Midwest Weekly Highlights - June 10-16, 2006

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Scattered Rain, Below Normal Temperatures

Most of the Midwest experienced below normal temperatures this week as the region remained under the influence of  upper level northwest flow.   Temperatures were 6°F to 7°F below normal  across much of Ohio, with temperatures from 4°F to 6°F below normal northwest through Illinois into northeast Iowa (Figure 1).  Above normal temperatures were found only southwestern Missouri and extreme northwestern Minnesota.  

The rainfall pattern for the week revealed the southern extent of the upper level trough where it marked the boundary between cool, drier air to the north and warm, humid air to the south.  Rainfall was near to above normal in a band from southwestern Minnesota across northern Illinois into eastern Kentucky (Figure 2).  Rainfall was also well above normal over northeastern Missouri.  Outside of these area. rainfall amounts fell of drastically, with very dry conditions across lower Michigan, northeastern Ohio, and southwestern Missouri. Total rainfall for the first 16 days of June was well below normal across much of the region (Figure 3), with only an area from northeastern Missouri into the Ohio Valley receiving normal rainfall. The June 13th edition of the U.S. Drought Monitor shows moderate drought in wester-central Missouri southern Iowa, and a very small portion of western Illinois (Figure 4).  Abnormally dry conditions appeared this week in northeastern Minnesota/northwestern Wisconsin.

An Unseasonably Cool Start

A strong ridge of high pressure dropped south out of Canada and into the Midwest on June 10 and resulted in a chilly start to the week.  An upper level disturbance moving southeast through the region produced an area of clouds and showers. The clouds and rain contributed to the cool weather, and the result was a number of locations setting new record low maximum temperatures on June 10, and some record lows on June 11 and 12. Minnesota reported the lowest temperature in the 48 contiguous states on June 10 (25°F at Embarrass), June 11 (26°F at Embarrass), and June 12 (32°F at Grand Marais).  While temperature struggled to reach 60°F in the areas of the northern Midwest, the far southern portions of the region were into the low to mid 90s (Figure 5).

 
June 10 - Record Low Maximum

Station	Value (°F)	Old Record/Year
Decorah, IA	57	60/1903
Dubuque, IA	59	63/1883
Charles City, IA	55	58/1923
Mason City, IA	55	59/1908
Oelwein, IA	59	66/1955
Waterloo, IA	58	60/1923
Lincoln, IL	65	66/1955
Moline, IL	59	63/1923
Peoria, IL	61	65/1955
Austin, MN	54	62/1995
Rochester, MN	59	63/1995

June 11 - Record Low Minimum

Station	Value(°F)	Old Record/Year
Merrill, WI	32	34/1980

June 12 - Record Low Minimum

Station	Value(°F)	Old Record/Year
Youngstown, OH	42	42/1979

Storms Produce Flooding Rains

The frontal boundary separating the two air masses was the focus for severe thunderstorms on June 10 in Missouri. The storms produced flooding rains, wind damage, and at least one tornado in central Missouri. Radar estimated and surface measurements showed rainfall of three to six inches, which closed many roads in north-central and east-central Missouri, including the counties of Monroe, Shelby, Audrain, Boone, Callaway, Montgomery, and Warren. The cold front continued to push southward, setting off thunderstorms ahead of it in Kentucky on June 11. By June 13 the cold front had advanced to the Gulf of Mexico and high pressure brought pleasant weather to the region.

 
Summer Returns

As the high pressure system moved east on June 14-15 winds turned southerly across the western half of the region, drawing warmer and more humid air back into the Midwest. A low pressure system diving into the Midwest from the northern Rockies triggered heavy thunderstorms across southwestern Minnesota and western Iowa from June 13 to June 15.  On June 13 the public reported 1.00 inch hail covering the ground in Porter, MN (Yellow Medicine County).  By the morning of June 14 radar indicated rainfall of two to four inches had fallen over southwestern Minnesota and four to six inches over small areas of northwestern Iowa (Figure 6), causing some flash flooding.  Sioux City, IA reported 2.71 inches of rain and Cherokee, IA reported 2.66 inches of rain.  However, the heavier rain was very localized and most locations received only 0.30 to 0.75 inch of rain in general.  

By June 16 locations in the Midwest which had experienced record or near record cold the first two days of the period were recording temperatures 30°F to 35°F higher by the end of the period as the strong southerly winds pulled air northward from the Gulf of Mexico (Figure 7).  High temperatures on June 16 reached the low and mid 90s as far north as northwestern Wisconsin (Figure 8).

SDH