Temperature and Precipitation Anomalies.

March was very dry and quite cool in the Midwest. All of the nine states of the region experienced below average precipitation totals and below average temperatures. The Midwest as a region had its 8th driest and tied for its 29th coolest March in 107 years. Most of the area north of the Ohio River received less than 1.5 inches of rain for the month (Figure 1a), which is 2 to 3 inches below normal (Figure 1b). Indiana had its 3rd driest and Michigan its 5th driest March ever. Only a small area of northern Missouri and southern Iowa received more than 100% of normal precipitation (Figure 1c). Negative temperature departures were largest in the western and southern Midwest (Figure 2), reaching 4-7°F over a large region. Iowa had its 15th coolest March, and Kentucky its 18th coolest. The cool conditions led to a substantial amount of March snowfall for western and northern portions of the region (Figure 3), helping to bring about river flooding in Minnesota, Iowa, and Missouri as the snow pack melted. The Ohio Valley, though, lost its snow pack early, and soils have become considerably dry due to the lack of precipitation in March. Toward the end of the month, this region was designated as abnormally dry by the U.S. Drought Monitor.

Extreme Events and Impacts.

The major impact event during the first week of March occurred in response to the previous month's heavy rains. Flooding along the lower Illinois river reached more than 8 feet over the flood stage of 14 feet at Beardstown, IL (Figure 18, USGS). However, far worse flooding occurred along the Rock River in northwestern Illinois due to a large ice jam that formed March 1. Large blocks of ice on the swollen river jammed against bridges and diverted water into several communities, including Cleveland, Barstow, and Osborn. The flooding was the worst since the summer of 1993 in this area. More than 150 people were evacuated by authorities, and many others fled on their own. Some of those saved were rescued from high ground by helicopters. Fortunately, no deaths or serious injuries resulted. The governor of Illinois made a state disaster declaration on March 1 for Henry and Rock Island counties, and is seeking to provide assistance to local governments.

The snow storm on March 11-12 guaranteed that the National Weather Service office near Des Moines, IA, would set a new record for the number of consecutive days with at least one inch of snow on the ground. The old record of 90 days was surpassed on March 11, and the new record continued to accumulate until it reached 99 days on March 20, when the snow pack melted away late in the day. In addition, Rochester, MN, and La Crosse, WI, set new records for one-day snowfall on March 12, receiving 8.6 and 7.5 inches of snow, respectively. Minneapolis experienced the usual winter snow storm delays in transportation, but the airport stayed open. Another heavy and somewhat surprising snowfall on March 15-16 led to a slew of accidents on area highways, closed schools in Missouri and Iowa, and caused flight delays of over two hoursat O'Hare Airport in Chicago. Windy conditions caused blowing and drifting of snow across highways, especially in Iowa and northern Illinois. Des Moines, IA, set a new record for snowfall on March 16 of 3.1 inches, which was on top of 2.0 inches that fell on the previous day.

The heavy rain that occurred on March 14-15 (prior to the second snow event) caused widespread flooding in northern Missouri and southern Iowa, as already saturated ground speeded runoff to local streams and rivers. The Grand River near Sumner, MO, reached almost 35 feet, which is almost 9 feet above the flood stage of 26 feet (Figure 19, USGS). Ironically, the snow and cold weather that followed gave the region a temporary reprieve, slowing runoff and preventing further snow melt in Iowa. However, much of the Upper Mississippi drainage is now in a precarious situation regarding flood potential, which is higher than normal due to saturated grounds and much more snow water equivalent on the ground than is normal (Figure 20, NOAA). In fact, the Mississippi already reached above flood stage in a number of locations north of St. Louis at this time. More than 5000 acres of crop land were flooded along the Mississippi at Chariton, IA. Finally, the Red River valley in northwestern Minnesota is also poised for flooding. Only a very fortuitous combination of slow melt and below normal precipitation will prevent damaging flooding from happening. Temperatures did moderate enough before the frontal passage to end a record setting consecutive streak of 145 days below 60°F at Champaign, IL, the location of the MRCC. This run, from November 5, 2000 (61°F) to March 31, 2000 (62° F), exceeded the previous record run by 20 days.

Abnormal Dryness in the Midwest.

The most recent 90 days have been very dry in the Ohio River Valley, with deficits approaching 5 inches in some places (Figure 21). The dryness is especially acute in southern Illinois, much of Indiana, and southern Ohio, and is reflected in both top soil moisture levels (Figure 22) and stream flow (Figure 23, USGS) being well below normal in these locations. During the last week of March, the U.S. Drought Monitor placed a large swath of the Ohio Valley and parts of southern Illinois and southeastern Missouri into category D0, reflecting their abnormal dryness (Figure 24), National Drought Mitigation Center). There is not yet any strong concern for agriculture, as subsoil moisture is adequate, but this trend will be followed closely in April. A dry April would place the eastern Midwest into a zone of concern about potential drought similar to last spring.

While one part of the Midwest worries about potential flooding, the Great Lakes user community is worried about the decline of lake levels continuing this year. Levels in Lake Michigan-Huron are 22 inches below normal, which is a few inches less than last year at this time (Figure 25, NOAA). This is still about 9 inches above the all-time low measured during the mid-1960s multi-year drought in the region. Lake specialists report that the cold weather of December 2000 enhanced evaporation due to the large temperature gradient between the air and the lake surface. While some of this evaporated water falls in the Great Lakes drainage basin as lake-effect snow, much of it leaves the region. Just as the lakes were finally cooling down to freezing in late December, the weather returned to normal or even above normal temperatures, and much of the lake surface in the Michigan-Huron system that normally freezes over did not during January-February 2001. The open lakes continued to evaporate at an above normal rate, often without the benefit of depositing snow nearby.

As the lower lake levels persist into the warm season, they will affect port access by lake freighters, requiring loads to be lessened to allow enough draft to enter certain ports. In addition, pleasure craft will also have problems maneuvering in near-shore environments. There are also public heath issues, such as enhanced bacteria growth in shallow, warmer waters with less dilution, and storm waves stirring up polluted sediments. The few benefits, such as a reduction in shoreline erosion, wider beached, and enhanced growth of plants in the near shore areas, do not outweigh the difficulties further lake lowering may cause. The only positive note is that the Climate Prediction Center has indicated an enhanced chance for above normal precipitation in the area late in the spring.