Midwest Overview - April, 2005

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April Starts Like Spring, Ends Like Winter

Warm and dry weather dominated the first three weeks of April, allowing signifcant spring planting progress in the central and southern Midwest.  However, a major change in the jet stream pattern over the U.S. during the fourth week of the month brought record snow and cold to the region.  A number of locations that were on pace for a top five finish for a warm April were knocked out of record contention because of the much colder weather.

The jet stream pattern was condusive to warm weather early in the month as a broad trough of low pressure  in the western United States produced a southwesterly flow of air through the Midwest (Figure 1).  Temperatures for the first 22 days of April ranged from 3F above normal in eastern Ohio and Kentucky to 12F above normal in western Minnesota (Figure 2).  By April 22 a change in the jet stream pattern was evident (Figure 3) with a strong low pressure trough developing of the central U.S.  The trough intensified and persisted through the end of the month, flipping the April temperatures from very warm to very cold.  During the period April 23-30 temperatures averaged 10F to 12F below average across most of Minnesota, Iowa, and Missouri, while at the eastern boundaries of the Midwest temperatures averaged "only" 7F to 9F below average (Figure 4).  When all was said and done temperatures for the month of April ranged from near normal at the far southern and portions of the Midwest to 5F above normal in portions of northern Minnesota and Wisconsin (Figure 5).

Precipitation was near to above normal in two sections of the Midwest this month (Figure 6).  The first was an area from central Minnesota south through the western three-quarters of Iowa.  The second area encompassed most of Kentucky, Iowa, and  east-central Indiana.   From southern Wisconsin through western lower Michigan, precipitation was less than 50 percent of normal.  The eastern half of lower Michgian would have been in the same situation but for the snowstorm that left more than 14 inches of snow on the ground on April 24.  Since the start of climatological spring (March 1) the central third of the Midwest from southwest Missouri northeastward through Michigan has recived less than 75 percent of normal precipitation (Figure 7).  The dry weather in April enabled agricultural producers to make significant progress in planting, but now moisture is needed to aid germination of the crops.