Midwest Overview - April, 2006

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A Warm Month

Temperatures during April varied from the very warm to the very cool, not all that unusual for spring in the Midwest.  The warmest areas were the northern and southern thirds of the region, where temperatures ranged from 4°F to 6°F above normal, although parts of northern Wisconsin and Minnesota were as much as 7°F above normal (Figure 1).  Across the central third of the Midwest temperatures were 3°F to 4°F above normal.  Although for the month temperatures were warmer than normal, slow moving low pressure systems produced a few periods of cloudy, cool, and wet weather in the western half of the region. The warmest period of the month was the second week of April when record temperatures were set as afternoon highs reached the low 90s in western Missouri and mid 80s in Minnesota. On the opposite side of the coin, several slow moving low pressure systems near the end of the month produced widespread rain and cloudiness which kept temperatures cooler than normal in the western portions of the region.


Drought-Affected Areas Receive Beneficial Rain

Those same slow-moving weather systems produced significant rainfall across the western half of the Midwest.  The most rain fell in south-central Minnesota and northern Iowa, southwestern Missouri, and eastern Kentucky (Figure 2).  Monthly rainfall exceed six inches in some locations.  The driest portions of the Midwest in April were north-central Wisconsin, where rainfall was less than 50 percent of normal, and the mid-Mississippi River Valley from Quincy, IL south through the Missouri bootheel (Figure 3).  By the end of April there was a significant reduction in drought conditions over Illinois and southeastern Missouri.  Effects from the heavy rain in western Missouri through Minnesota during the last two days of April will be reflected in the the May 4 edition of the U.S. Drought Monitor.


Severe Weather on Record Pace

April was a very active month for severe weather in the Midwest.  Severe weather (tornado, hail 0.75 inch or larger, thunderstorm winds 58 mph or greater) was reported on 20 days in April somewhere in the nine-state Midwest region.  The most widespread outbreak was on April 2, when tornadoes touched down in Iowa, Illinois, Missouri, Indiana, and Kentucky, and there were hundreds of high wind and hail reports (Figure 4).  The storms resulted in one fatality in the St. Louis Metro area.  On April 13 a smaller (in areal extent) but more damaging outbreak occurred from Iowa into Illinois. A tornado rated F2 on the Fujita scale ripped through Iowa City, IA during the evening hours, causing extensive damage to downtown and the University of Iowa campus, and caused an estimated 30 injuries. One woman was killed near Nichols, IA when a tornado struck her mobile home.

Statistics from the NOAA Storm Prediction Center based on preliminary reports, show that through the end of April there have been 604 tornado reports this season, more than twice normal (Figure 5, SPC).  Of the 16 killer tornadoes this year in the U.S., six have occurred in Missouri, with one each in Iowa and Illinois.