FIRST–THE WEATHER HEADLINES

–Very spotty showers have popped this afternoon well west of Chicago in isolated sections of Kendall and Grundy–as well as McHenry county.  We’ve noted a few radar returns in a spot or two of northwest Indiana—and in a few other locations of the Greater Chicago area. This will fade away after the sunsets

–It’s dry here–we’ve had only 14% our normal rain–just 0.44″ at O’Hare–since July 26—making the period from July 26 through Aug 17 the driest here in 39 years (1983)

–We finish the work week with NO RAIN Thursday and only a slight chance of an isolated shower Friday

–It’s the weekend which finds moderate rain and thunderstorm chances on the horizon and any showers and thunderstorms are likely to become most numerous in the warmer parts of the day. Where these thunderstorms occur, there will be enough moisture to produce local downpours. It’s just that the area impacted will be on the order of 55% of the Chicago area both Saturday and Sunday. We have the big AIR AND WATER SHOW on tap this weekend, so we’ll be monitoring developments as we move closer to the weekend and fine-tuning rain projections. But at the moment, averaging across 19 model rainfall projections, we come up with 0.41″–though the spread in predicted totals ranges widely (which you’d expect with a summer thunderstorm pattern) from as little as 0.1″ to as much as 0.9″. And with the potential for thunderstorms in the forecast, I’m not sure these numbers capture the actual range of values since thunderstorms generate huge variations in how much rain actually falls

–The reason for the weekend thunderstorm threat is a pool of cold, unstable air is to settle southeastward from the Plains and Upper Midwest into the airspace in and around Chicago. Warm air becomes buoyant and rises into this cool air. That creates the environment in which thunderstorms blossom.

–NO huge temp changes are in the offing based on modeling at the moment. Friday’s predicted 87-deg high would be the warmest daytime temp here in 3 weeks.

–Predicted weekly temp averages remain similar to those calculated yesterday:  72.6-deg this week, a reading 1.4-deg below normal, a veritable statistical “wash” compared to normal readings for the period.  And next week’s predicted 74.7 -deg average temp would be a modest 1.8-deg ABOVE NORMAL.

–If there are 90s in our future, something bound to happen again before this warm season comes to an end months from now, THEY’RE NOT SHOWING UP YET. But we’ll keeping our eyes on future trends

NOW MY LATEST CHICAGO METRO FORECAST

TONIGHT: Clouds scatter, a bit cool for the season. Low 59–but closer to 50 in the coolest locations away from the lake and the city. (Normal low is 66).

THURSDAY: Sunshine with some mixed fair-weather clouds, a bit warmer in the afternoon but with humidities remaining low and comfortable. Light easterly lake breezes will shave several degrees off beach temps in the afternoon. High 84–but mid to upper 70s lakeshore.

THURSDAY NIGHT: Partly cloudy, seasonable temps. Low 64–upper 50s inland.

FRIDAY: Sunshine and mixed clouds, warmer. Slight chance of an isolated afternoon shower. High 87.

SATURDAY AND SUNDAY: More clouds than on recent days, moderately higher humidities–and warm! Scattered showers and thunderstorms develop with rain-free hours between. Most numerous thunderstorm development is likely in the warmer hours of each day, though morning showers, especially Sunday, can’t be completely ruled out. Rain coverage may include 50 to 60% of the area each day.  High Saturday 84. Sunday’s high around 80–with modestly lower temps on area beaches.

MONDAY: A good deal of cloudiness, remaining moderately humid. Several scattered mainly afternoon and evening showers or t-storms–though, again, morning showers can’t be completely ruled out. High 79.

TUESDAY and WEDNESDAY:  Generous sunshine mixed with typical cottony summertime fair weather clouds. Temps remain warm, humidities a bit lower than early in the week. High Tuesday 81; Wednesday’s high 83–but day to day easterly lake winds bring temps down a few degrees on area beaches.