the upper air pattern mentioned above should be underway with the threat of showers statewide.

An unsettled weather pattern is likely through the middle of next week with a chance for rainfall on a daily basis. High temperatures the next few days will generally range from the low or mid-50's far north to the mid- or upper 70's far south. Lows will range from the 40's north to 50's south except for Saturday morning, when 30's are likely across northern and central sections of the state. Medium range forecast guidance is primarily based on the upper air pattern change noted above (ridging across western North America, troughing across central and eastern sections), although latest versions suggest the strength of the troughing may be less than in previous model. This has very important implications for our forecast, as the new trough will bring the chance for frost and freezing temperatures to at least parts of the region during the middle to latter part of next week. (Earlier versions of this guidance more strongly suggested the likelihood of widespread frost across Michigan and the Great Lakes region.) The other hint from the latest guidance is that this upper air change may be somewhat temporary with the troughing feature moving out after a few days resulting in a gradual moderation of temperatures.

As it stands right now, the NOAA Climate Prediction Center 6-10 day and 8-14 day outlooks for September 22-26 and September 24-30, both call for below normal mean temperatures state- and region-wide. Based on the most recent forecast guidance, I am personally hoping for and expecting a bit more moderate conditions than this scenario. For precipitation totals, the outlooks call for above normal totals statewide during the 6-10 day time frame with near normal totals during the 8-14 day period.