A strengthening upper-air ridge across the Midwest brought warm, dry weather to most of Michigan during the middle of September, allowing maturing crops and soils to dry/drain following a period of much- above normal rainfall during late August and September.
Mean temperatures during the mid-August through mid-September reporting period were above-normal statewide, ranging from about 2 degree F across western sections of the state to more than 4 degrees F across central and eastern sections.
Rainfall totals for the period ranged from more than 10 inches in portions of west central Lower Michigan to less than 2 inches across the southeastern Lower Peninsula. The late August/early September rainfall dramatically reduced drought conditions in many parts of the state, with only 28 percent by area remaining in D0 (Abnormally Dry) or higher categories by the second week of the month (vs. more than 70 percent near its peak at the end of July and beginning of August).
However, even with the recent rain- fall, moderate drought was still reported across northeastern and southeastern portions of Lower Michigan and across the far eastern Upper Peninsula as of the middle of September.
Given the abnormally warm growing season, most crops are phenologically advanced one week or more versus normal. While many crops have been able to benefit from the late-season rainfall, the combination of persistent rain and high humidity have resulted in late season disease pressure for some crops.
The recent spell of warm, dry weather has been nearly ideal for the maturation of most annual crops. However, latest medium range guidance suggests a more active weather pattern across the Great Lakes region for late September and early October, with the passage of a series of low-pressure centers and associated frontal boundaries resulting in normal to above- normal precipitation totals.
Mean temperatures during the same timeframe are projected to remain at normal to above-normal levels. The guidance also hints at the potential for a period of upper air troughing and the transport of at least one Canadian origin air mass into the Upper Midwest at some point near the end of September or early October.
At this time of the year, these upper-air patterns are frequently associated with early fall frost/freeze events. And while the medium-range forecast guidance has relatively low accuracy/skill so far ahead, it is worth remembering that we are definitely within or approaching the normal date range for the first 32-degree or lower temperatures of the fall season (so far this season, sub-freezing temperatures have only been reported at a few spots in Upper Michigan).
Climatologically, this event on average ranges from the beginning of September in interior Upper Michigan to early October across much of central Lower Michigan to late October across the southwestern and southeastern corners of the state. Regard- less, almost all long-lead outlooks for the remainder of the fall season continue to suggest warmer-than-normal mean temperatures during the next several weeks, which would favor most fall harvest and planting operations.
Andresen is a professor of Meteorology/Climatology with Michigan State University’s Dept. of Geography, Environment, and Spatial Sciences; MSUE specialist and the state climatologist for Michigan.