December 8-14, 2007
Midwest Weekly Highlights - December 8-14, 2007
Winter's Icy Grip
Waves of low pressure moving along a frontal boundary stalled across the central Midwest brought freezing rain to large portions of the region during the first half of the week.
The mean position of the frontal boundary was evident in the huge gradient in temperature departures for the week. Average daily temperatures ranged from 12°F below normal in northwestern Minnesota to 15°F above normal in southeastern Kentucky (Figure 1).The freezing rain fell generally north of the 0°F departure line.
Precipitation this week was abundant over the southern two-thirds of the region, ranging from 200 to 400 percent of normal (Figure 2). Most of this was rain or freezing rain, with significant snow limited to Iowa, southern Wisconsin, parts of northern Ohio, and the Michigan Upper Peninsula (Figure 3). In sharp contrast, the northern third of the Midwest received from zero to less than 25 percent of the normal precipitation for the week. The rain this week in the southern Midwest wiped away any remnants of abnormal dryness in Indiana and Ohio, and significantly reduced the area of dry weather in Missouri on the latest U.S. Drought Monitor (Figure 4). Extremely dry conditions continued to persist in far southeastern Kentucky, however.
Encased in Ice
On December 8 cold air was settling south over the Midwest while a low pressure system organized over the southern Rockies. By sunrise rain and some freezing rain were falling across the southern portion of the region, spreading northward during the day. Light icing occurred from central Missouri across central Illinois with this wave, but precipitation amounts were generally light early in the day. A second wave of low pressure developed and moved along the stalled frontal boundary on December 8 to the early morning of December 9, producing more substantial rain (Figure 5). Portions of southwestern Missouri received upwards of 1.50 inches of rain, and much of this turned to ice as it made contact with objects near the surface. Up to a half inch of freezing rain fell by the morning of December 9 in western Illinois, and thunder was heard with some of the heavier cells from Missouri into eastern Illinois.
On December 10 scattered areas of freezing rain and sleet occurred well north of the frontal boundary (Figure 6), with heavier rain occurring along and just north of the boundary in the warmer air (Figure 7). A few locations in southern Wisconsin reported up to 1.5 inches of sleet. Some freezing rain and drizzle again accumulated from northeastern Missouri into northern Illinois. The frontal boundary began a northward return on December 11, and forecasters expected a broad swath of icing to occur from Kansas through northern Illinois as moisture-laden air was drawn up across the frontal boundary (Figure 8,Figure 9). A strong surge of warm air pushed to the Ohio River Valley. High temperatures that day reached the upper 60s and lower 70s along the Ohio River (Figure 10), and daily records were set in a number of locations (see table below). In the cold air north of the front, freezing rain coated areas from central Missouri into west-central and northern Illinois, south-central and southeastern Wisconsin, and in southern lower Michigan (Figure 11). For some parts of Missouri, Iowa, and northwestern Illinois, this marked the fourth consecutive day with some freezing rain. Temperatures over the southern half of the Midwest finally struggled above freezing late in the day south of a line from Kansas City, MO to Traverse City, MI.
The worst areas of damage in the Midwest from the ice were in Missouri, southern Iowa, and western Illinois, where trees and power lines broke under the weight of as much as 1.5 inches of ice (ice accumulation map). More than 200,000 utility customers lost power in Missouri, 60,000 in Iowa, and 13,400 in Illinois at the peak of the storm on December 11. As of December 14, 30,000 customers in Missouri were still waiting for power to be restored. A number of deaths were reported due to the ice throughout the region, mostly as a result of traffic accidents.
Heavy Rain Causes Flooding Concerns in Kentucky, Ohio
Rain continued to fall in the Ohio Valley on December 12-13. On December 13 the last in the series of low pressure systems moved through the lower Midwest, and a shield of rain extended north through Kentucky, Indiana, and Ohio (Figure 12). Rainfall this week in Kentucky ranged from two to four inches, with some locations over five inches (Figure 13). Woodbury, KY (Butler County) recorded 7.00 inches of rain for the week. One to two inches of rain fell over most of Ohio, bringing totals for the week to as as much as 3.50 inches in southeastern Ohio. Flood watches were issued for much of Kentucky and for southeastern Ohio as rivers and streams rose due to the runoff from the rain and as another major winter storm began to gather strength in the Southern Plains (Figure 14). At the end of the week the Blanchard and Maumee Rivers in Ohio and the Kankakee River in western Inidiana were at or above flood stage.
SDH