Widespread damage and 30 total tornadoes across northern IL & northern IN within a derecho

June 30, 2014

Fast Facts	Storm Reports	Damage Surveys
Environment	Rainfall	Other Links

Fast Facts

Widespread wind damage, some of it significant, occurred across northern Illinois and northwest Indiana with a strong second round of storms between 8:30 pm and 11 pm.

There were 29 total tornadoes across all of northern Illinois and all of northern Indiana over an area spanning three NWS forecast areas.

18 total tornadoes were confirmed within the NWS Chicago County Warning Area, many embedded within severe winds.

There were 11 total tornadoes across northern Illinois, all of which were in the NWS Chicago County Warning Area including one that went into Indiana.

There were 17 total tornadoes across northern Indiana, six of which were in the NWS Chicago County Warning Area, including one that moved into Indiana from Illinois.

24-hour rainfall amounts were highest in parts of Cook, DuPage, and Kane Counties and Lake County in Indiana, with 2 to 3". There were isolated higher amounts, including 4.12" in Winnetka and 3.16" in Gibson City.

Storm Reports

Storm Reports

June 2014 Storm Data Publication (List of storm reports and tornadoes)

Damage Surveys

...UPDATED SUMMARY OF JUNE 30 2014 TORNADOES...

THE FOLLOWING IS A SUMMARY OF THE TORNADOES THAT ARE BELIEVED 
TO HAVE OCCURRED IN THE NWS CHICAGO AREA OF RESPONSIBILITY DURING 
THE SIGNIFICANT SEVERE WEATHER EVENT OF 30 JUNE 2014. IN 
TOTAL...18 TORNADOES WERE DOCUMENTED...SEVENTEEN OF WHICH WERE 
EF-1 AND ONE THAT WAS EF-0 IN INTENSITY. DETAILS FROM ELEVEN OF 
THESE PATHS WERE PREVIOUSLY SHARED.  SEVEN MORE PATHS WERE 
DETERMINED AFTER AN ADDITIONAL GROUND SURVEY CONDUCTED LATER IN 
JULY OVER AN AREA NOT REACHED BY THE INITIAL SURVEYS.

THE PATHS IN THIS CONCENTRATED OUTBREAK OF SQUALL-LINE TORNADOES 
WERE CORRELATED WITH RADAR SIGNATURES AND SPOTTER OR PUBLIC 
REPORTS...AS WELL AS AERIAL SURVEY RESULTS WHERE POSSIBLE.  
GUIDANCE ALSO WAS DRAWN BOTH FROM PUBLISHED RESEARCH PERTAINING 
TO SIMILAR EVENTS AND FROM COLLABORATIONS WITH DAMAGE SURVEY EXPERTS.

EVEN WITH ALL OF THESE TORNADOES...IT IS IMPORTANT TO NOTE THAT 
WIDESPREAD IMPACTS FROM THE JUNE 30TH STORMS ALSO RESULTED FROM 
SEVERE STRAIGHT-LINE WINDS...AT TIMES TO 100 MPH OR HIGHER. THIS 
WAS THE CASE NOT ONLY IN THE NWS CHICAGO COUNTY WARNING AREA BUT 
MUCH OF THE REGION IMPACTED BY THESE STORMS. MANY OF THE TORNADOES 
IN THE NWS CHICAGO COUNTY WARNING AREA WERE EMBEDDED WITHIN THESE 
SIGNIFICANT WINDS.

Detailed Summary of Damage Survey Results & Radar

Environment

June 30th 6:30 pm - 11:30 pm NWS Chicago 0.5° Reflectivity Loop

Click for high resolution loop

The severe weather event of June 30th, 2014 was quite unique. Two especially standout characteristics were that the event 1.) encompassed two separate derecho episodes in the Midwest, with one literally forming on the heels of its predecessor and 2) the second derecho brought over two dozen embedded tornadoes to northern Illinois and northern Indiana.

A complex of storms, even one not as potent as a derecho, often alters the environment for hours after in such a way that it is no longer conducive for thunderstorm redevelopment or intensification. This is because rain-cooled air limits convective lift, the low-level wind field is quite disrupted, and broad descent is often occurring in the atmospheric mid-levels (the opposite storms need). On June 30th, the first complex of storms had a minimal to nil effect on the environment. In fact, it may have even slightly helped the environment for embedded tornadoes in Kankakee County and into northwest Indiana, as it placed an east-to-west boundary over that region. The southern portion of the first derecho began weakening in intensity as it moved across northeast Illinois into northwest Indiana, with the cooling of the atmosphere being very shallow. Thus when a well-organized complex of storms moved into that environment, the downdrafts (winds) could easily punch their way through that layer.