Midwest Weekly Highlights - April 1-9, 2007

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Winter's Encore Performance

Warm weather persisted a few days into the month of April in the southeastern half of the region, but then winter decided to make an encore appearance. A polar air mass spilled south through the Midwest, producing temperatures well below normal. In addition, strong and persistent northwesterly winds cranked up the lake-effect snow machine, burying much of the upper Midwest in snow after most snow from the winter had disappeared.

Temperatures the first nine days of April ranged from 4°F below normal in Ohio and much of Kentucky to as much as 18°F below normal in western Minnesota (Figure 1). The extent and persistence of the cold was impressive, considering that through the first three days of April temperatures in the eastern Midwest were averaging 14°F to 16°F above normal (Figure 2) and this trend was totally reversed in the next six days.

Precipitation was highly variable across the southern half of the Midwest, ranging from almost nothing in southwestern Missouri to near normal precipitation from southern Illinois through southern Indiana (Figure 3). Precipitation across Minnesota, Wisconsin, and Michigan was much above normal, with a majority of the precipitation falling as snow (Figure 4). While most residents could have done without the return to winter weather, the heavy precipitation helped make a dent in the drought conditions that persisted across the region since last summer. The latest U.S. Drought Monitor depicted a shrinkage in the area in Extreme Drought in northern Minnesota (Figure 5). In other parts of the Midwest, flooding was still a concern. Flooding occurred on a number of rivers in Minnesota and Wisconsin, including the Minnesota River and the Rock River in Wisconsin. Flood warnings contnued along the Mississippi River in Iowa and Illinois, and along the lower Illinois River. In Indiana the Wabash and White Rivers remained at or near flood stage.

 

A Wild Start

As April began a strong low pressure system was centered over southern Minnesota (Figure 6), and the first surge of colder air was entering the northern Midwest. This system moved quickly to the east, and by the morning of April 3 another strong low was winding up over southern Iowa (Figure 7). The circulation around this low brought much warmer air into the southern half of the region, and a few record high temperatures were set in Missouri and Ohio. This was a potent weather system, with wind profiles in the warm air favorable for severe weather. North of the low pressure center, the much colder air supported snow in the northern Midwest. By mid-morning on April 3 winter storm watches, warnings, and advisories were in effect for the upper Midwest, while severe thunderstorm watches stretched from the Kansas-Missouri border east to central Indiana (Figure 8). As the day progressed severe thunderstorms were numerous reports of large hail, including 4.25 inch (softball) hail in Hart County, Kentucky, 2.75 inch hail in Missouri and Indiana, and 1.75 inch hail in Missouri, Illinois, and Indiana. By afternoon the severe thunderstorms transitioned from "hailers" to storms with damaging winds and some tornadoes. A tornado touched down in southern Indiana, and several EF1 tornadoes caused damage in Kentucky during the late afternoon and evening. Heavy rain fell across southern Wisconsin and Michigan (Figure 9), with daily maximum rainfall records set at Milwaukee and Madison, WI; and at Grand Rapids and Muskegon, MI.

 

Winter Cranks Up - Again !

The low pressure system continued to intensify as it moved northeast. Blizzard warnings were issued for the Michigan Upper Peninsula by late afternoon on April 3 and were continued into April 4, including northern lower Michigan (Figure 10). By the morning of April 4 the low pressure center was located over the northern shore of Lake Huron (Figure 11), and the deepening low was producing winds of 30 to 40 mph with gusts 50 to 60 mph over the northern Midwest. High wind warnings were issued for eastern Wisconsin south through northern Illinois and Indiana. In Chicago, winds damaged a roof panel on U.S. Cellular Field, home of the White Sox. Across the Michigan UP, the high winds whipped around heavy snow producing whiteout conditions.

