Warmer days ahead for Chicago—we’ll break into the 60s away from Lake Michigan Wednesday afternoon and make it to the 70s by week’s end—though lake breezes will be cooling the shoreline—the weekend is to see organized east winds which will cool shoreline locations even as inland areas warm—but it appears we’ll be flirting to 80 by TUES/WED next week!
MAMMOTH SPRING STORM
Below normal temps moved into an 11th consecutive day Tuesday—featuring a sub-normal high of 54° and 31 mph wind gusts at O’Hare (Midway made it to 55° Monday). It marked the 5th day in which Chicago’s weather was controlled by the mammoth spring storm which has wreaked havoc over a wide swath of the Midwest and East coast—producing up to 29″ of snow the past two days followed by 1 to 3.70″ rainfalls in parts and 50+ mph wind gusts across a swath of Michigan’s Upper Peninsula; generating Monday’s deadly downstate I-55 downstate dust storm and forcing Chicagoans to keep a close watch on the sky for what little sun we’ve seen through fleeting breaks in the clouds.
LIMITED SUNSHINE IN CHICAGO SINCE LATE LAST WEEK
Friday saw only 18% of its possible sun; 21% Saturday; 40% Sunday; NO sun Monday and just 18% of our possible sun Tuesday. When the sun has appeared, its produced eye-catching rainbows. But the lack of sun has taken a toll on temps temps only reaching 48 Sunday, 50 yesterday and 54 Tuesday. Normal high temps this time of year are in the mid 60s.
BETTER NEWS ON THE TEMP FRONT IN COMING DAYS
The atmospheric blocking pattern, which has held the cloudy, showery spring storm system hostage and reduced its forward motion to a glacial speed, is to break down and critical North American upper level steering winds are about to undergo a sea change. This is going to permit warmer air over much of the country to our west to sweep eastward–and temps here will reflect the change.
BIG CHANGES ARE COMING AND WARMING WILL RESULT
Temps surge to the low 60s inland Wednesday (the lakefront will stay in the 50s); the mid 60s Thursday and low 70s Friday. Even warmer air is on tap next week with temps likely to flirt with 80-deg by Tuesday and Wednesday.
The influx of milder air in coming days will boost this week’s average temp by by nearly 5-degrees over last week with inland 60s predicted Wednesday and Thursday and low 70s Friday. NOTE: Winds off the lake will cool shoreline areas and our beaches, so it’s not likely we’ll be sunbathing this week. But compared to the temps we’ve experienced, what’s coming SHOULD FEEL MUCH WARMER. For the first time in more than a week, daytime highs will actually reach normal levels for the time of year Thursday and Friday.
Summer-like warmth expected by next Monday and Tuesday when temperatures will be near 80° both days
And warming next week is to be even more dramatic with a near 15-degree weekly increase predicted over this week. That’s a huge change—one which may permit daytime temps here to flirt with 80-degrees nextTuesday and Wednesday.
THE COOL WEATHER IS HARDLY COMPLETELY OVER
We’ve a got a chilly lake next to us here in Chicago and any time winds shift easterly, the cool air that floods ashore will make that evident. The lakeside cooling will be quite evident as an organized easterly flow sweeps into lakeside areas this weekend.
But a look at the May temp record here in Chicago shows since 1942, 99% of Mays have produced one or more 80-degree days; 94% have produced one or more 85-degree temps and 78% of Mays have produced one or more 90-degree days. In fact a year ago, May 12 saw first 90 here in Chicago—and that came after a chilly start to the month.
Warm Spells To Become More Frequent
There will still be cool spells—but the warm spells will begin occurring more frequently and with increasing strength as days continue to lengthen (we’ll pick up another 56 minutes of daylight between now and the end of the month) and as the sun treks across the sky farther above the horizon each day—meaning its rays will arrive more directly.
May is a month of more frequent warmth.
But lake water warm far more slowly which makes it a month of frequent cooling lake breezes too. Still, the past 8 decades have produced 80-deg temps on one or more days in 99% of years; an 85 deg temp in 95% of year and a 90-deg temp has even occurred in 78% of years. IN fact, just 9 days from today’s date—on May 12th last year—the city recorded its first 90-deg temp. Such warmth comes and goes until we get the lake warmer—but there temp progress in the cards for those awaiting warmer temps.
Slideshow of The Weather Situation
Tuesday afternoon GOES EAST weather satellite view of the slow moving spring storms responsible for the string of frequently cloudy, windy, unseasonably cool and sporadically showery set of days since last Friday here in Chicago. The storm produced the powerful winds responsible for the deadly I-55 dust storm Monday. Satellite image courtesy of CIRA-RAMBB 
Satellite derived precip from CIMSS (the Cooperative Institute for Meteorological Satellite Studies) at the University of Wisconsin-Madison. This analysis was produced Tuesday afternoon. 
