Spring’s mild temps to be tempered near Lake Michigan by easterly weekend winds; gusty south winds Monday and Tuesday to deliver the warmest readings

The chilliest spring here in 17 years, a season responsible much of the past week for March-level 40-degree highs, finally relented Friday allowing more seasonable 60+-degree temperatures to sweep in on 30+ mph wind gusts.


Friday afternoon temperatures hit 67 at O’Hare and Midway and 66 at the lakefront—readings 16-degrees warmer than the low 50s recorded the day before. It marked the first time since Monday anything close to a seasonable late-April-level reading had occurred here.


The mild air spills into the weekend, though lakeside residents may not share the thermal bonanza to the degree their inland neighbors will.  That’s because easterly winds blowing around the northern flank of a downstate weather disturbance have replaced Friday’s southwest winds which pushed the warmth into lakeshore areas, overcoming lake cooling.


Predicted wind velocities aren’t likely to be particularly strong Saturday so the inland penetration of lake-cooled air isn’t likely to cover much real estate. But, the flow off chilly lake waters, which currently average 45-degrees, is likely to limit immediate shoreline highs to the low and mid 50s while 70-degree highs occur to the west in the warmest sections of DuPage, Will and McHenry counties westward to the Fox Valley, on to DeKalb and Rockford, and north into Wisconsin near Lake Geneva.


Warm-up welcome in chilly spring 2013 which has produced half the typical 60+-degree temps


Friday’s warm-up was a welcome development in a season which has seen nearly three-quarters of its temperatures coming in “below normal” since March 1.


The 67 at O’Hare marked only the 8th time in 2013 a daytime reading has made it above the 60-degree mark.  That’s far short—less than half—of the eighteen 60s Chicago’s official observational record suggests have occurred on average by April 27.


Warmth not limited to Chicago; 70s reach Minneapolis while mild air melts a foot of snow at Duluth


Warming across the nation’s Heartland was hardly restricted to Chicago. Temperatures hit 72 at Minneapolis Friday—that city’s first 60 and 70-degree reading.


In Duluth where late winter and spring snows have broken nearly every snow record on the books, the warm-up is responsible for melting 12” of that city’s deep snowpack over the past three days leaving 15” on the ground.


Ominous signs wetter pattern to re-establish later in the coming week


Model forecasts have taken a disturbing turn in their predictions for later next week into the weekend and week which follow.  A peculiar mid-continent upper storm system is predicted to take shape the second half of next week—a system apt to only crawl across the region because of strong upstream atmospheric blocking over eastern Canada. By inhibiting this potentially wet new system’s escape route to the east, the blocking pattern means the upper storm expected to “spin-up” over the nation’s mid-section could linger, generating waves of rainfall over a multi-day period.


Rainfall projections off Friday computer model runs suggest more than 1” of rain could fall in the coming 7-days alone—with several multi-week forecasts putting potential Chicago area rainfall in the 1 to 2.5” range.


Blocking patterns have often been involved in ratcheting up the intensity of storms and their impacts.  By slowing a system’s movement, as the predicted block will, the potential for big rainfall numbers rises. This is a development we’ll be monitoring in coming days.  Stay tuned!

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