December 6-12, 2000

The week of December 6-12 started quietly but ended with a huge winter storm. Precipitation from the storm on the 11th and 12th resulted in a large swath of the central latitudes in the Midwest receiving above normal precipitation totals for the week (Figure 3). During the first half of the week, dry conditions prevailed, with only some of the lake effect precipitation belts receiving even 0.5 inches of water equivalent. Temperatures were quite cool in the northern Midwest (10 to 18°F below normal), but near normal in the southern Midwest. A quick moving clipper system passed through the area on December 8, depositing a few inches of snow in northern Illinois, Indiana, and Ohio, but not triggering enhanced lake effect snow. By December 11, though, conditions were perfect for the development of a strong Colorado low, including air mass conflict, upper level support, and moisture availability. This low dumped most of its Midwest snow on December 11-12, including a wide swath from south central Iowa through Lower Michigan which received up to 14 inches of snow (Figure 4). Intense cold and high winds followed the passage of a strong cold front associated with the storm, bringing the weekly temperature averages to more than 20°F below normal on the 12th (Figure 5).