Midwest Weekly Highlights - March 18-24, 2004

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A Dry Week in Most of the Midwest

The week of March 18-24 was drier and cooler than normal, with a return to warmer and moister condition only during the last day of the period. Precipitation was scattered, with only eastern Iowa/Northern Illinois and parts of the southern and eastern Midwest exceeding 1 inch of rain (Figure 1). The far northern and western edges of the Midwest were driest, with precipitation less than 25% of normal for the week (Figure 2). Temperatures for the first 6 days of the period moved up and down with the passage of two cold fronts, so despite a warm end to the period, the western third of the Midwest was only 2-4°F above normal for the week, while most of the eastern Midwest was 1-3°F below normal (Figure 3). Maximum temperatures on the 24th were more than 10°F above normal in most of the Midwest. Drought in Minnesota continued in the US Drought Monitor issued for March 23 (Figure 4, National Drought Mitigation Center).

Big Changes at the End of the Week

A cold front raced through the Midwest at mid-week, bringing one last pulse of very cold Canadian air to the northern Midwest. Low temperatures on the morning of the 22nd reached well below zero in parts of the northern Minnesota, Wisconsin, and Michigan (Figure 5). Marquette, MI, set an all time low temperature record for the date of -16°F, exceeding the previous record by 7°F. On the 24th, high pressure moved into the southeastern U.S. (Figure 6, College of DuPage) and a strong southwesterly flow brought a warm front northward into Minnesota, Wisconsin, and Michigan. A plume of air with dew points in the 50s reached the western Midwest by the evening (Figure 7, COD). Supported by a strong low-level jet reaching 40-50 knots over the Midwest (Figure 8, COD), maximum temperatures for the day were in the 60s and 70s over most of the Midwest, and even reached the 80s in western Iowa (Figure 9). This represents a change of 50-60°F between the morning of the 22nd and late afternoon of the 24th. A strong line of storms formed along the warm front during the morning of March 24 (Figure 10, NWS), dropping 2-4 inches of rain in some places in northern Illinois (Figure 11, NWS). More precipitation occurred overnight and will be reflected in the totals for the last week of the month.