Midwest Weekly Highlights - October 18-24, 2006

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Quiet but Cold

A broad trough of low pressure dominated the upper level flow this week (Figure 1), maintaining the supply of cold air to the Midwest. That meant a continuation of below normal temperatures, but only light to moderate precipitation.

There was a distinct west-to-east temperature gradient across the region this week. Temperatures ranged from 2°F to 3°F below normal in eastern Ohio to 11°F to12°F below normal in western Iowa and Minnesota (Figure 2).  Freezing temperatures again reached as far south as the Ohio River, with the coldest air over Missouri on the morning of October 24 (Figure 3).

Precipitation was heaviest in a band from western Iowa across northern Illinois and into lower Michigan, and across much of Ohio (Figure 4).  Significant precipitation occurred in parts of the drought areas in Missouri and Iowa (Figure 5), but dry weather continued across most of Minnesota and Wisconsin. This weekly summary is the first since mid-March to not to report severe weather somewhere in the Midwest during the period.


Touched by Winter...Again

As the week began, one major weather system was departing the eastern Midwest while another less potent system was beginning to enter the western portions of the region. Snow advisories were posted for parts of northwestern Iowa for the early morning hours of  October 18 as moisture with the approaching system overran the cold air still in place over the Midwest. Some snow did accumulate on grassy surfaces, but warming temperatures quickly melted it away after sunrise. This system brought light rain to the central Midwest as it moved through.

Temperatures over the southern half of the region recovered to the upper 50s to mid 60s between weather systems, but the mild weather was short-lived. High pressure ridging into the Midwest cleared skies on October 20 and provided welcome sunshine to the central and southern Midwest, but already two weather systems were setting up to bring another shot of winter weather to the Midwest. Low pressure developing in the Southern Plains and a low spinning over Hudson Bay combined to bring a one-two punch of rain and much colder weather to the region (Figure 6). A swath of rain amounts from 0.30 to 0.80 inches fell from western Missouri across southern Wisconsin, northern Illinois, and lower Michigan during the later afternoon and overnight hours of October 21 (Figure 7). By the morning of October 22 much colder air was spilling into the Midwest behind the system, with snow and snow flurries occurring in the wake of the storm. Madison, WI set a new daily snowfall record on October 21 with 2.3 inches, breaking the old record of 0.2 inches in 1917. On October 23 the cold northwesterly flow over the open waters of the Great Lakes produced lake effect snow in Minnesota, Wisconsin, Michigan, and Ohio (Figure 8). Amounts were generally light, but Hurley, WI (Iron County) received 6 inches of snow. Amounts in Van Buren County, MI ranged from 1 to 3 inches, northwest lower Michigan 1 to 2 inches, and in Ohio 1.5 to 3.5 inches fell in Geauga County.

 SDH