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  • Tim McGill

Feeling Like The Middle Of Summer In September

Warm Forecast From Short To Long Term

Saturday's blog post focused on the way fall is squeezing out more summer-like weather. Today's forecast for this week and all the way into the middle of October is for an overall warmer than average pattern. This week's temperatures will be more typical for the middle of summer. It might be meteorological fall but it certainly won't feel like fall this week.

The week starts out warm today for most of us. HRRR Model has a range of high temperatures from the middle 70s north of the city to the lower 80s in Chicago and the middle 80s south of the city. A frontal boundary will be stretched across our far northern suburbs with much of Lake & McHenry counties on the cooler side of the front. The average high temperature for today's date is 77°.

The frontal boundary will nudge north tonight and everyone will get in on some mid-September heat Tuesday. Highs tomorrow will be near 90° in most areas.

O'Hare's high on both Saturday and Sunday this past weekend hit 87°. This upcoming weekend may be just as warm. The temperature anomaly forecast has most of the country this Saturday above average. Parts of the Midwest and plains will be 20° to 25° above average. We should be around 10° to 15° above average here which means highs this weekend at least in the middle 80s.

A breeze off the lake and more cloud cover will keep us a bit cooler than what we saw this past weekend but still above average. Highs today will reach into the lower 80s for most areas but cooler lakeside and across our far northern suburbs with upper 70s there.

Gusty southwest winds will sweep in warmer air Tuesday. Gusts will approach 30 mph.

There is a chance early today for a scattered shower and thunderstorm near the Wisconsin state line but most of us should remain dry. The best chance of rain between today and tomorrow is later tomorrow afternoon. That's when a few storms could become severe. More on that below.

Thicker wildfire smoke aloft wafted back into our skies this weekend. The HRRR Model vertically integrated smoke forecast still has some moderate to high levels of smoke here at least through early this afternoon.

The National Blend Of Models has only one day this week around average. Wednesday's high of 77° is the coolest day forecasted of the next several. Eight of the next eleven days will see highs into the 80s.

Today's longer term temperature probability forecasts may collectively have the highest probabilities in favor of warmer than average temperatures so far this year. The 6-10 day forecast has outlooked Chicago for above average temperatures overall from September 18th through September 22nd. The probability is 80% to 90% for above average temperatures during the period. The longer range 8-14 day forecast also favors us for above average temperatures overall from September 20th through September 26th. The probability is also between 80% to 90%. Average highs for this period are in the middle to upper 70s.

The short term, longer term 6-10 day and 8-14 day) and the even longer 30 day forecasts are all in sync suggesting a warmer than average pattern. The Global Ensemble Forecast System (GEFS) is a weather forecast model made up of 21 separate forecasts, or ensemble members The model tries to give an idea of the amount of uncertainty in a forecast by running an ensemble of multiple forecasts which are each tweaked a bit with their initial conditions. The GEFS has the Midwest and most of the country outlooked for above average temperatures overall all the way into the middle of October.

Still Looking For Some September Rain

O'Hare has picked up just .01 of rain so far this September. The month is now running 1.32" below average. There has been less than a third of an inch of rain there in the past 18 days. Just one day of the next eleven looks promising for some rain. It appears the drought across our northern suburbs will deepen.

Here is a recap of our drought conditions that I posted on Friday:

The US Drought Monitor analysis shows a slight decrease in the area under a moderate drought ( 1 one out of 4 levels). The area shrunk from 9.96% to 9.81% compared to a week ago. The areas in a severe drought (level 2 out of 4 levels) did not change and remains at .79%.

Every drought level dropped for the Midwest region. The area under an exceptional drought, the most dire drought category, dropped form 1.15% to .99%.

The past two weeks of rainfall (ending on September 12th) have been rather dry. Most of the Chicago area has seen between 10% to 75% of average rainfall during the period. Our far western suburbs, a small portion of the city, southern Cook County and much of northern Indiana saw just 10% to 25% of average rainfall.

The latest GFS model has the best chance of rain over the next ten days coming later tomorrow in early Wednesday. Scattered showers and thunderstorms are expected and some could be strong, especially south and east of the city.

The GFS model total precipitation forecast through next weekend only squeezes out a tenth or two of an inch of rain for most of us. Higher amounts are possible in northern Indiana but some of us might not see much rain at all. Most, if not all of the rain shown here would fall later Tuesday into early Wednesday.

The Storm Prediction Center has placed our northern suburbs are in a marginal risk (level 1 out of 5) area for severe weather. The greatest threat would be damaging winds and hail late tonight into early Tuesday morning.

The Storm Prediction Center has placed most of the area in a marginal risk (level 1 out of 5) area for severe weather Tuesday into early Wednesday. There is a slight risk (level 2 out of 5) for severe storms well south of the city and into northern Indiana during this period. The greatest threat would be damaging winds and hail but a few tornadoes can't be ruled out.

A marginal risk is level 1 out of 5 possible risk levels. It is the low end of the risk categories but means "an area of severe storms of either limited organization and longevity, or very low coverage and marginal intensity".

A slight risk is level 2 out of 5 possible risk levels. It means the possibility of "an area of organized severe storms, which is not widespread in coverage with varying levels of intensity".

The longer range rainfall forecast keep us near normal initially and then trend us towards above average rainfall. The latest 6-10 day forecast has the Chicago area favored for about average rainfall from September 18th through September 22nd. The longer range 8-14 day forecast favors us for above average precipitation from September 20th through September 26th.

Here is my 7 day forecast:

Today: Mostly cloudy, warm High: 82 (78 north & along lakefront)

Tuesday: Partly to mostly cloudy, pm sct. showers/t-storms Low: 72 High: 87

Wednesday: Partly to mostly sunny, cooler Low: 65 High: 78

Thursday: Mostly sunny Low: 61 High: 82 (cooler lakeside)

Friday: Mostly sunny Low: 65 High: 86

Saturday: Mostly sunny Low: 66 High: 87

Sunday: Mostly sunny Low: 66 High: 88


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