February 22-28, 2007
Midwest Weekly Highlights - February 22-28, 2007
Cold and Stormy
The month of February closed with colder than normal temperatures over the central portions of the Midwest and plenty of precipitation. Temperatures the last week of the month continued below normal across areas that still had snow on the ground, but averaged 1°F to 4°F above normal across southwestern Missouri and northern Minnesota and Wisconsin (Figure 1). The greatest departures below normal, ranging from -6°F to -2°F were found in a band from eastern Ohio back west and then northwest through Iowa, where snow cover was present for much of the week (Figure 2).
There was significant precipitation this last week from two strong storm systems. Precipitation was normal to well above normal generally northwest of the Ohio River (Figure 3), with amounts as much as seven times normal over parts of Iowa. Much of this precipitation came as freezing rain, sleet, and snow over the northern half of the region (Figure 4). It remained dry across portions of the eastern Midwest, including southeastern Kentucky. Abnormally Dry conditions, as depicted on the U.S. Drought Monitor, have expanded further into Kentucky (Figure 5). Precipitation this week will forestall any worsening of drought conditions in northern Minnesota and Wisconsin.
The "B" Word
Two major winter storms hammered the Midwest this week, producing a mix of wintry precipitation across the northern half of the region and rain over parts of the southern half. The first storm began to intensify in the lee of the Rockies on February 23, and in anticipation a variety of winter weather-related watches and warnings covered the northern half of the Midwest (Figure 6). In the morning of February 24 the low was gathering strength over west-central Kansas (Figure 7). A large shield of precipitation was spreading northeast through Missouri and Iowa, and by afternoon had pushed northeast through central Illinois and southern Indiana. Initially, freezing rain and sleet developed on the southern edge of the precipitation shield from Iowa across northern Missouri into central Illinois. Heavy freezing rain and sleet occurred throughout southern Iowa, with thunder and lightning reported with the freezing and frozen precipitation at times. North of the freezing rain and sleet, heavy snow was falling over southern Minnesota, southern and central Wisconsin, and northern Illinois. Wind speeds increased as the low pressure system deepened, and by mid-afternoon on February 24 winter storm warnings covered Iowa, much of Minnesota, Wisconsin, and lower Michigan, and blizzard warnings were in effect for southeastern Minnesota, northeastern Iowa, and southern Wisconsin (Figure 8).
Aftermath
The slow-moving storm weakened and finally moved out of the region on February 26 (Figure 9). In its wake the storm left more than two feet of snow on the ground across southern Minnesota, ice from one-half to one inch thick coated central and southern Iowa, and heavy rain combined with melting snow and frozen ground prompted flood watches and warnings from Iowa southeast through Illinois and Indiana.
A number of locations in Minnesota and Wisconsin set new daily and storm total snowfall records. La Crosse, WI received 21.0 inches of snow from the storm, the largest storm total ever recorded. This broke the old record of 19.1 inches set on March 12-14, 1997. Snowfall records in La Crosse date back to 1893. Duluth, MN set both a daily precipitation record and daily snowfall record on February 25. Precipitation total 1.06 inches, shattering the previous record of 0.28 inches set in 2000. Snowfall totaled 11.3 inches, breaking the old record of 4.1 inches set in 2001. A new daily snowfall record was also set at Eau Claire, WI, where 6.2 inches on February 25 broke the old record of 3.0 inches in 1994. St. Cloud, MN received 7.6 inches of snow, breaking the old daily record of 4.8 inches in 2001.
The heaviest snow fell in southeastern Minnesota and southwestern Wisconsin (Figure 10, NWS La Crosse WI). Winona, MN recorded a whopping 29.5 inches of snow from the storm, and amounts in excess of two feet were reported throughout Winona County. Winona, MN piled up 29.5 inches, Dakota, MN 26.0 inches, and Galesville, WI (Trempealeau County) also had 26.0 inches.
While the western portions of Wisconsin received the heaviest snow, significant snow occurred across south central Wisconsin (Figure 11, NWS Sullivan WI). A foot or more fell on much of the southern half of Wisconsin and locations near Madison and Milwaukee reported up to 18 inches of snow.
While the impacts of the heavy snow and high winds were significant, the most damaging aspect of the storm was the heavy freezing rain that occurred in central and eastern Iowa. Ice accumulations ranged from 0.75 to 1.50 inches, with some amounts reported as high as 2.00 inches. The ice along with the high winds generated by the low pressure system brought down trees and power lines and made travel impossible. As of late February 25, and estimated 200,000 Iowans were without power, and estimates were that it could be a week before power was restored to some areas. Livestock producers reported a critical need for generators to supply power for heating, ventilation, and water. On February 27 an estimated 100,000 Iowa homes were still without power, and 60 counties had been declared disaster areas. In the meantime, residents of Iowa, Minnesota, and Wisconsin were bracing for yet another winter storm.
Heavy rain in central and southern Illinois, Iowa, and Indiana combined with frozen ground and melting snow (in areas still with snow on the ground), raised the flooding potential, and flood warnings were issued for a number of rivers in all three states.
Another Storm Targets the Midwest
Even as recovery from the February 23-25 storm was underway, another strong storm system began to take shape in the lee of the Rockies on February 28. Winter weather watches and advisories were posted for the northern half of the Midwest in anticipation of storm intensification, and flood watches covered the northeastern two-thirds of Illinois (Figure 12). The Storm Prediction Center upgraded the afternoon convective outlook to include a Moderate Risk of severe weather across central and southwestern Missouri (Figure 13). Strong winds in the circulation of the developing storm were expected to create favorable conditions for supercells and possible tornadoes.
Thunderstorms developed during the afternoon in Kansas and moved eastward into Missouri after dark (Figure 14). These supercells produced several tornadoes in Kansas and Missouri and destroyed at least two houses and caused some structural damage. Storm reports included large hail as well, with 2.75 inch hailstones reported near Amsterdam, MO in Bates County. Heavy rain from the thunderstorms caused flash flooding in the Kansas City area.
The low pressure system continued to intensify and head northeast toward Iowa. Eastern Missouri, the southern half of Illinois, southwestern Indiana, and western Kentucky were placed in a Moderate Risk for severe weather on March 1, while the northern Midwest was bracing for another onslaught of winter weather.
SDH