Drenching downpours, possible severe storms all elements of Tuesday and Tuesday night’s warm, muggy weather regime



An active “ring of fire” pattern is back in place and expected to last through Tuesday night before giving way to cooler, less humid, more comfortable weather later this week.



A similar pattern helped generate the powerful and damaging derecho —the name given to fast-moving, bow-shaped lines of thunderstorms — which raced from Nebraska eastward across Iowa and northern Illinois into the Chicago area two Mondays ago on June 24. It resulted in storm damage, including downed trees and powerlines, and was followed in the four days which ensued with three additional bands of storms, each responsible for their own swaths of high winds and damage.




Clusters of thunderstorms capable of generating downpours and high winds, similar to those observed two weeks ago, rotate around masses of blazingly hot air, like the one to produce 90 and 100-degree temperatures in the Plains in coming days. This occurs because powerful jet stream winds blow around the periphery of these hot air pools and help drive storm cluster development and movement.




Monday’s Amazon River Valley-level 75-degree dew point makes this the most humid air mass to reach Chicago in over a year




But upper winds are only one component of the atmospheric set-up which leads to outbreaks of severe weather. Usually present is a large quantity of moisture in the air beneath these jet streams. This moisture serves as the “fuel” for thunderstorm development.




Dew points here in Chicago Monday evening reached the mid to upper 70s, a testament to the presence of copious amounts of moisture in the air here—moisture which drove Monday’s thunderstorms.



With more than 2″ of evaporated moisture in the air, downpours capable of producing flooding are a threat



With 2” evaporated water values in the air predicted to hover over this area into Tuesday night, the potential for vigorous and heavy rain-generating thunderstorms affecting at least portions of the Chicago area is to remain elevated.




The warm, sultry summer-like pattern in place since late last week has sent Lake Michigan water temps to seasonal highs




Water temperatures on Chicago’s shoreline reached 71-degrees Monday and 72-degrees at nearby Indiana Dunes State Park. These marked new highs for 2013 and are yet another by-product of the area’s sudden warmth.





City enters the period of year historically the warmest; normal daily high hits annual peak of 85




You know you’ve reached the year’s warmest period when Chicago’s “normal” high hits 85-degrees—as it does for the first time in 2013  Tuesday. “Normal” Chicago highs will  continue at 85 for the next week then begin a slow seasonal slide.




Far more comfortable temps and humidities on the way later this week for the Taste of Chicago; Mackinac Race to kick off in light Saturday wind regime




For the million or more visitors likely to head to the annual Taste of Chicago later this week, more comfortable weather is on the way.  Daytime highs fall back to the mid and upper 70s Thursday and Friday—but even more importantly, dew points, which offer a measure of atmospheric moisture, are to begin falling after Wednesday morning and are predicted settle into the 50s Thursday and Friday—incredibly comfortable territory in terms of atmospheric moisture. The pullback won’t be permanent, but should span 3 days. Temps ease higher over the coming weekend.




Longer range model forecasts indicate large dome of the year’s hottest air to develop over a huge area of the Lower 48; hinting at temps growing hotter next week




Longer range model forecasts project the development of a huge dome of hot air again next week. But this time Chicago is to sit in the heart of this hot air pool. The  evolving pattern has a hot “look” to it. So developments in that time frame are being monitored closely.




A factor which may play into the development of hot weather here could be Tropical Storm Chantal which over the next 5 days is to move toward the Bahamas and the Southeast U.S.




Air vented out the top of tropical systems often migrates hundreds of miles from these storms, then sinks.  It’s a process which can lead to compressional warming, potentially  capable of enhancing hot air development here in the nation’s Heartland.