Midwest Overview - April 2007
Cold Weather Dominates April
Average daily temperatures were below normal across most of the Midwest this month, with the exception of north-central Wisconsin where temperatures were near average (Figure 1). The largest departures from normal (-4°F) occurred on the western and southern periphery of the region. Average daily maximum temperatures ranged from 2°F to almost 5°F below normal (Figure 2), while minimum temperatures ranged from about 3°F below normal in the southwestern half of the region to near normal across the northeastern half.
Precipitation was highly variable across the region this month both in time and space (Figure 3). Precipitation was one and a half to two times normal across much of northwestern Minnesota, and across Iowa into northwestern Illinois. The driest area was north-central Wisconsin, which received less than 75 percent of the normal monthly precipitation.
Most of the precipitation in northwestern Minnesota came during the first and third weeks of April. During the first week of the month the precipitation fell as snow as a late winter/early spring storm produced blizzard conditions over the upper Midwest April 4-6. Another low pressure system over the Midwest on April 22 spawned numerous showers and thunderstorms across northwestern Minnesota, resulting in two to three time the normal weekly precipitation. The precipitation during the first three weeks of April across the upper Midwest did bring some improvement in the drought conditions that have been ongoing since July 2006. However, the return of dry weather the last week of April in Minnesota and the northern half of Wisconsin ended any relief for the time being. Moderate Drought was developing back into northwestern Wisconsin at the end of the month.
Heavy snow fell during the month in northern Minnesota and in the lake-effect snow belts in Michigan and Ohio (Figure 4). The storm of April 3-5 deposited more than 3 feet of snow on the Michigan Upper Peninsula, and strong winds whipped the snow into drifts as high as 8 feet.
Early April Freeze Causes Significant Crop Damage
Fruit trees began to bud and the landscape quickly greened up in the much warmer than normal temperatures the last ten days of March and the first few days of April. Unfortunately, following the major winter storm the first week of April cold air plunged south through the Midwest and remained entrenched over the region for the next five days. Temperatures averaged 12°F to 20°F below normal from April 6-9 (Figure 5), and there were numerous minimum and low maximum temperatures set across the Midwest. A hard freeze (temperatures less than 24°F) occurred over the entire region on April 7, with subfreezing temperatures well south of the Ohio River. Subzero readings occurred in Minnesota, with a low of -8°F Embarrass, MN on April 8. The freezing weather damaged peaches, apples, and grapes in southern portions of Illinois and Indiana, and strawberries in Kentucky. Winter wheat in the Midwest was also damaged. The most damage appeared to be in Kentucky where the winter wheat crop went from only 5 percent in poor to very poor condition on April 1 to 80 percent in poor to very poor condition on April 22.
Spring Flooding Persists
Spring flooding occurred at various places in the Midwest throughout the month. In early April, flooding in Minnesota and Wisconsin was due to ice jams on rivers and runoff from melting snow. Later in the month, river and stream flooding in Iowa, Illinois, Indiana, and Michigan was due to the runoff from heavy rain. At the end of the month, rivers in central and eastern Iowa were still in flood but were receding after the three to four inches of rain on April 24-25. The Illinois River from south of Henry to Beardstown, IL was in minor to moderate flood, and minor flooding was occurring at several points along the Wabash River in Illinois and Indiana.