Midwest Weekly Highlights - March 1-7, 2011

---

The Tail End of Winter

The taste of spring weather the last week of February gave way to a return to winter-like conditions the first week of March. Temperatures were near to below normal across most of the region, and snow returned to the upper Midwest. Heavy rain associated with a strong and slow-moving storm system brought heavy rain to the eastern portions of the Midwest causing widespread flooding.

Temperatures were much below normal across the northwestern third of the region, ranging from 16°F below normal in western Minnesota to near normal in eastern Iowa (Figure 1). Much of the central Midwest was near normal this week, with temperatures dropping of to 4°F below normal in lower Michigan and eastern Ohio. The swath of near normal temperatures in the central Midwest was largely due to two days of warmer weather occurring ahead of the midweek storm. There were only a handful of temperature records this week, mostly in Minnesota.

Precipitation was normal to much above normal from central Missouri to the southern half of lower Michgian and eastward (Figure 2). The western half of the region was much drier than normal, with most areas less than 50 percent of normal. Little precipitation was recorded in southwestern Iowa. This was actually good news for the northern Midwest, where there is still one to two feet of snow on the ground (Figure 3) and where the potential for spring flooding is high. Snowfall this week occurred across Minnesota, Wisconsin, and Michigan, with some light snow and flurries across the central Midwest in the wake of the midweek storm (Figure 4).

Flooding Rains

Precipitation began developing ahead of a low pressure system lifting out of the Southern Plains on March 4th (Figure 5). The precipitation began as freezing rain in portions of Illinois, Wisconsin, and Michigan during the morning rush hour , later changing to rain as warm air surged northward. The icy conditions resulted in numerous traffic accidents causing a number of injuries, and two deaths in Michigan. Showers and thunderstorms developed in the warm air to the south of the system, and tornado and severe thunderstorm watches were issued for parts of Missouri and Illinois. No tornadoes were reported, but there were several reports of severe hail and high wind in Missouri (Figure 6), including a 78 mph thunderstorm wind gust near Portland, MO (Montgomery County). The heaviest rain with this system occurred in southern Indiana and Ohio, where two to three inches of rain fell in a 24 hour period (Figure 7). This did not help the already high water situation in Ohio and Indiana, and at the end of the week many of the rivers and streams in Ohio and Indiana were in flood (Figure 8).

-SDH-