Midwest Weekly Highlights - March 18-24, 2009
Mild and Dry for Most of the Week
Temperatures across most of the Midwest were well above normal this week, ranging from 1°F to 5 °F above normal in Ohio to 9°F above normal in central Iowa (Figure 1). Only the far northern and far northeastern portions of the region were near normal this week. The first two days of the week were much colder than normal in northern Minnesota as a large high pressure system drifted over the central and eastern United States. Low temperatures dropped into the single digits and teens on March 19 from northern Minnesota across northern Wisconsin where there was still snow on the ground. In contrast, record high temperatures were recorded in southern Minnesota and the other eight Midwestern states on March 18, with a few additional high temperature records on March 19.
Precipitation was well below normal over the eastern half of the region and well above across the western half (Figure 2). Much of the week was dry, but a major storm in the Central Plains brought precipitation to most of the region at the end of the week. Rain did move into Indiana, Ohio, and Kentucky on March 24, but that rainfall will be reflected in next week's totals. The U.S. Drought Monitor for March 24 depicted Abnormal Dryness in southeastern Ohio and eastern Kentucky. Moderate to Severe drought continued to persist from southeastern Minnesota to the northern half of Wisconsin to the western Michigan U. P. (Figure 3).
Snow depths of four or more inches still remained across northern Minnesota, northwestern Wisconsin the Michigan U. P. and northern Lower Michigan at the end of the week (Figure 4). The deepest snow cover was over the Arrowhead of Minnesota and the eastern U. P. of Michigan.
Winter Weather in the Northern Midwest
Precipitation broke out across Minnesota, Wisconsin, and Michigan on March 20 as a upper level wave dove south out of Canada into the upper Midwest. Much of the precipitation was snow, by the morning of March 21, one to four inches of new snow was on the ground from northeastern Minnesota across to northern Lower Michigan (Figure 5). A few locations along Lake Superior received up to 7 inches of snow. In southwestern Missouri, showers and thunderstorms developed along a weak trough of low pressure, bringing 0.25 to 0.75 inches of rain to the western Ozarks. In far southwestern Missouri several locations measured more than an inch of rain.
Major Spring Storm Spins Up Over Northern Plains
On March 22 a large upper level trough was coming ashore in the western U.S., (Figure 6) and a surface low pressure system was developing over central Montana. As the upper trough moved over the Rockies a closed low developed over western Nebraska and the system slowed to a crawl. The surface low intensified over the Dakotas, pulling cold air south from Canada and warm air northward from the Gulf of Mexico. A variety of watches, warning, and advisories were issued for the central U.S., ranging from high wind advisories and warnings from Texas to Iowa, ice storm warnings for the Arrowhead of Minnesota, and blizzard warnings and tornado watches for the Dakotas (Figure 7). Freezing rain fell from northern Minnesota to north central Wisconsin early on March 23.
By the late afternoon of March 23 the low pressure system was still spinning over central Nebraska (Figure 8). Severe thunderstorms developed in the Central Plains during the afternoon of March 23, and some moved into western Iowa and Missouri. A total of five tornadoes touched down in southwestern Iowa as the storms passed through evening. The most significant was an EF-2 rated storm in Harrison County to the west and northwest of the town of Missouri Valley. This tornado produced damage along a nine-mile path. Damage included two semi-trailer trucks being overturned on Interstate Highway 29, a single family home destroyed and 54 empty rail cars derailed. Another tornado caused leaking anhydrous ammonia tanks in in Cass County. Thunderstorm winds caused damage in both Missouri and Iowa, with an 81 mph gust clocked near Spencer, IA (Clay County). Some showers dotted the region as far east as Indiana, but most of the precipitation held off until March 24.
Heavy Rain and Scattered Severe Weather
There were only scattered severe thunderstorms in the Midwest on March 24 in Missouri and Illinois. During the morning 2.75 inch hail was reported in Johnson and Bates counties in Missouri. Additional severe storms occurred during the afternoon and evening as the frontal system moved east. Most of the storms produced only minor wind damage. Heavy rain was the problem in Missouri, Iowa, Minnesota, and Illinois. Heavy precipitation fell over much of Minnesota, with some of the heaviest over the Red River Valley (Figure 9) In Iowa, the heaviest precipitation fell from March 22 to early on March 24 in a wide band from south central into north central Iowa (roughly along Interstate 35) where amounts of around two inches were common (Figure 10). These rains pushed river levels to near or a little above flood stage over much of the state. Fortunately this widespread rain followed about 12 days of dry weather, thus preventing more significant flooding. Rainfall from this system on March 24 ranged from 0.50 to 1.50 inches across much of Missouri, Iowa, western and southern Illinois and western Kentucky (Figure 11). A band of heavy rain ranging from 2.00 to almost 3.00 inches occurred from southwestern Missouri to northern Illinois. Flash flood warnings were issued for a number of counties in southwestern Missouri in the morning and in eastern Missouri in the afternoon. Rainfall rates of more than two inches per hour reported in some areas.
In the Arrowhead of Minnesota, freezing rain caused extensive damage to trees and power lines in Lake County in the North Shore communities. Power was out to at least 2,800 customers of Lake County Cooperative Power & Light.
Strong gradient winds of 40 to 50 mph produced by the intense low pressure system caused scattered damage across Iowa and Illinois.
Red River in Minnesota and North Dakota was in major flood this week. Minnesota state agencies were prepared to activate emergency operations center on St. Paul to coordinate state and federal flood assistance. By the afternoon of March 23, 300 National Guard were activated to provide flood relief in northwestern Minnesota. Moderate to major flooding was occurring on the Red River on the morning of March 24 (Figure 12), and the river was expected to reach record levels later in the week, surpassing marks set in 1997.
River levels remained high in other locations in the Midwest, most notable the lower half of the Illinois River (Figure 13) and the Kankakee river in western Indiana (Figure 14). A general decline in river levels was forecast, although they are expected to stay near or above flood stage with addition of the rain at the end of the week.