Midwest Weekly Highlights - May 11-17, 2008
Cool Weather Maintains Hold, Rain Stays East
Much colder than weather continued through the second full week of May in the Midwest. Temperature departures below normal were greatest over the southern half of the region, where they ranged from 5°F to 7°F below normal (Figure 1). Temperatures in the northern half of the Midwest were generally 3°F to 4°F below normal, although a small area from near Green Bay, WI into northern lower Michigan was only 1°F to 2°F below normal. The significant snow on the ground finally disappeared from the northern Arrowhead of Minnesota on May 15.
Rain this week was largely confined to the southeastern half of the region (Figure 2), where it was 150 to 200 percent of normal. Rainfall was also above normal in small parts of Minnesota and northern lower Michigan. With a few exceptions, precipitation since April has been normal to 125 percent of normal across the Midwest (Figure 3), coming on the heels of a wet winter season. Frequent precipitation and the cooler weather has slowed the progress of spring planting in the Midwest, and as of May 12 all states in the region except Michigan were behind the 5-year average in planting progress, ranging from only 11 percent behind in Indiana to 50 percent behind in Missouri (Figure 4).
Winds Howl Across the Midwest
The low pressure system entering the western Midwest on May 10 rapidly intensified as it moved to northern Illinois and Indiana on the morning of May 11 (Figure 5). One to three inches of snow fell in St. Louis County, MN in the cold air behind the low. The large pressure gradient produced strong sustained winds and gusts frequently in excess of 40 mph in the western half of the region, while portions of Iowa, Missouri, and Illinois experienced wind gusts in excess of 50 mph (Figure 6). Winds gusted to 61 mph at the Macomb, IL airport, and 60 mph at Pawnee, IL and Decatur, IL. The wind gusts did result in some tree limb and structural damage, and produced scattered power outages. The storm system moved steadily east during the day, and by early afternoon the center was clearly seen over southwestern Ohio on the visible satellite image (Figure 7). Severe storms erupted ahead of the cold front associated with the low, mostly in eastern Kentucky. There were two reports of tornadoes in Kentucky, and one in Ohio. By late afternoon winds over the central Midwest had considerably subsided as the storm moved away and weakened.
Colder air spilled into the Midwest behind this system, keeping temperatures below normal. Springfield, MO set a new record low of 37°F on May 12, breaking the old record of 37°F set in 1960. Vichy-Rolla, MO reached a new record low of 36°F, shattering the old record of 40°F set in 1960.
Scattered Severe Weather, More Heavy Rain
Another cold front began pushing into western Iowa and Missouri on May 13, setting off scattered severe thunderstorms in Missouri, Iowa, and Illinois. A brief tornado touchdown was reported in Barton County, MO and 1.50 to 2.00 inch hail was reported near Morton in Tazewell County, IL. This front stalled south of the Ohio River on May 15, and a low pressure wave riding along the front produced a shield of rain from southern Missouri into northern Kentucky, then northward through central Illinois and Indiana. rainfall ranged from 1.00 inch to 2.00 inches in a band from the Missouri Ozarks east northeastward through the Ohio Valley (Figure 8).