March 25-31, 2004
Midwest Weekly Highlights - March 25-31, 2004
March Ends With Heavy Spring Rains
The week of March 25-31 was dominated by a multi-day rain event associated with a very sluggish upper air pattern. Rain totals of 2-4 inches were widespread from southwestern Missouri to central Indiana, with more in some locations (Figure 1). All of Missouri, Iowa, Illinois, central Illinois, northern Ohio, and parts of Wisconsin and Michigan received more than 200% of normal precipitation for the week (Figure 2). A warm and humid air mass prevailed over the Midwest during most of the week, with temperatures 8-12°F above normal in the central and eastern Midwest and 4-8°F above normal elsewhere in the region (Figure 3). Some significant drought status improvement occurred in northwestern Missouri, although groundwater and farm pond conditions were still not recovered. The intensity of drought was reduced also in northwestern Minnesota and northern and central Wisconsin, as indicated on the U.S. Drought Monitor map (Figure 4, National Drought Mitigation Center). The rapid melt of a snow pack that close to normal for the first time in three winters, combined with heavy rain in places, resulted in some flooding in the northern tier of Minnesota and Wisconsin. Unfortunately, considerable dryness continued in most of Minnesota, where a grass fire burned 2000 acres in the east-central part of the state near Grasston, MN.
Week-Long Rain Event
During the week, substantial rain was observed in some portion of the Midwest on all seven days. On the 25th, a strong influx of warm humid air came in with a warm front, dropping rain across the southern edge of the Great Lakes (Figure 5, University Corporation for Atmospheric Research). As the morning began, a line of heavy precipitation moved west-to-east along the warm front, delivering copious rain (Figure 6, National Weather Service). The mid-troposphere flow was very zonal prior to the beginning of the period (Figure 7, College of DuPage), but by the 25th was beginning to develop a meridional tendancy in the West (Figure 8, COD). During the day, a surface trough of low pressure over the northern Great Plain intensified, and a surface low pressure center began to move eastward from the Great Plains. A cold front triggered an outbreak of thunderstorms overnight, and brought heavy rain to portions of eastern Iowa, northwest Illinois and southern Wisconsin by the morning of the 26th (Figure 9, UCAR). A second and stronger low formed over the southern Plains, and shifted northward during the day. A large area of precipitation broke out as a warm front reformed and pushed northward, triggering clusters of thunderstorms (Figure 10, COD) that trained over the same region. Precipitation totals in some locations exceeded 2-4 inches in some areas of central Missouri and east-central Illinois by the next morning (Figure 11, COD), and flash flooding was prevalent.
On the 27th, the upper level trough from the West coast entered the Great Plains region and started to amplify (Figure 12, COD). This limited the eastward movement of precipitation into the Midwest. However, a strong low pressure center under the trough in the central Plains (Figure 13, COD) did lift some strong convection into northwestern Missouri and western Iowa, resulting in very heavy rain totals by the morning of the 28th (Figure 14, UCAR). As the low pressure center moved across the northern Minnesota boundary, a sharply colder air mass entered the Midwest from the northwest (dashed temperature lines in (Figure 15, COD). A surface cold front extended from the northern to the southern edge of the Midwest began sweeping slowly across the region (Figure 16, COD). Some areas did receive more rain than others along the front due to favorable conditions under upper level disturbances, but the vast majority of the Midwest did receive a round of heavy precipitation by the morning of the 29th (Figure 17, UCAR) or the 30th (Figure 18, UCAR). Behind the main front, under an upper level low, a secondary convective band formed on the afternoon of the 29th in southwestern Missouri (Figure 19, NWS). While precipitation was not widespread, the region reported about 15 severe hail and 10 severe wind occurrences (Figure 20, Storm Prediction Center). Finally, the front passed to the east of the Midwest by the 31st, but considerable amounts of rain still fell underneath zones of instability rotating around the upper level low (Figure 21, UCAR).
Despite all the precipitation that fell during the March 25-31 period, river flooding was relatively restrained, with only a few rivers reaching the level of moderate flooding (Figure 22, US Geological Survey). A group of rivers in the Red River of the North drainage, including the Wild Rice River in Minnesota (Figure 23, USGS), reached well above flood stage due to rapid snow melt and heavy rain near the Minnesota border. In northern Wisconsin, the town of Antigo was flooded by Spring Brook due to the rapid melt of an above normal snow pack. The flood damaged almost 100 homes and 40 businesses, with at least one million dollars of damage estimated. One building was totally lost, but, fortunately, there were no deaths.