Another warm day for this final day of May 2023—with the warmth more noticeable because humidity’s were higher. Dew points, a measure or atmospheric moisture surged into the mid 60s versus the upper 40s 24 hour earlier. That’s a fairly BIG INCREASE and one that renders the air noticeably more “humid”–though hardly oppressively so. Mid 60-deg dew points constitute a “moderately humid” air mass. (70+-degree dew points would quality as more “oppressively” humid.

It was 2023’s second day with an official 90 degree temp—the same number of 90s we had seen by this time a year ago.

There was a big spread between the lakeshore and inland areas again today—with temps as warm 95 at Poplar Grove in Boone County, 94 at Barrington and 93 at Carpentersville and Warrenville—compared to a mid afternoon temp of 62 at the Wilmette Harbor buoy, 67 at Winthrop Harbor, 68 at the Lake Forest lakefront, 66 at the Kenosha, WI lakefront,74 at Calumet Harbor and 74 at the Michigan City, IN buoy. That means temps varied more than 30 deg between the Chicago area’s warmest and coolest locations.

T-storms bubbled up in the humid air and dropped brief but, as expected, scattered downpours whose rains have done little to allay concerns over the dry meteorological spring season we conclude with May’s close at midnight tonight. A few produced 40-50 mph wind gusts according to Doppler scans—but we estimate perhaps 30 to 40% of the Chicago area was visited by any rain and most of that was minimal and fleeting.

O’Hare picked up just a trace of rain Wednesday—which doesn’t change the month’s abysmal 0.42″ rain tally—an amount which means the month closes the 2nd driest May in Chicago of the past 153 years with only 10% of the month’s normal rain. Only May 1992 was drier with 0.58″ to its credit. And the full 3-month meteorological spring season has recorded 6.24″ of precipitation—59% of the normal tally and enough to qualify among the 14% of driest springs since official records began 153 years ago in 1871.

May finishes 2 degrees warmer than. normal and 1.3 degree cooler than May a year ago.

June begins tomorrow (Thursday) and is a month which opens with normal temps of 76/56—normally which warm to 84/65 by month’s end.

June is home to the northern hemisphere’s longest day (in terms of daylight) which will occur this year on June 21. Even though days begin to shorten very slowly later in June and through July and August, the warmest temps lag the longest day and typically occur later in July and linger into early August—so normal temps will continue rising this month and slow in July, beginning a slow season drop off in the latter half of August.

Much as happened today—but with slightly lower areal coverage—daytime heating and moderate humidity levels bring with them the potential for a few scattered t-storms “bubbling up” Thursday. Areal shower coverage may But rain chances diminish with modest drying of the air mass Friday which should push any shower development well west of Chicago. And a stronger easterly wind gradient sweeps drier, far more stable (i.e. less inclined to produce any shower development) this weekend into early next week. Dew points which have hit the mid 60s today lower to the mid 50s by Thursday afternoon and to the mid 40s to low 50s over the coming weekend—which is quite dry and not a level of moisture which makes rain a good bet at all.

Still no indication over the coming 2 weeks of a good general soaking rain. A bit of an increase in rain prospects is noted toward mid-month—but estimates of 2 week total rainfall here puts the per cent of normal rainfall at just 47%–i.e. less than half—even with the mid-month increase.

A brief cool down is predicted by mid next week—but there are signs warmth will rebuild again by late next week and the following weekend. This week is to average nearly 9-deg above normal—and next week, even with the mid-week downturn—is still predicted to come in with a 3-deg surplus.


TONIGHT: A few lingering but low coverage showers fade away. Then clouds scatter and warm with lighter winds. Low 69.

THURSDAY: Sunshine amid some rebuilding cottony cumulus clouds, very warm inland—but with cooling lake breezes. Re-develop of some comparatively low coverage scattered showers or t-storms expected by afternoon but impacting only 20 to 30% of the metro area. High 91 inland—but mid 60s to mid 70s along Lake Michigan.

THURSDAY NIGHT: Showers diminish and clouds scatter. Warm and calm. Low 68.

FRIDAY: Mostly sunny, continued warm away from the lake. High 90 inland—but mid 60s to low 70s lakeshore,

SATURDAY AND SUNDAY: Rain-free with mostly sunny, warm days; and scattered clouds at night. High Saturday 84; Sunday’s high 80—but 60s lakeshore.

MONDAY: Partly sunny and warm. Lake breezes continue. High 85—mid 60s to low 70s beaches.

TUESDAY: More clouds, not as warm. High 80—60s lakeshore.

WEDNESDAY: Partly sunny. High 79—but 60s beaches.