Cool air has been whittling away at Chicago's average meteorological summer temperature in the past week. It's been a slow process likely to accelerate again later this week as another punch of cool Canadian air rides strong northerly winds into Chicago after a vigorous cold front passes Thursday afternoon.
1988 pulls ahead of 2012 count of 90-degree and higher temps; meteorological summer only 0.2-degrees ahead of Summer 1921 to-date
To-date for the 2012 season which began June 1, Chicago's 76.8-degrees average temperature---while well above normal---is only 0.2-degrees away from ceding its role as the city's "all time warmest" to the summer 1921.
This summer's 40 days of 90-degree and higher temperatures has been surpassed by the 1988 tally of 43 such readings to-date.
"Greenland blocking pattern"---known to drive waves of cool weather into the Midwest and Eastern U.S.---to remain in place into next week; if true, model predictions of warming then are overdone
The reappearance of Greenland blocking is playing a major role in cooling Chicago and the Midwest. The past six days have averaged 5.2-degrees below normal. And, we've not seen the last of the cool air it's driving across a good swath of the nation's mid-section and East.
Global model forecasts keep the warm dome of air in place across northern Canada and Greenland into next week. This would seem to contradict predictions of extended warming next week. It's a situation which will be monitored---but it's clear much cooler air is on the way this weekend.
Strong, possibly severe thunderstorms, to erupt here as strong cold front knifes into the area Thursday
The arrival of a strong cold front Thursday afternoon argues for waves of active thunderstorms here. These storms may be accompanied by powerful wind gusts and downpours in parts of the area.
The unstable cool air mass which takes over in the wake of these thunderstorms Friday and through the weekend may provoke widely scattered afternoon and evening showers---even several isolated t-storms in the warmer parts of the day.
While Chicago cools, the West bakes.
Extreme heat is prompting advisories in the West. Phoenix hit a triple-digit record high Tuesday for a third day, and hasn't seen a temperature below 90-degree in 8 days.