Jeff Andresen | May 23, 2018
A nearly stationary frontal boundary across the Ohio Valley led to almost daily rounds of showers and thunderstorms across portions of Michigan during the second week of May, resulting in heavy rain, localized flooding and, in some areas, a prolonged stoppage of spring fieldwork activities.
Conditions were most challenging across southern Lower Michigan, where more than 6 inches of rain fell during the first half of the month. In contrast, rainfall totals for the same period were much less across northern sections of the state, allowing continued progress of spring planting.
Mean temperatures for mid-April through mid-May ranged from near normal across southern sections of the state to 3 degrees F below normal across the north. The means statistically smooth out much below normal temperatures during most of the latter half of April with above normal temperatures during the first half of May. This trend is also reflected in seasonal growing degree day accumulations.
Precipitation totals for the reporting period ranged from less than 2 inches across central and western sections of the Upper Peninsula to more than 6 inches across the southern 2-3 tiers of counties in Lower Michigan. Normal total precipitation during the reporting period ranges from about 2.25 inches across some northern sections of the state to just over 3 inches across central and southern Lower Michigan.
Medium range forecast guidance has been consistent recently in suggesting an upper air ridging feature across the central U.S., which would lead to warmer than normal mean temperatures during much of the remainder of May and possibly longer. That guidance has also shifted somewhat in calling for less overall precipitation than had been the case in recent weeks, with normal- to below-normal precipitation totals now expected in Michigan for the same timeframe.
Collectively, the medium range outlooks suggest improving conditions for spring fieldwork and planting, especially across southern sections of the state hit by recent heavy rains. However, in some northern sections of the state missed by recent rainfall, it may lead to some topsoil moisture shortages.
In the longer term, there have been some changes in the latest NOAA Climate Prediction Center long lead outlooks, which earlier had called for warmer and wetter than normal weather for much of the first half of the growing season. The new outlook for June now calls for the near equal odds scenario of below-, near-, and above-normal values for precipitation totals and mean temperatures. The June–August summer outlook is closer to previous forecasts and calls for near- to above-normal mean temperatures and precipitation totals.
Andresen is a professor of Meteorology/Climatology with Michigan State University’s Dept. of Geography, Environment, and Spatial Sciences; MSU Extension specialist and the state climatologist for Michigan.