Jarring evening temp drop with a wind shift to the “NE” in Chicago as “pneumonia front” sweeps through Tuesday evening

Sunshine and cool temps follow Wednesday—spring, 2023 is the driest 33% of past 151 years here and no rain expected until Friday

Chicagoans come off a cool Mother’s Day weekend. High temps averaged 3.5 degrees below normal Saturday and Sunday—but when low temps are included, the weekend was actually finished close to normal. What made it feel so much cooler was the fact the weekend averaged more than 10 degrees cooler than the weekend which preceded it.
Tuesday is to throw some thermal curves at Chicago—warming into the low 80s in the afternoon. But, a WIND-SHIFTING PNEUMONIA FRONT—so labeled because of the jarring temp changes it produces—will sweep through the city from the north passing in the evening hours Tuesday.
Within a matter of hours, temps will crash down to 30 degrees—falling from the low 80s into the low to mid 50s. Current indications are that the front will pass the city around 6 to 7pm—earlier North Shore areas and NNE winds will sweep in gusting 25 to 30 mph along the lake.
This will introduce building waves and the onset of possible rip currents Tuesday night—something swimmers and area mariners should be aware of.
Lake water temps remain VERY CHILLY—averaging 50 degrees. So any swimming in such cold waters introduces a hypothermia risk which can sneak up on swimmers. It’s a little early in the season to be in such chilly waters for any period of time.
What follows is a cool Wednesday with cool winds off Lake Michigan—then, a slow daytime temp rebound toward 80 by Thursday.
Cooling follows this weekend into early next week. But, evidence for significant warming by the middle and end of next week continues to grow.
While this week’s temps are to come in near normal overall, temps next week, given current forecast trends, are to surge 7 degrees higher on a week long basis and nearly 4 degrees above normal. This translates to daytime average temps surging 5 to 11 degrees above normal each day from Wednesday forward and daily highs reaching into the low and mid 80s from Thursday and forward onto next week.
The area continues dry. Precipitation—since the beginning of meteorological spring on March 1st—ranks among the 33% driest springs of the past 151 years with rainfall more than 3 degrees below normal. While some showers are possible Friday, rainfalls aren’t showing signs of rebounding here significantly through the coming weekend.

IT’S DRY—THE METEOROLOGICAL SPRING 2023 SEASON (WHICH BEGAN MARCH 1) CURRENTLY RANKS AMONG THE DRIEST 33% TO DATE

Rainfall since April 1 is running 41% normal — down 3.42” at O’Hare from the period’s normal tally at the site of 5.83” — but might summer see a precipitation reversal here?

That’s the suggestion of some modeling and of the official National Weather Service summer season (i.e., June, July and August) precipitation trend forecast—but, it’s worth noting warm season precipitation projections can be dicey

Seasonal forecasts are tough and can fall short of the mark. That’s never more true than when trying to identify METEOROLOGICAL SUMMER SEASON (June, July and August) RAINFALL TRENDS. We’ve all witnessed just how varied and often localized warm season rains can be. We can literally see one area flooded while another suffers a state of drought. By the same token, the intensity of rainfall which can occur in warm season t-storms can be formidable and reverse dry patterns on occasion.
WGN meteorological colleague, Tim Joyce, presented an excellent analysis of the paltry precipitation we’ve seen here in the city to date of late.
It’s true—there have been some BIG RAINS in localized areas south of the city where more than 3” fell a weekend ago. But, the area pelted by those downpours was localized—a fairly narrow corridor. Some places recorded as much as 3.80” amid dramatic lightning displays in storms which included huge hailstones. At the same time, however, rainfall in Chicago came in a just hundredths of an inch.
Unfortunately, the dust storm responsible for the deadly traffic pile-up several weeks ago downstate near Springfield on I-55, certainly due in part to drier than normal conditions there, offered an insight into the drier than normal conditions which are far more widespread over a region impacted by recent heavy and thundery rains.
Just check out the latest 2023 Spring season analysis from the Midwestern Regional Climate Center at Purdue University. And as colleague Tim Joyce so accurately noted, the latest NWS/USDA Drought Monitor, released last Thursday, is on to the fact we’re running dry as we enter the new growing season.

SHORT TERM—THERE WILL BE SOME RAIN, BUT MODELING SUGGESTS RAINFALL IS TO REMAIN “BELOW NORMAL”

Out into the medium term (i.e. the coming two weeks), modeling offers little indication a big change in the drier than normal pattern is in the offing. To be sure there will be some rain, but current projections for the Greater Chicago area to continue with sub-par rainfall. These medium range forecasts take us into late May.
Predicted summer season precipitation trends provide some evidence of an “above normal” precipitation trend
Longer range model projections and the official forecast of the potential summer precipitation trend have been quite persistent in suggesting a potential shift to above normal precipitation for the June, June, August Meteorological summer period.
We always walk a fine line in the warm season. The atmosphere at that time of year is warm and therefore capable of carrying copious amounts of moisture. Also, t-storms, which can be prolific rain producers, roam the terrain in summer. Just how they lay out can have a profound impact not only on precipitation trends, but on the summer season’s precipitation.
It’s a simple fact that warm season precipitation falls in a far more varied manner than colder season precipitation, when rains and snows come with better developed, more widespread weather systems.
Modern seasonal forecasts are very often the product of “blends” or “averages” of the precipitation predicted by a set of models, each with its own sophisticated physics packages and means of handling the initial weather observations indicated the atmosphere’s “initial state” as the forecast cycle begins. Human forecasts bring their own expertise to the process, attempting to correct for model biases and inaccuracies. Seasonal forecasts are better than ever before, but they’re not perfect.
Linked to summer precipitation patterns are their impact on temps. T-storms are giant “atmospheric air conditioners.” The outflow of rain-cooled air from such storms can modify/reduce the impact of heat. By the same token, lack of rainfall can allow temps to “take off.” It was no accident that our hottest summer, in terms of 90 and 100-degree days—the summer of 1988—was desperately dry. There were fewer t-storms than typical and Chicago ended up with 47 days at or above 90 and 7 days with temps at or above 100 degrees—the most 90s and 100s of any summer on the books here. The impact on crops was devastating.
So there’s much to monitor here with just 16 days left in May, the 2023 meteorological spring season and another growing season getting underway.