Closer look at rains swirling around the huge spring storm centered in southern Canada Tuesday afternoon 
Mid Tuesday afternoon temperatures 
24 hour temp change comparing Tuesday and Monday afternoon temps 
The huge counterclockwise circulation around the slow moving spring storm dominating the winds blowing over most of the eastern half of North America Tuesday evening 
This dew point analysis show the most humid air over Texas and Florida. 
This 7am CDT TUESDAY UPPER AIR ANALYSIS depicts conditions at the 34,000 ft. (250 mb) level. The “wavy” steering winds have contributed to the huge temp differential across the continent. Meteorologists refer to this as a “highly amplified” pattern. Amplified pattern send jet stream winds north into the arctic–and then the flow dives southward with cool air in tow. It that’s cool air which has dominated in Chicago since the weekend—reinforced by the sun blocking cloudiness… See more 
The slow movement the spring storm which has played a role in Chicago’s weather since the weekend is the product of an ATMOSPHERIC BLOCKING PATTERN. The wavy wind pattern is oriented in the shape of the Greek alphabet letter “omega”–which is why this blocking pattern is referred to as AN OMEGA BLOCK. 
Forecast HIGHS WEDNESDAY 
Forecast HIGHS THURSDAY 
Forecast HIGHS FRIDAY 
Tuesday’s upper air pattern 
FORECAST UPPER FLOW 7pm CDT FRIDAY–The flow pattern is less wavy and more “zonal”—i.e. westerly. This is why warm air in the West and Plains is to stream eastward. 
FORECAST UPPER AIR 7pm CDT Sunday 
FORECAST UPPER AIR 7PM CDT A WEEK FROM FRIDAY 
Forecast AVERAGE 5-DAY TEMP DEPARTURES COVERING THE PERIOD from Wednesday through Tuesday 
Day 5 to 10 AVERAGE TEMP DEPARTURE FORECAST–showing the broad coverage of ABOVE NORMAL TEMPS over the eastern two thirds of the Lower 48. 
FORECAST HIGHS SUNDAY 
FORECAST HIGHS MONDAY 
FORECAST HIGHS TUESDAY 
FORECAST WEDNESDAY HIGHS TEMPS 
Series of surface weather maps–FORECAST 7PM WED–Isobars are widely separated suggesting a weak pressure gradient. When this happens, the cool dense air which hugs the Lake Michigan surface to flow inland as a late morning and afternoon LAKE BREEZE. The forecast maps which follow are generated by the European Centre’s ENSEMBLE MODEL–the “EPS”model 
FORECAST 7PM CDT THURSDAY–More tightly spaced isobars suggest a better developed southern flow will be shifting toward Chicago–which should boost afternoon temp i 
FORECAST 7pm CDT Friday evening forecast suggest a “SE” wind will be in place across the Midwest which will produce cooling along Lake Michigan even as inland areas warm into the low 70s Friday 
SATURDAY 7pm CDT FORECAST–A well developed east/southeast flow will be flowing into the city off Lake Michigan even as warm air dominates inland Saturday. 
FORECAST 7PM CDT Sunday forecast–The isobaric configuration suggests a well developed “SE” flow with warm temps inland (likely low 70s) and cooler reading on area beaches (low to mid 60s on Chicago lakeshore 
FORECAST 7pm CDT Monday–Warming is intact and likely buoyed by a more southerly flow by later in the day which reduces Lake Michigan impact on Chicago temps. Modeling suggests 60-deg dew points will have reached Chicago–which is more humid air than has been in a place for some 
FORECAST 7PM TUESDAY–Warm, moderately humid air is to spaces clusters of showers and possible t-storms 
TEMP TREND FORECAST off the National Weather Service’s GEFS model–an ensemble model. This projection reaches into the Day 1 to 5 time frame. Watch as the blue shaded BELOW NORMAL TEMPS DISAPPEAR as the model forecast moves further into the future 
DAY 6 to 10 TEMP DEPARTURE FORECAST showing the expansion of ABOVE NORMAL TEMPS 
DAY 11 to 15 TEMP DEPARTURES showing NEAR TO ABOVE NORMAL TEMPS in this time frame
Drier pattern in the wake of recent frequent bouts of showers
Rainfall amounts look to be pretty scant across the Chicago area through next Tuesda. Heaviest totals to focus on areas downstate and portions of Missouri
FORECAST RAINFALL TOTALS through next Tuesday evening:
