UPDATED AT 5:05 P.M. Friday: It's now official -- Chicago's streak of above 80-degree days has ended! The temperature Friday peaked at 80 degrees -- below the 81 required to keep the string of "above 80 days" going. That finalizes the just completed "above 80 degree" string of high temperatures at 29 days. It's the longest above 80 string in 140 years of records here. The 80-degree high at O'Hare Friday is July's 2nd coolest daytime reading -- second only to 77 on July 1.
UPDATED AT 2:45 P.M. Friday: Got questions about whether there will be rain at Soldier Field for tonight's Bon Jovi concert. Looks like there could be -- some rain has already started to fall in portions of Chicagoland. Bringing something to protect yourself from the elements would be as good move -- whether you're going to Bon Jovi or the Sox game. Total rainfall projections for the next two days approximates a half-inch.
UPDATED AT 2:29 P.M. Friday: The temperature reached 80 at O'Hare during a burst of sun ahead of incoming showers this afternoon. But the day is still on tap to be the "coolest" -- though by no means truly chilly -- since July 1's 77-degree high. If the day's high stays at 80, we will have broken the string of consecutive above 80-degree (i.e. 81 or higher) which reached a record 28 days Thursday, the longest such string in 140 years of weather records here.
By Tom Skilling
An influx of clouds Friday will help produce Chicago's coolest daytime high since early July. Temperatures are predicted to struggle just to hit 80 -- and in sections of the Chicago area may fail to do so. This comes only a day after establishing the city's longest string of consecutive above 80-degree highs since weather records began 140 years ago.
The temperature downturn is temporary -- it won't last. But it comes in a July with only one sub-80 daytime high to its credit and only three days which have averaged below normal. Through Friday -- with just two days left in the month -- the average temperature of 77.9 degrees continues to make this the sixth warmest July on record since 1871. That temperature suggests air conditioner usage this month has likely run at a pace nearly three times normal.
Cloudiness, while far more extensive than on Thursday, isn't likely to completely block the sun -- nor is it likely to generate huge rains. Some sunlight is apt to filter through the clouds at times. Only a few sprinkles are expected -- and those are expected to affect only a few locations Friday if they occur at all.
An impulse due to pass across the area late Friday night into Saturday morning runs the best chance of producing higher-coverage light showers. These showers may affect as much 60 to 80 percent of the metro area beginning late Friday night -- most likely beyond midnight. Rains scatter Saturday allowing a number of rain-free hours. What will have to be monitored is the extent of any heating Saturday. Heating, given a modest degree of instability predicted by models here, could encourage air to rise and cool, possibly generating a few isolated afternoon thunderstorms. Only 20 percent of the area would be affected by such storms.
Western monsoon includes drenching t-storms across Arizona, sends mid/high level moisture into Chicago
The North American Monsoon is under way over the Western U.S. It marks the onset of the summer wet season there -- particularly in Arizona, New Mexico and the Rocky Mountain states just north. Interestingly, its onset becomes official in southern Arizona when dew points reach or exceed 54 degrees over three consecutive days. That's happened in Tucson and Phoenix -- areas hit Thursday by powerful winds in downpour-generating thunderstorms. Storm gusts in Phoenix reached 75 mph and at least one Weather Bug rain gauge there registered 3.12 inches. Other totals included 1.65 inches at Surprise, 1.22 at Peoria and 1.14 at Chandler -- all in Arizona -- and forecasters there caution the current "high grade" phase of the monsoon has several days to run. The powerful gusts produced by Thursday's storms caused roof damage at the University of Phoenix football stadium, home to the Arizona Cardinals.
The atmospheric water content over Arizona Thursday exceeded 2 inches at many locations and Phoenix recorded an almost unheard-of (by Arizona standards) peak dew point of 80-degrees. It's likely that reading ranks among the highest dew points ever recorded there.
The monsoon has a Chicago connection. High and mid-level moisture off the monsoonal storms is being carried by jet stream winds into the Midwest and contributing to the frequently cloudy skies predicted here the next few days.
Resurgent heat pushes temps well into the 80s Sunday and into the 90s Monday and Tuesday
Longer range trends remain VERY "summery" in appearance. A dome of heat, capable of generating highs close to the year's top reading of 94 degrees to date (recorded on July 23), appears to be taking shape for Monday into Tuesday. With Chicago predicted to sit beneath the nose of a pocket of especially strong jet stream winds -- a so-called "jet streak" -- broad subsidence of the air over Chicago may well subdue thunderstorm growth while producing compressional warming likely to boost daytime temperatures. This along with the predicted return of exceedingly muggy mid-70-degree dew points is making Monday look pretty steamy.
With 2 inches of evaporated water in the air Tuesday, heat in place, winds predicted to converge along an incoming cold front, and temperatures likely to fall at a steeper than usual rate with height, the stage could be set for clusters of heavy rain-producing thunderstorms Tuesday.
After a break, even hotter air could be on the way a week from this weekend if some models are correct. Especially aggressive in warming Midwest weather is the European Center's medium range forecast model. Wet soils may come into play and end up limiting some of that heating -- but, if not, the Chicago area could be in for yet another surge of humid heat beyond the coming 7 days.
