Expanding dome of heat to send Chicago temperatures into triple-digits for the first time since 2005—heating which could provoke gusty thunderstorm development

The brutally hot air mass responsible for hundreds of record high temperatures over the Plains in recent days and for the “heat” and “excessive heat” advisories spanning 23 states Thursday, makes its move into the Chicago area. It brings with it the metro area’s hottest June temperature in 24 years and the city’s  first official triple-digit reading in 7 years. Surging humidities are to combine with the heat to generate dangerous 105 to 112-degrees heat indices.


Only the arrival of a lake breeze at shoreline locations and on area beaches later Thursday is to moderate intense heat, lowering beach temperatures to the upper 80s to near 90.


Triple-digit temperatures rare in June; just 9 of the past 84 years have produced them 


Temperatures at or above 100-degrees are rare here in June. There have been 86 recorded between May and September at Midway Airport since weather observations began there in 1928. But only 19 of them—just 22 percent—have occurred in June and those have been scattered across just nine years.


The most recent June 100-degree reading here took place in Chicago 24 years ago during the desperately hot, dry summer of 1988.

Each of the nine previous Junes with 100+ temps finished with huge 90+-degree tallies


The nine years in which 100-degree temperatures occurred in June share an important trait—each wound up with huge tallies of 90-degree and hotter temperatures. While the long-term average number of 90s is 17 at O’Hare and 23 at Midway, each of the nine years with a 100 in June produced an average closer to 39 such days—and many of the years ended up with more the 40.


The city’s most prolific 90-degree-producing year was 1988, which ended up generating 47 daytime 90s and seven 100+degree temperatures!


Illinois EPA declares Air Pollution Action Day as ozone levels surge


Ozone levels have been increasing in recent days, a development which didn’t pass unnoticed at the Illinois EPA. The agency has issued an Air Pollution Action Day declaration for Thursday.


Nation’s Heartland sizzled Thursday; 8 states register new records; 15 topped 100-degrees


The expanding dome of hot air, which threatens to tie Chicago’s 41 year old record for June 28 of 101-degrees, produced a flurry of new temperature records Wednesday across eight states. Readings  surged above 100-degrees in 15 states.


Wetter pattern taking shape in coming days/weeks?


Several important changes are underway in the weather pattern across North America which could boost Midwest rainfall. While far too early to see what effect the evolving pattern may have on the region’s drought, it is interesting to see computer projections which place Chicago in an “above normal” rainfall regime in the days and weeks ahead.


The pattern changes are occurring simultaneously with the onset of the Southwest Monsoon, responsible for thunderstorm development Wednesday over the Rockies. Also at work is a southward-sinking jet stream, expected to lay out from Iowa to Wisconsin, Illinois and Indiana. Those high altitude winds and the sporadic, rain-generating impulses they carry, will parallel a corridor saturated with airborne moisture amounting to 2″ or more—of water—more than enough to produce occasional clusters of east-bound thunderstorms capable of downpours and gusty winds from time to time in the days ahead. It’s possible some of these storms may grow severe.

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