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  • Tim McGill

October Starts Out Feeling Just Like July

Top 5 Warmest September

It was the warmest September in half a century and the 5th warmest on record for Chicago. The average temperature for the month was 70.3° which was 4° above average.

Summer-like warmth is now spilling over into October. Today will be the 6th straight day with temperatures above average and the third straight day with a high of 80° or warmer.

We start off the second month of meteorological fall with highs around 15° above average. Today's temperatures are typical for the middle of July.

The HRRR Model has our highs climbing into the middle 80s for most of the area. A light breeze off of Lake Michigan will hold temperatures along the immediate lakefront in the upper 70s. Well away from the lakefront we could see highs in the upper 80s. Average highs for today's date are around 70°.

Some spots could tag 80° on Saturday. The GFS Model has highs tomorrow topping out in the lower 80s. I think the additional cloud cover and occasional showers will hold most of us in the upper 70s.

GFS Model Forecast Temperatures For Saturday Afternoon

Despite cooling off this weekend and next week we should stay above average for the next several days. Jumping ahead to a week from Sunday with the temperature anomaly forecast shows unseasonably warm air is still sticking around. Northern Illinois is forecast to be between 20° to nearly 25° above average. The average high for a week from Sunday is 65°. This might be a bit overdone but if this even closely verifies, it will be rather warm for the Chicago Marathon.

A wind shifting to the south/southwest will pump the unseasonably warm air our way this weekend.

It will not only be a warmer than normal weekend it will also be a bit more muggy. Dew points remain pleasant today but jump into the 60s early Saturday.

The best chance of rain on Saturday is from the middle of the afternoon through the evening and overnight into Sunday.

We've seen moderate levels of wildfire smoke aloft the past couple of days and that doesn't change today. The HRRR Model vertically integrated smoke forecast shows a "blob" of moderate concentrations of smoke sitting over the Midwest this afternoon. Like yesterday, this could mean a more "milky" look to the sun and help to give our sunset an orange-reddish hue.

Overall Relatively Warm Pattern Sticks Around

The National Blend Of Models has our highs in the 80s today and tomorrow and then slipping back into the 70s Sunday. It cools us off into the lower 70s early next week and then gradually warms us up through the end of the week into next weekend. Each of the next ten days is forecast to be at a few degrees above average.

The warm signal from the longer range temperature outlooks continues. The middle of this new month should be relatively warm. The 6-10 day outlook has us favored for above average temperatures overall from October 6th through October 10th. The longer range 8-14 day forecast also favors us for above average temperatures overall. It covers the period from October 8th through October 14th. Average highs for this period are in the middle to upper 60s.

The even longer term 35 day temperature anomaly forecast still has a fairly strong warm signal for the Midwest and most of the country all the way through October and into the start of November. We are outlooked to be between 4° to 6° above average overall for the period from September 28th through November 2nd. 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.

A Wet First Weekend Of October

Some much needed rain for parched portions of northern Illinois will fall this weekend. It won't be a washout but it will be wet at times with occasional showers and a few rumbles of thunder.

Our lawns in Lake and McHenry counties are crying out for some rain. O'Hare ended up 1.96" of rain below average for September. The drought has deepened this week.

The latest US Drought Monitor analysis shows just how much the drought has deepened. The areas in a severe drought (level 2 out of 4) and extreme drought (level 3 out of 4) areas have more than doubled compared to last week. The area in a moderate drought increased slightly. Northern Illinois is being hit the hardest by the drought.

A side-by-side comparison shows the change between September 28's drought conditions and the prior analysis back on September 21st.

Drought Conditions On 9/28 (Left Image) Vs. 9/21 (Right Image)

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.

The drought news was also discouraging for the Midwest as a region. The areas in a moderate, severe and extreme drought all expanded.

An analysis of the past 30 days of rainfall (ending on September 30th) reveals just how dry it has been. Most of our northern Illinois has seen between 10% to 50% of average rainfall during this period.

The GFS model's meteogram for O'Hare shows periods of scattered showers with the possibility of a few thunderstorms later Saturday, Saturday night and during the day Sunday. Little rain expected after this weekend until a week from Sunday.

The GFS model's total precipitation forecast through Monday morning suggests we could squeeze out some decent rainfall. It suggests about a half inch to just over an inch of rain is possible.

Not much hope for help with the drought offered in the longer range rainfall outlooks. The latest 6-10 day forecast has the Chicago area favored for below rainfall from September October 6th through October 10th. The longer range 8-14 day forecast also has us outlooked for near normal precipitation from October 8th through October 14th.

Here is my 7 day forecast:

Today: Sunny, unseasonably warm, pleasant High: 85 (78 lakeside)

Saturday: Partly to mostly cloudy, sct. showers (isolated t-storms possible) Low: 63 High: 79

Sunday: Mostly cloudy, scattered showers (isolated t-storms possible) Low: 64 High: 75

Monday: Scattered showers early, partly to mostly cloudy Low: 60 High: 70

Tuesday: Partly to mostly sunny Low: 59 High: 70

Wednesday: Partly to mostly sunny Low: 59 High: 72

Thursday: Partly to mostly sunny Low: 60 High: 74


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