by Jeff Andresen

An unusually active jet stream pattern continued across the Upper Midwest during the first half of August, with the passage of major troughing features and widespread rainfall Aug. 6-7, Aug. 11-12 and again Aug. 14-15. 

Rainfall totals for the mid-July through mid-August reporting period ranged from just under 2 inches across portions of eastern Upper and extreme northern Lower Michigan to more than 6 inches — more than 200% of normal in some locations — across much of the southern half of the state.

Across much of central and southern Lower Michigan, heavy rainfall provided ample moisture for most crops moving through water-sensitive growth stages. It also led to problems with localized standing water, delaying wheat and forage harvests and a flush of weed growth.

In contrast, in some western sections of the state where rainfall was much less, abnormal dryness and moisture shortages and crop water stress problems continued. As of mid-August, the U.S. Drought Monitor categorized 60% of the state’s area in abnormally dry or drought categories.

This includes some central and southern areas of the state that have recorded recent heavy rainfall but have not yet fully recovered from long-term water deficits. Driest conditions (D2 severe drought) are located in portions of the west central Lower and far western Upper Peninsulas. 

Mean temperatures for the past 30 days ranged from near normal across southern sections of the state to 2 to 4 degrees F below normal across northern sections. The cooler weather helped reduce moisture stress issues in dry areas of the state but slowed crop growth and phenological development of crops.

Harvest weather outlook

After a very active late July and first half of August, the latest medium-range forecast guidance calls for a major change in the jet stream pattern across the Upper Midwest with the approach of a broad upper air ridge from the west expected to bring relatively warmer and drier weather to Michigan.

This is somewhat consistent with the new ensemble of NOAA Climate Prediction Center Long lead outlooks for the upcoming fall season. The longer lead forecasts are based more heavily on El Nino conditions currently in place across the eastern equatorial Pacific region and differ somewhat from previous editions.

For the month of September, the official outlook for Michigan calls for equal odds of below-, near-, and above-normal mean temperatures and for normal- to below-normal precipitation totals (previous outlooks had also called for the equal odds scenario for precipitation).

For the September through November fall season, the outlook calls for near- to above-normal mean temperatures and for normal- to below-normal precipitation totals.

Collectively, while these outlooks may suggest some continuing issues with late-growing-season water shortages in some parts of the state, they would also offer some real benefits for areas recovering from recent heavy rains, for later-maturing crops, and for fall harvest and other fieldwork activities.

Andresen writes for MSU Extension and is the state climatologist for Michigan.

Source: MSU Extension