It appears, beyond brief warming—first in the south suburbs Wednesday—then over the city and remainder of the Chicago area Wednesday night and Thursday—that we’re entering a cooler than normal period overall in the next 2 weeks.
What’s more, if there’s another 4-day run of 80s to come in the coming two weeks, it’s not showing up yet on the constellation of models we examine as guides to our forecast preparation each day. It seems safe to say—at least this point—that we NOT likely to see another 4-day run of 80s such as the one which occurred last Wed-Thu-Fri and Sat—any time soon. It will happen as we get deeper into the warm season—just not in the foreseeable future.
HERE’S MORE ON WHAT I’VE FOUND IN APRILS (Beyond April 18th) IN THE PAST HALF CENTURY IN CHICAGO
THE SATURDAY TO MONDAY 44° TEMP DROP, from a July-like 83° high Saturday to Monday’s blustery and chilly 39° high with a dusting of morning snow in a number of locations across Chicago, ISN’T RARE. Not every years sees anything quite as dramatic-—but it sure happens.
It’s not surprising big temperature swings and April go together here:
Chicago’s April Temps Beyond April 18
I poured over April temps beyond the 18th from 1973 through last year and here’s how frequently the following high temps showed up in the final weeks of April over that 50 year period:
Highs hitting 80° or higher on at least one day: In 22 of 50 Aprils beyond the 18th–that’s 44% of the Aprils examined since 1973
Highs topping 70° beyond April 18th: in 46 of 50 years—suggesting strong odds we’ll see such a temp before the month ends—warmth like that isn’t yet ready to stick around.
ON THE OTHER HAND—IT CAN GET CHILLY HERE IN LATE APRIL:
35 of 50 Aprils (beyond the 18th) since 1973—that’s 66% of them—had 1 or more days with highs which didn’t make it out of the 50s.
And, I looked at the warmest high temp and the coolest high temp beyond April 18th in the 50s years going back to 1973, the average spread between was 31° in any given year. That means—NO SURPRISE HERE: BIG APRIL TEMP SWINGS ARE NO STRANGER TO CHICAGO.
Of all the Aprils since 1973–the highest official daytime temp I found in Chicago since 1973 was 91 degrees in 1980 and the chilliest post April 18th high temp which is on the books here was 40-deg in 2013. Highs of 41 deg occurred beyond April 18th in 2022, 1993 and 1984.
THE MESSAGE IN ALL THIS—Warmth has occurred in late April—it just doesn’t stick around. We have to warm the lake up for the warmth to occur—and then stick around. So keep the full spring wardrobe close at hand!
A SPECTACULAR GOES EAST WEATHER SATELLITE ANIMATION OUR MOST RECENT LARGE SCALE SPRING STORM SYSTEM THIS PAST SUNDAY INTO MONDAY
WATCH THE STORM RESPONSIBLE FOR BRINGING AN END TO OUR 80° WARMTH–but also for dusting sections of the Chicago area with Monday morning snow while burying sections of western Wisconsin under as much as 21″ of snow Sunday into Monday morning.
The satellite animation is courtesy of the folks at CIRA/RAMBB.
GOES EAST satellite image of the early week storm over the St. Lawrence Valley to Chicago’s east—and of THE NEW SPRING STORM crossing the Rockies:
CLICK ON SLIDESHOW TO VIEW THE EVOLVING PATTERN:
Check out this weather satellite view of the snow covered ground in western Wisconsin and eastern Minnesota Tuesday. Parts of western Wisconsin picked up as much as a 21″ of snow only days past record-breaking 90-deg heat last week. 
The web isobars (lines of equal air pressure) indicates the scope of the winds being generated by the huge new spring storm which has moved off the Pacific and is making its way Tuesday across the Rockies 
TUESDAY’S afternoon temps at 1pm CDT Tuesday 
TEMPS ARE HIGHER THAN 24 HOUR AGO across areas shaded in red on the 1pm CDT Tuesday analysis 
Dew points are a measure of atmospheric moisture. The green shaded Gulf moisture is shown sweeping north through Texas and Oklahoma and into Kansas and Missouri. 
HERE’S WERE WINDS WILL BE DELIVERING MOISTURE to the incoming spring storm system. This is the forecast for 4pm CDT Wednesday 
ANOTHER MEASURE OF MOISTURE through the lowest 30,000 ft. of the atmosphere is PRECIPITABLE WATER. This is the forecast of moisture and where it will be in place (shaded in green) at 1pm CDT Thursday 
This plot of JET STREAM WINDS at the 34,000 ft. level shows the powerful jet stream wind max racing off the Pacific in the West supporting the storm currently making its way across the Rockies. 
THIS UPPER AIR MAP for the 34,000 ft. level out of Environment Canada shows the jet stream wind max roaring off the Pacific in the western U.S. 
A 155 mph wind max is embedded in the jet stream winds coming off the Pacific into the western U.S. 
Here is the forecast of where those STRONG UPPER WINDS will be located later Thursday. T-storms can reach into the upper wind fields and direct wind energy to the surface as powerful wind gusts. 
The 5,000 ft. wind forecast for Thursday evening show the low level wind flow in place and delivering moisture to t-storms clusters which flare Thursday
Starting at 7 a.m. CDT Wednesday through 1 a.m. Friday
Precipitation probabilities Tuesday night Through Thursday
DAY #2 Wednesday/Wed. night STORM PREDICTION CENTER severe weather risk depicting a “MARGINAL RISK”
Day #3 SEVERE WEATHER RISK Thursday/Thur. night
The Approaching Warmth
FORECAST AIR TEMPS BY LATE WEDNESDAY showing the sharp increase in temps south of the northbound warm front. That front will have made its way to the South Side of Chicago by evening and will continue north across the rest of the Chicago area Wed night sending temps surging in Chicago and area north into the 60s.
This SURFACE WIND FORECAST shows how clearly wind mark the warm front’s predicted location by 5pm CDT Wednesday. The southern suburbs will have moved into warm southerly winds by Wed evening. At the same time, chilly southeast winds will be blowing off Lake Michigan from Chicago north into the North Shore and northern suburbs
SECONDARY STORM DEVELOPMENT is to sweep a chilly rain and strengthening northerly winds into the Chicago area Saturday. This is the NWS GFS ensemble model forecast panel for 7 am CDT Saturday through 1am CDT Sunday:
