Midwest Overview - May, 2005

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May Dryness Turns to Drought in the Central Midwest

The month of May has been cool and dry in the Midwest. Precipitation totals of less than two inches predominated in most of Missouri, Illinois, northern Indiana, and southern Michigan (Figure 1). Since the normal May precipitation is more than twice this total in these states, a large swath with less than 50% of normal precipitation for the month was evident in the same region (Figure 2). Only western Iowa and Minnesota were above normal in precipitation this month. Illinois had its 6th driest May since 1895, and both Kentucky and Missouri had their 9th driest May. Because upper level troughs and Canadian high pressure systems were common, the air was also cooler than normal during May (Figure 3), with anomalies ranging from slightly below normal in the southwestern Midwest to 3-5°F below normal in parts of the northern Midwest. The cool conditions kept crop water demand low, which helped stretch the existing soil moisture. In addition, the period autumn 2004 through January 2005 was quite wet in places, so deeper soil moisture levels are still adequate if plant roots can reach these levels. In the last few weeks of May, though, conditions deteriorated enough to require a large swath from southwestern Michigan to central Missouri to be placed in the moderate drought category of the U.S. Drought Monitor map (Figure 4, National Drought Mitigation Center). The change in soil moisture state since February has been quite large (Figure 5, Climate Prediction Center), and well above normal amounts of rain will be required to ameliorate the situation.
 

A Dry Spring

March-April-May 2005 rain totals exceeded 9 inches in most of Kentucky, the Ohio Valley, Iowa, and southern Missouri, but barely scratched 5 inches in the central Midwest (Figure 6). Areas with less than 50% of normal spring precipitation exist in the D1 zone (Figure 7). Illinois had its 4th driest spring since 1895, with 1934 and 1936 being two of the three years with less rain than this year. Michigan had its 5th driest spring, and Missouri its 6th driest. In southern Missouri, West Plains has set a new record for the driest climatological spring, and Springfield had its second driest spring. Temperatures were near normal in much of the Midwest, although the eastern portion of the region reached several degrees below normal (Figure 8). There were large fluctuations in thermal regimes, however, with much warmer than normal conditions in early April, and several incidences of freezing in late April and early May. Despite the temperature changes, the season was also muted in terms of severe weather, with no killer tornadoes in May for the first time since 1992.