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  • Tim McGill

Not Done With The 80s

Cooler Today But Above Average

It wasn't just a warm start to the week on Monday, it was hot by late September standards. O'Hare hit 87°, 16° above average. Rockford hit 90° to break a record that went back more than 60 years. Midway and Aurora hit 88°.

These aren't the type of temperatures you expect during meteorological fall. 19 of the first 28 days of autumn have been above average. September is now running just under 4° above average.

The GFS Model has us cooling off by 10° or more today. Highs today should top out in the middle 70s for most of us which is still above the average high of 71°. Our wind off the lake will keep it cooler lakeside with highs there in the lower 70s.

We aren't done with the 80s. The GFS Model has highs Wednesday warming into the lower 80s. The wind continues off the lake so highs lakeside will be cooler. Look for highs along the lakefront in the lower 70s.

A quiet pattern continues through the end of the week. The wind stays off the lake today and tomorrow. Virtually no chance of rain through Wednesday but that could change by the weekend. More on that further down in this post.

A beach hazards statement is in effect until 1 pm today. Life threatening swimming conditions are expected along the southern shoreline of Lake Michigan. A combination of big waves and dangerous currents means a high swim risk into early this afternoon.

Waves could be as high as three to five feet early today before subsiding during the afternoon.

Riding This Warm September Wave

We should stay above average through the weekend. The National Blend Of Models shows our highs sliding into the middle 70s today. Average highs are around 70° to 71° this time of the year. We could hit a high of 80° or more Wednesday, Thursday and Friday.

The temperature anomaly forecast for Wednesday shows the Midwest having the biggest jump above average. Most of the Midwest will be between 10° to 20° above average. Parts of northern Minnesota could be nearly 30° above average.

The vast majority of the country is outlooked for a relatively warm first part of October and that includes the entire Midwest. The 6-10 day outlook has Chicago favored for above average temperatures overall from October 3rd through October 7th. The longer range 8-14 day forecast also favors us for above average temperatures overall. It covers the period from October 5th through October 11th. Average highs for this period are in the upper 60s to lower 70s.

The even longer term 30 day temperature anomaly forecast has a strong warm signal for the Midwest and most of the country for the period covering the last week of September through just over the first three weeks of October. We are outlooked to be between 4° to 8° above average overall for the period from September 24th through October 24th. 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.

Rain May Return Late This Weekend

O'Hare is now down 1.67" below average for September rainfall. Models are hinting at some rain by the end of this weekend. That's good news but for now the drought continues to deepen in northern Illinois.

I reviewed the latest US Drought Monitor analysis on Friday. Here is a recap:

The latest US Drought Monitor analysis has bad news for Illinois. The moderate drought (level 1 out of 4), severe drought (level 2 out of 4) and extreme drought (level 3 out of 4) areas have all increased since last week. Northern Illinois is the only portion of the state in a drought with the worst conditions in Lake County.

Here is a summary of the impacts the ongoing drought is having on northern Illinois from the National Weather Service:

Volunteer observers across far northern Illinois indicate much lower then typical stream flows on area creeks and rivers, particularly along Beaver Creek and the Kishwaukee River.

Reports also indicate that lawns have gone dormant and there has been some stress to the trees. Few impacts to agriculture have been received recently, though the dry conditions and stressed crops have resulted in an early start to the harvest season across northern Illinois. Data available from the Illinois State Water Survey, USGS, and NCEP indicate that soil moisture, groundwater, and surface water levels remain below normal.

An analysis of the past two weeks of rainfall (ending on September 26th) reveals just how dry the past couple of weeks have been. Most of the Chicago area has seen just 25% to 75% of average rainfall.

The GFS model's meteogram for O'Hare hints at some light rain Friday afternoon but a better chance on Saturday. It squeezes out more rain later Sunday into Monday. The European model brings the rain in later Sunday with lighter amounts compared to the GFS model.

The GFS model's total precipitation forecast through the next Tuesday offers hope of picking up around a quarter to a half inch of rain in total.

Still looking at an overall dry outlook in the longer range forecasts. The latest 6-10 day forecast has the Chicago area favored for below average rainfall from September October 3rd through October 7th. The longer range 8-14 day forecast has us outlooked for below average precipitation too from October 5th through October 11th. The only good news is the signals aren't as strong as they have been in recent forecasts.

Here is my 7 day forecast:

Today: Becoming sunny, a bit breezy High: 75 (70 lakeside)

Wednesday: Mostly sunny Low: 58 High: 82 (73 lakeside)

Thursday: Partly to mostly sunny Low: 59 High: 80 (75 lakeside)

Friday: Mostly sunny Low: 60 High: 80 (76 lakeside)

Saturday: Partly to mostly sunny, sct. shower possible late Low: 60 High: 76

Sunday: Mostly cloudy, scattered showers Low: 60 High: 74

Monday: Mostly cloudy, scattered showers Low: 59 High: 70


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