April 2008
Midwest Overview - April 2008
The Ying and Yang of April Weather in the Midwest
There was a marked difference in both temperature and precipitation across the Midwest during April 2008, but patterns for both were very similar. Along a line from northeastern Wisconsin to northwestern Illinois to central Kentucky, average daily temperatures were near normal, rising eastward to as much as 5°F above normal in northeastern Ohio (Figure 1). West of the aforementioned line, temperatures were below normal during the month. The largest departures of 3°F to 5°F below normal occurred from Minnesota south through the western halves of Iowa and Missouri. It was the second week of April before temperatures in the 70s occurred across much of the region.
Precipitation was 150 to 200 percent of normal from southern Missouri northward through the eastern half of Iowa, Wisconsin, northern Minnesota, and the Michigan UP. In contrast, precipitation was 60 to 75 percent of normal for the month from eastern Illinois through most of Indiana, Ohio, and southern lower Michigan (Figure 2). Areas of above normal precipitation coincided closely with the colder areas of the Midwest in April, and the drier areas with the warmer eastern Midwest. The period February through April 2008 was the wettest on record for the Midwest region, with an average 11.64 inches of precipitation. This was also the wettest February-April for Missouri with 18.92 inches, and for Illinois with 14.32 inches. The continuation of wet weather rapidly improved dry conditions across the Midwest, and the April 8 U.S. Drought Monitor marks the first time since the second week of May 2005 there was no D1 (Moderate) drought depicted in the Midwest.
April snowfall was seven times normal across much of Minnesota, and two to three times normal across the northern half of Wisconsin and the Michigan Upper Peninsula (Figure 3). At the end of the month there was still more than 4 inches of snow over much of northern Minnesota, and more than a foot across the Arrowhead (Figure 4).
Heavy Rain, Severe Weather
The wet weather pattern over the southern Midwest in February and March continued into the first half of April. On April 3 and April 4, two to four inches of rain fell from the Missouri Ozarks into western Kentucky, southern Illinois, and southern Indiana, with isolated amounts in excess of 6.50 inches. The heavy rain caused another round of flash flooding and road closures in these areas, and exacerbated flooding already in progress on rivers and streams. The flash flooding resulted in one death in Kentucky.
On April 8-10 another strong spring storm moved through the Midwest on a more northerly track. This storm dropped another 3 to 4 inches of rain on southwestern Missouri, and one to three inches of rain in a band from northwestern Missouri into southeastern Iowa (Figure 5). In the period between February 10 and April 10, 16 to 20 inches of precipitation accumulated across the southern third of Missouri, far southern Illinois, and far western Kentucky, two to three times normal (Figure 6). Thunderstorms dropping up to 4 inches of rain in 12 hours caused widespread flash flooding across central and eastern Iowa on April 25.
This weather system also produced the first significant severe weather outbreak in April. There were 26 reports of tornadoes on April 10, 24 of these in Iowa. Two tornadoes also touched down in Kentucky on April 11 as the cold front trailing from the strong low pressure system marched east. Severe storms swept across the Midwest again on April 23-25 as yet another strong cold front pushed through the region. A tornado touched down near Wyocena, WI damaging homes, destroying barns, and knocking out power to hundreds of homes. Grapefruit-size hail (4.25") was observed near Tomahawk, WI with another thunderstorm.
The Snow Won't Quit
The northern Midwest made up for lack of snow early in the season as four weather systems dropped heavy snow on the region. On April 1, 8 to 10 inches of snow piled up in the central Michigan UP, with 18 to 24 inches in Marquette County. A few days later, a small but strong wave of low pressure produced a narrow band of heavy snow from eastern North Dakota across the Iron Range of northern Minnesota . Snowfall amounts across northern Minnesota were generally in the 6 to 12 inch range, but portions of St. Louis County received more than two feet of snow. 26 inches were reported in Babbitt, MN, and 32 inches accumulated near Virginia, MN. This was the largest ever April multi-day snowfall in the Iron Range. The heavy wet snow caused trees and powers lines to snap, resulting in power outages to thousands of customers. In northeastern Minnesota additional travel problems occurred as the snow became mixed with sleet and freezing rain.
Heavy snow with blizzard conditions affected Minnesota and Wisconsin on April 11. Snow accumulated 6 to more than 14 inches in northeastern Minnesota, northern Wisconsin, and the Michigan UP, with 16.9 inches reported near Askov, MN (Pine County). Winds gusting in excess of 40 mph toppled trees and power lines from northeastern Minnesota into northern Wisconsin. Duluth International Airport recorded a wind gust of 62 mph, with a few other locations reporting gusts over 50 mph.
The final snows occurred near the end of April. A surface low pressure system associated with another strong upper level trough swinging through the Midwest pulled unseasonably cold air into much of the Midwest beginning on April 25. Eight to as much as 18 inches of heavy, wet snow fell from eastern South Dakota through western Minnesota. A second upper low crossing the Great Lakes brought 3 to 6 inches of snow to portions of central Wisconsin, with lighter amounts east through Michigan.
Flooding
The combination of snow melt and heavy rain resulted in continued flooding of rivers and streams throughout the northern half of the region during April, particularly in northern Illinois and southern Wisconsin (Figure 7). At the end of the month major flooding was occurring on the Mississippi River between Rock Island, IL and Burlington, IA. Moderate flooding was occurring on some rivers in Iowa, northern Illinois, and southern Wisconsin (Figure 8).
-SDH-