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Cold Front Dropping South Across the Western U.S.; Watching Threat for Tornadoes and Flooding in the South

A cold front will push south across the Western U.S. into Tuesday with mountain snow and areas of gusty to high winds. An area of low pressure will form along this front on Tuesday and bring a potential for severe thunderstorms with tornadoes and excessive rainfall in the lower to mid Mississippi River Valley. To the north, heavy snow is possible in parts of the upper Midwest. Read More >

June 15, 2011 Wake Low Over Southern Lake Michigan


Article Author: David L. Beachler Senior Forecaster WFO Chicago

During the early morning of June 15th 2011, a Mesoscale Complex of Thunderstorms (MCS) developed across Eastern Iowa/Northeast Missouri/Western Illinois. This MCS continued to drift east before daybreak and began to decay across Eastern Illinois. Associated with this MCS was a line of showers and thunderstorms that pushed across Northern Illinois. The Infrared satellite imagery detecting cloud temperatures, noted steady warming within the northern periphery of the MCS over Northeast Illinois (Fig. 1a and 1b).

Infrared Satellite Imagery 15Jun2011 315AM CDT
Figure 1a:  Infrared Satellite Image 0815Z (315AM CDT)


Infrared Satellite Imagery 15Jun2011 545AM CDT
Figure 1b: Same as Fig 1a. except 1045Z (545AM CDT)


Subsequently as this warming of the clouds was occurring, evaporative cooling was unable to balance the environment due to downward motion (subsidence) in the wind field. The result of this process created what is known as a wake low to form, where strong winds were noted over far Northeast Illinois.

Strong winds developed on a small scale. This is also known as the mesoscale (5-20km range or the size of a few counties) During this particular wake low event, high winds lasted for several hours downing trees across far Northeast Illinois. (Table 1).

Definition – wake low: A surface low pressure area to the rear of a squall line.  Source: American Meteorological Society AMS


WSR-88D KLOT Wake Low Radar Reflectivity
Figure 2:WSR-88D KLOT Base Reflectivity and Marine Observations


 Air Pressure Change 15Jun2011 Winthrop Harbor IL
Figure 3:  Atmospheric Pressure Chart Winthrop Harbor IL WHRI2


 Air Pressure 15Jun2011 Kenosha WI
Figure 4: Same as Figure 3 (above) except for Kenosha WI KNSW3


Wind Gust 15Jun2011 Winthrop Harbor IL
Figure 5: Wind Gust Chart Winthrop Harbor IL WHRI2


Wind Gust 15Jun2011 Kenosha WI
Figure 6: Same as Fig 5 (above) except for Kenosha WI KNSW3


15Jun2011 Druce Lake IL
Figure 7: Air Pressure Change Druce Lake IL


15Jun2011 Cary IL
Figure 8: Same as Fig. 7 except for Cary IL


15Jun2011 Gurnee IL
Figure 9: Same as Fig. 7 & 8 except for Gurnee IL


15Jun2011 Waukegan IL
Figure 10: Same as Fig. 7,8, & 9 except for Waukegan IL


Table 1: 15Jun2011 Wake Low Wind Reports
600 AM CDT Kildeer, IL (LAKE COUNTY) Large Tree Down
 700 AM CDT Beach Park, IL (LAKE COUNTY) Wind Gust: 55 MPH
 720 AM CDT Libertyville, IL (LAKE COUNTY) Wind Gust: 54 MPH
 735 AM CDT Chicago Crib (CHII2) Wind Gust: 48 MPH
800 AM CDT Waukegan, IL (LAKE COUNTY)

Wind Gust: 45 MPH