Midwest Weekly Highlights - November 10-16, 2004

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Mild Week in Mid-November

The week of November 10-16 was generally near or above normal in temperature throughout the region, due largely to persistent southerly flow around high pressure in the eastern U.S. The first few days of the period were stormy in the southern Midwest, as a low pressure system traveled across the region from west to east, depositing 1-2 inches of rain in southern Missouri, Illinois, and Indiana, and much of Kentucky (Figure 1). Meanwhile, the northern Midwest had some rain in the UP of Michigan, but was generally affected only by showers. Most of the northern Midwest received less than 50% of normal precipitation for the week (Figure 2), so no widespread amelioration of abnormal dryness was noted. Temperatures were near normal in the eastern Midwest, but where the southerly flow was more pronounced in the west, temperatures were 2-4°F above normal (Figure 3). Warming was much more intense in northern Minnesota, which was 6-10°F above normal for the week. The warm spell was intensifying at the end of the period, with high temperatures in the 60s all the way to the Iowa/Minnesota border (Figure 4), reaching 10-20°F above normal for the day.
 

Strong Ridge Over the Eastern U.S.

As the period began, a low pressure center entered the region from the southern Plains (Figure 5, College of DuPage - COD). However, unlike most lows at this time of year, it proceeded in a mostly easterly direction, not turning to the north at all as it crossed the Midwest. Vigorous rain storms entered the region south of Kansas City (Figure 6, National Weather Service - NWS), and the whole storm system took two days to pass through, resulting in almost all the rain for the week in the Midwest. By the 14th, a region of strongly above normal mid-tropospheric height had developed over the Midwest (Figure 7, Climate Diagnostics Center - CDC). This ridge was as strong as a typical late summer weather pattern (Figure 8, CDC), and protected the Midwest region from any influx of cold air from Canada for the rest of the week. Surface high pressure was sliding off to the Southeast by the 16th, accentuating the flow of warm and moist air from the Gulf of Mexico (Figure 9, COD). Because of the moisture, clouds and light showers were prevalent in the region. A widespread display of fog in the upper Midwest on the 16th (Figure 10, COD - "F" indicates fog) persisted past late morning and could be seen in visible satellite photos (Figure 11, COD). Without the clouds and fog, temperatures would have been much higher at the end of the period.