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  • Tim McGill

Are Chicago's Summers Stretching More Into Fall?

Summer Sticking Around Longer

We started off October with five straight days below average but today will be the fourth straight day above average. That above average streak could continue through early next week. Today will be the warmest day we will see for at least the next ten days. Some sun combined with a gusty southwest breeze should push our highs into the lower 80s. That is about 15° above average.

An 80° high this far into fall is becoming more common. The heat of summer has been spilling over more and more into fall. Summer is effectively stretching out further into the year and delaying the start of fall. This is happening across most of our country. Climate Central did a study of 242 cities and their analysis shows 77% of those cities recorded their last day of summer-like weather an average of three or more days later since 1970. Half of the cities analyzed stretched their summer-like temperatures a week or more longer into the year.

Southern cities had the longest extension of summer-like weather with some cities stretching the season up to three weeks or longer into the year.

Their analysis considered the last calendar day when temperatures reached their average daily summer high. The stretching of Chicago's summer further into fall was not as dramatic but still significant. Summer-like temperatures here are extending into the year about 2 days later compared to 1970. The average date of the last 80° high here is now on October 4th.

A longer summer has some consequences. Climate Central's study noted several:

The intrusion of summer warmth into colder seasons presents a significant challenge for native plant and animal species whose life cycles are scheduled around the once-reliable seasonal changes. For instance, natural tactics to withstand cold temperatures (known as ‘overwintering’) are pushed back, meaning later migration, hibernation and leaf drop.

A longer frost-free season spells trouble for allergy sufferers, but it could mean more time for growing and harvesting crops ーan average of two extra weeks since 1970. While this may be a possible benefit to some farmers and crops in some locations, there are numerous other impacts of climate change on agriculture such as water stress, depleted crop yields, and risks for farm workers due to excessive heat, and losses from increases in extreme weather events.

Colder temperatures are what keeps many pest and invasive species at bay, so retreating cold could also favor the survival of more mosquitoes, ticks (and the diseases they carry), as well as crop pests and weeds.

Sunshine Through Smoke

Today's highs may be held back a degree or two by some smoke aloft. Instead of bright blue skies today the sun might take on more of a milky appearance. I mentioned yesterday that we needed to watch the wildfire smoke forecast for today. The HRRR vertically integrated smoke forecast has western wildfire smoke riding the jet stream eastward into the midwest today. The smoke is aloft but higher concentrations are forecast for northern Illinois and northern Indiana.

Cooler Pattern Coming?

Highs should be at least near 70° or warmer after today through Monday. Our pattern may be shifting in favor of cooler weather beyond that as we get into the middle of the month. The 6-10 day temperature probability forecast has us outlooked for normal or near normal temperatures overall from October 14th through the 18th. The 8-14 day forecast has us outlooked for below average temperatures overall from October 16th through the 22nd.

Drought Diminishes Here But Not Downstate

Rainfall is now -.47" below average for October and -.50" below average since September 1st. The latest US Drought Monitor assessment shows the moderate drought that had creeped into portions of northern Illinois has now disappeared. Despite that the moderate drought has expanded overall across the state. The area in a moderate drought downstate has nearly tripled from 3.69% of the state last week to just under 12% this week.

The longer range forecast is mainly dry. There is a slight chance for a spotty shower or some drizzle later Saturday into early Sunday. The best chance of rain is later Monday into Tuesday.

The longer range forecasts keep us fairly dry through the middle of the month.

Both 6-10 day and the 8-14 day 0recipitation probability forecast has us outlooked for below normal precipitation overall from October 14th through the 22nd.

Here is my 7 day forecast:

Today: Partly to mostly sunny, warm & breezy High: 81

Saturday: Partly to mostly cloudy Low: 63 High: 74 (temps falling pm)

Sunday: Partly mostly cloudy Low: 56 High: 72

Monday: Partly cloudy, a few scattered showers (t-storm possible) Low: 62 High: 72

Tuesday: Mostly sunny Low: 49 High: 69

Wednesday: Mostly sunny Low: 47 High: 65

Thursday: Partly to mostly cloudy, shower possible Low: 45 High: 61



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