on Thursday, September 26, 2019
By Michigan Farm News
A major change in the upper air pattern across North America led to the development of broad upper air ridging across the Great Lakes region during the second week of September and a return to above normal temperatures and more frequent precipitation.
A slowly-wavering frontal boundary across Michigan during the 10th and 12th of the month brought an outbreak of severe weather and .50 to 1.5 inches of rainfall totals, the most widespread across the state since mid-summer. The warmer and wetter weather led to an acceleration of growth and development of most annual crops, both because of the warmer temperatures and to a reduction in moisture stress.
Mean temperatures for the 30-day mid-August through mid-September reporting period were heavily influenced by the northwesterly upper air pattern across the Great Lakes region during late August and the beginning of September, with averages generally ranging from 1 to 2 degrees Fahrenheit above normal across southeastern sections of the state to more than 4 degrees Fahrenheit below normal across the western Upper Peninsula.
As of mid-September, seasonal base 50-degree-Fahrenheit growing degree day totals relative to normal (since May 1) ranged from near or slightly above normal across far southern sections of the Lower Peninsula to more than 200 units below normal across most northern sections.
Just as importantly, there have been no reports of any first frost or freezing temperatures across the state (or region) so far this fall. Thirty-day precipitation totals ranged from less than 2 inches across portions of central and northern Lower Michigan to more than 5 inches across the central and eastern Upper and western Lower Peninsulas.
The most recent National Drought Mitigation Center Drought Monitor categorized just over 60% of the state in “D0” (abnormally dry) or “D1” (moderate drought) conditions as of Sept. 10, which is down slightly from the beginning of September.
As noted earlier, the recent jet stream change has resulted in above normal mean temperatures, with daily accumulations of 15-20 base 50-degree-Fahrenheit growing degree day units observed in most sections of the state during the past 1-2 weeks.
Latest medium-range forecast guidance calls for a gradual shift of the jet stream southward toward the Great Lakes once again by the end of the month, which would lead to somewhat cooler temperatures and more frequent chances for rainfall.
As a result, some forecast guidance does call for mean temperatures to fall back below normal levels at least temporarily during early October. Beyond that, however, the NOAA Climate Prediction Center outlook for September through November through the early winter season calls for above-normal mean temperatures state- and region-wide.
Normal- to above-normal precipitation totals are forecast. Overall, the pattern is still overall somewhat encouraging for moving crops forward towards physiological maturity.