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  • Tim McGill

Sunny Saturday But A Soggy Sunday

A Weekend That's Half Bad

Our warm fall pattern is coming to an end. 39 of the past 52 days this autumn have been above average. Yesterday was only the second day this month to be below average. Friday's high of 56° at O'Hare was the coolest high since late May. The low this morning of 39° at O'Hare was the coldest in over five months. Aurora dropped to 29°.

If October ended on Friday, it would rank as the 2nd warmest on record. Of course we have another week to go and it appears we will close out the month cooler with temperatures around our just a bit below average.

Average highs for today's date are around 60°. Even with plenty of sunshine expected we will fail to make it out of the 50s for highs today. The HRRR model has our temperatures topping out in the middle 50s this afternoon.

The relatively cooler pattern keeps coming. The GFS Model has our highs Sunday only in the middle 50s with temperatures falling into the 40s late in the day well northwest of the city.

Today will feature mostly sunny skies and light breezes. Sunday will turn soggy with strong winds off the lake. Both days will see highs in the middle 50s.

Winds will gust over 30 mph beginning late tomorrow and stay strong into early Monday.

Rain chances ramp up on Sunday by midday with the best chance late in the afternoon and through the night Sunday into Monday morning.

The gusty winds off the lake will whip up some big waves by early Monday morning. Waves could build to around 8 to 10 feet. The biggest waves would target Lake Michigan's shoreline just north of the city and along the Wisconsin border.

Cool Pattern Settles In

We can say so long to the 70s we saw early last week and according to some models, we maybe saying so long to the 60s for at least the next several days. The National Blend Of Models has our highs holding in the middle to upper 50s for the next eleven days in a row. Average highs fall from 60° today into the upper 50s on Sunday so this forecast is actually fairly close to average for late October.

The signal from the longer range temperature outlooks continues to weaken but still suggests we are leaning towards a mild pattern overall form the end of this month and through the first five days of November. The 6-10 day outlook has us favored for above average temperatures overall from October 28th through November 1st. The longer range 8-14 day forecast favors us for above average temperatures from October 29th through November 5th. Average highs for this period are in the middle to upper 50s.

The longer term 35 day temperature anomaly forecast has the middle of the country including most of the Midwest favored for a milder than average pattern. We are outlooked to be between 1° to 3° above average overall for the period from October 21st through November 25th. 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.

Soggy Sunday & Monday Then Drying Out

We started out October with an active pattern and a surplus of rainfall through the first couple of weeks. The pattern has become more dry as of late. In the last 9 days there has been less than two tenths of an inch of rain at O'Hare. O'Hare is now down 2.27" below average since the start of fall on September 1st. We could make up a lot of that deficit tomorrow into Monday. More on that below.

The most recent US Drought Monitor analysis was released Thursday. It was the second report in a row to bring mostly good news for Illinois. Here is a recap:

The area in at least a moderate drought (level 1 our of 4) dropped dropped slightly compared to the previous analysis. The area in an at least severe drought (level 2 out of 4) did not change. The only big of discouraging news is the area consider "abnormally dry" jumped by almost 25%. That is the area most likely to slip into at least a moderate drought if conditions don't improve.

It's hard to see much change when looking at the side by side comparison of this week's Illinois drought map next to last week's. The only thing that stands out is the growing area of yellow or "abnormally dry" conditions.

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 Midwest receive more good news. Every drought category saw a reduction in area. The biggest drop was for portion of the region in an extreme drought. It was reduced by more than half compared to the last analysis.

We started off October relatively wet but have dried up a bit the past. Including today, the past seven days have seen less than two tenths of an inch of rain yet most of northern Illinois has an above average surplus of rain to this point. Most of the Chicago area has received between 110% to 200% of average rainfall so far this month. There are even a few spots with over 300% of average thus far this October.

The GFS model's meteogram for O'Hare shows a soaking rain developing on Sunday and spilling over into Monday. Another round of rain is forecast starting Thursday and continuing on and off into early next Saturday morning.

The GFS model's total precipitation forecast through Monday squeezes out anywhere from an inch of rain well northwest of the city to around two inches in Chicago and nearly three inches south of the city.

The European model has similar numbers but overall is squeezing out a little less rainfall. It suggests around one to two and a half inches in total from Sunday through Monday.

After our soggy Sunday we could be looking at our pattern becoming more dry as we end October and begin November. The latest 6-10 day forecast has the Chicago area favored for about average rainfall from October 28th through November 1st. The longer range 8-14 day forecast has us outlooked for below average precipitation from October 30th through November 5th.

Here is my 7 day forecast:

Today: Mostly sunny, cool, light breezes High: 56

Sunday: Cloudy, rain develops, sct. t-storms possible, gusty winds Low: 43 High: 55

Monday: Cloudy, windy, on & off rain Low: 49 High: 55

Tuesday: Mostly sunny Low: 42 High: 56

Wednesday: Partly to mostly cloudy, sct. showers possible late Low: 42 High: 59

Thursday: Mostly cloudy, showers likely Low: 47 High: 58

Friday: Mostly cloudy, sct. showers Low: 48 High: 57


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