Heat's grip on Chicago's weather tightening, it's the area's hottest spell since four consecutive 90s in August last summer

This year’s handful of 90s to date here in Chicago-places it among the 10 least prolific 90+-degree-producing summers of the past 142 years through mid July. But the area’s weather is well on its way toward change. Coming days will see a proliferation of 90-degree and higher temps here, readings all but absent much of the warm season to date.

 

Not only did June 2013 generate a modest 0.3-degree monthly temp deficit, Chicago’s July temperature departure is running close to a degree below normal. But not only are hotter days coming, model forecasts out to two weeks indicate the current hot spell won’t be the last! Longer range computer projections, which accurately identified the current hot spell well over a week ago, hint heat may build back into the area next week after a weekend hiatus.

 

The developing hot spell has the Chicago area moving toward its longest string of consecutive 90-degree and higher daytime temperatures in more than 11 months-since a four-day 90-degree streak which ran from August 1st through 4th last summer. That 4-day streak was dwarfed by a 7-day 90+ degree spell which was underway on this date a year ago. That one ended up producing the following string of highs from July 12th through 18th: 91, 93, 90, 95, 97, 99 and 94-degrees.

 

Less numerous, more widely scattered afternoon thunderstorms Tuesday to allow temps to move higher

 

The combination of the rain-induced outflows from towering thunderstorms late Monday morning and afternoon and the day’s “cooler” easterly lake breezes, moderated (i.e., eased) Monday’s warming a bit.

 

Highs hit 89 at O’Hare while reaching 92 at Midway-THAT site’s fourth 90-degree temp of the year to date-while peak lakeshore readings only made it to 84.

 

A modest decrease in the areal coverage of Tuesday’s humidity-driven afternoon showers and thunderstorms is to allow temps to move a few degrees higher than on Monday-with even higher readings ahead Wednesday, Thursday and possibly Friday.

 

The current warm spell’s final day of easterly lake breezes to only modestly dial back beach temperatures, southwest winds in coming days to propel heat right up to the lakeshore

 

The change most likely to influence the level of warming here the remainder of the work week revolves around the predicted arrival of southwesterly winds in coming days. These stronger west/southwest winds are likely to force warmth all the way to the lakeshore and beyond, eliminating any lake cooling there Wednesday, Thursday and Friday.

 

Week’s most intense heat to send heat indices toward dangerous levels Wednesday, Thursday and possibly Friday afternoon.

 

Heat indices, the product of a formula which melds temperature and dew point readings into a single measurement or “apparent temperature”, attempts to describe just how warm the atmosphere is likely to “feel” given the moisture levels which are present. Current forecasts put peak heat indices near 105-degrees Wednesday, Thursday and potentially Friday as well-a level considered potentially dangerous.

 

Shoreline Lake Michigan temperatures reach a new 2013 high, warmest water temperatures have occurred in August the past 6 years

 

Chicago’s lakeshore water temperature Monday surged to a new season high of 77-degrees. That’s 3-degrees lower than the same period a year ago, but it’s also this region’s highest lake water temp of 2013.

 

An in-house analysis of Chicago’s shoreline water temperatures the past 6 years indicates peak readings are likely still weeks away. Since 2007, the warmest shoreline readings here has occurred on or about August 6.

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