Midwest Weekly Highlights - February 22-28, 2009

Quiet Start

This week started much like the previous week, with a large high pressure system settling in over the Midwest. Temperatures the last week of February were below normal across the region, ranging from 3°F to 6°F below normal in the southern two-thirds of the region to 10°F to 16°F below normal across the northern third (Figure 1). The largest departures were found over the northwestern half of Minnesota.

Precipitation was generally heavy across the northern half of the Midwest, and in the Ohio Valley. Precipitation for the week was 200 to 400 percent of normal from northwestern Iowa/southwestern Minnesota eastward through lower Michigan (Figure 2). Most of the precipitation on the northern third of the Midwest fell as snow, and snowfall for the week was generally two to three times normal (Figure 3). At the end of the week the deepest snow cover existed across the northern half of Minnesota eastward into northern lower Michigan. Snow depths generally ranged from 10 to 20 inches, but were as much as 36 to 52 inches over the eastern Michigan U. P. (Figure 4).

The heavy precipitation this week was welcome across central and northern Wisconsin, which is still experiencing Moderate to Severe drought as depicted on the February 24 U.S. Drought Monitor (Figure 5). Precipitation for Wisconsin for the winter season (December-February) was near to three inches above normal in the southeastern half of the state, to normal to one inch below in the northwestern half (Figure 6).
 

Stormy End

Up to six inches of snow fell in eastern Kentucky February 22 on the heels of the storm the came through the region on February 21. That was followed by a large area of high pressure which brought fair but cold weather to the Midwest. The quiet weather did not last long. By February 25 the axis of high pressure extended along the east coast and the Midwest was being squeezed between a cold from approaching from the north and low pressure developing over Texas (Figure 7). Strong southerly winds brought warmer air and Gulf moisture into the Midwest ahead of these systems, with temperatures climbing into the 60s as far north as Illinois. Showers and heavy thunderstorms developed in the warm moist air, and Severe thunderstorm watches were issued in anticipation of heavy storms. The heaviest storms concentrated in a band from northern Illinois into central lower Michigan (Figure 8). Rainfall in this band ranged from 1.50 to more than 2.50 inches, with isolated amounts to 3.00 inches (Figure 9). Severe storms were reported most in Iowa, Missouri, and Kentucky on February 26. North of the frontal boundary, freezing rain fell on southern Wisconsin, causing numerous travel problems. Further north from central Minnesota across northern Wisconsin to lower Michigan 6 to 10 inches of snow piled up (Figure 10).

Blustery, sharply colder weather followed this system as it moved into the eastern Great Lakes (Figure 11). Light lake-effect snow continued eastern Wisconsin and northeastern Illinois, with occasional flurries further south. After a brief taste of spring-like weather, most of the region was experiencing temperatures 10°F to 25°F below normal (Figure 12). Temperatures dropped well below 0°F from Minnesota to Michigan, with record lows of -20°F to -28°F from northern Wisconsin across northern Michigan.
 

Snow Swipes Western Missouri

An inverted trough of low pressure extending northwest from another wave along the cold front brought heavy snow to the southwestern half of Missouri late on February 27 and through February 28 (Figure 13). Snowfall generally ranged from 3 to 6 inches, with as much as 7 to 9 inches of snow accumulating in the central Ozarks (Figure 14).
 

Minor Flooding

The heavy precipitation and snow melt contributed to rising water levels on some rivers in the northern Midwest at the end of the month. Minor flooding was reported on the Illinois River and on the Kankakee river in northern Indiana. Minor flooding was also reported on a few small streams in northwestern Ohio.

SDH