Midwest Weekly Highlights - November 16-21, 2006

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A Very Quiet Weather Week

The third week of November was rather tranquil, as large areas of high pressure dominated much of the weather. Temperatures this week exhibited a north-south gradient, with warmer conditions in the north, and cooler than normal conditions in the southern parts of the Midwest. Across Minnesota, northern Michigan, and Wisconsin, temperature departures this week ranged from 0°F to 4 °F above normal. Meanwhile, locations south of I-80 (generally), had temperature departures that were to 2 °F to 8 °F below normal, including southern Illinois, western Kentucky, and much of Indiana, Ohio, and Missouri (Figure 1).

The precipitation distribution during the third week of November exhibited a west-east gradient, with locations generally west of the Mississippi River seeing little precipitation, and location east of the River seeing much above average precipitation totals. Precipitation totals ranged from 0-10% of normal across a tremendously large area, including Wisconsin, Minnesota, Iowa, and northwest Missouri. In fact, parts of central Minnesota saw no precipitation at all during this period! On the other hand, locations such as Michigan, Ohio, Indiana, eastern Illinois and portions of Kentucky experienced 175-200% of normal precipitation (Figure 2). Most of this precipitation fell on the 16th of November, associated with a very intense low pressure system that barelled through the Midwest (Figure 3). Snowfall this week was light and sporadic, and existing snow depth from the big snow event last week in Wisconsin, Iowa, and Minnesota, had just about entirely melted by the end of the third week of November. The precipitation, however, fell in areas that are not experiencing drought, while locations that have been in drought since May, remain unchanged since last week (Figure 4)

 
Warmth Slowly Overspreads the Midwest

As one storm exited the region on the 16th, an upper level trough was carved into the Midwest (Figure 5), bringing a steady upper-level northwesterly flow and cool temperatures. A small perturbation embedded within the generally fast northwest flow aloft brought many locations in Wisconsin, Illinois, Michigan, and Indiana several chances for light rain, sleet, and snow over the two-day period of the 18-19th (Figure 6). No appreciable accumulation resulted from the squally-type weather. Thereafter, cool morning temperatures set in, with many locations seeing very heavy frosts on consecutive mornings. On November 20, Joplin, MO, set a new record low temperature of 21°F, breaking the previous record of 22°F set in 1964.

As the weak wave passed east, a large area of high pressure took control of the weather, resulting in nearly 100% sunshine across Illinois, Iowa, Missouri, Minnesota, and Wisconsin on the 20-21. Temperatures rebounded under the sunny skies to near normal levels, and then above normal levels on the 21st (Figure 7).

Will the warm weather last through the end of the month, or will cold air, currently bottled up in Canada, dislodge and dive southward? Find out in next week's edition of the Midwest Climate Watch.

 
Kruk