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**
TIME	LOCATION	OBSERVATION
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