To say this was an impressive storm for the upper Midwest is an understatement. Strong northwesterly winds persisted for five days across the Midwest, maintaining a flow of cold polar air into the nation's midsection. The lake effect snow machine was in overdrive across the Michigan UP, northern Wisconsin, lower Michigan, and late in the period, Ohio. There was little snow remaining on the ground on April 1 across the Midwest except for a small part of the Arrowhead of Minnesota and the northeast UP of Michigan (Figure 12) because of the unusually warm weather during the latter half of March. However, by April 9, more than three feet of snow covered the northern UP of Michigan, and snow cover was evident from the northern half of Minnesota across all of lower Michigan and northern Ohio (Figure 13).

Snowfall amounts from this storm in excess of three feet were common across the Upper Peninsula (Figure 14), and in places the snow was 4 to 5 feet deep with drifts in excess of 8 feet. This photo of a six-foot drift in front of a house was taken near Mohawk, MI in Keeweenaw County (courtesy www.johndee.com). Painesdale, MI on the Keeweenaw Peninsula (Houghton County) reported a total of 64.5 inches of snow through 8:00 p.m. EDT on April 8. The Marquette, MI National Weather Service office received 48.5 inches of snow, and set a number of snowfall records for April (records date back to 1961). These included:

• Greatest 2-day snow accumulation in April - 31.2 inches, April 4-5,2007
• 2nd greatest 1-day snowfall - 24.0 inches, April 4, 2007
• 3rd greatest 2-day snowfall - 31.2 inches, April 4-5, 2007
• 3rd greatest 3-day snowfall - 37.9 inches, April 4-6, 2007
• 2nd greatest 4-day snowfall - 41.0 inches, April 3-6, 2007
• 2nd greatest 5-day snowfall - 48.5 inches, April 3-7, 2007
• Snowiest April on record - 48.5 inches (through April 8)
  

Record snowfall also occurred over northeastern Minnesota, where Duluth received 12.1 inches on April 6, the most for any single day in April. Silver Bay, MN (Lake County), on the northern shore of Lake Superior, received 13.3 inches, just 0.7 inches short of the state record for April 6 of 14.0 inches received in Kettle Falls (St. Louis County) on this date in 1982.

Lake effect snow also persisted over lower Michigan and in the Lake Erie snow belt in Ohio. More than 30 inches of snow accumulated in Geauga County, OH, with Chardon, OH reporting 32.6 inches and Claridon Township receiving 31.5 inches (Figure 15). The Cleveland Indians baseball team was unable to play their home opener on April 6 because of snow, and the entire four-game series against the Seattle Mariners was snowed out. Ten inches of snow covered Jacobs Field, and the grounds crew gave up trying to keep up with the snow. On April 9 the team announced that its series against the Los Angeles Angels of Anaheim scheduled to begin on April 10 was being moved to Milwaukee's Miller Park, which has a retractable roof. This is only the second time since 1961 that weather has forced a major league game to a new location.

 

A Shivering End

Much of the northern Midwest experienced an uncharacteristically white Easter (Figure 16), and the entire region shivered as a persistent northwest flow of air kept temperatures more than 20°F below normal. In fact, weather conditions across the Midwest were more winter-like than they were on Christmas 2006 (Figure 17). Reinforcing shots of cold air, accompanied by some light snow and flurries away from the lake-effect areas, swept through the Midwest the last few days of the period as upper level disturbances rotated through the major trough the dominated the eastern half of the country (Figure 18). Temperature records were set in the Midwest April 6-9, with the most records on April 7. More low temperature records would have likely fallen had clouds not covered most of the region. Freeze warnings were issued for much of the Midwest. While freezing weather is not at all unusual in early April, the warm weather of late March promoted rapid development and plants and tree buds. The prolonged freezing threatened fruit crops, in particular. A hard freeze (temperatures less than 24°F ) occurred over the entire region on April 7, with subfreezing temperatures well south of the Ohio River (Figure 19).

Temperatures began to slowly warm on April 9, with highs reaching the mid 50s in Missouri and the 40s as far north as southern Minnesota and Wisconsin. Although this was warmer than the previous several days, maximum temperatures were still 6°F to 14°F below normal (Figure 20).

Many of the temperature records set during the first nine days of April can be seen in Table 1.

 

SDH