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  • Tim McGill

Above Average All Week

Fall Back On Hold

Sunset On The Chain Of Lakes Sunday Night

Sunday was yet another warmer than average September day. 18 out of 27 days this month have been above average. Yesterday's high of 83° was 12° above the average of 71° for late September. So far this September is the 5th warmest on record for Chicago.

Meteorological fall will be four weeks old by the end of today but it has rarely felt like fall since it started on September 1st.

The HRRR Model has our highs today topping out in the middle to upper 80s. Those are typical temperatures for the middle of July. A cold front this afternoon will sag south out of Wisconsin and temperatures will tumble quickly. The could fall around 10° to 15° in just an hour or two.

A cooler wind off the lake will kick in with the arrival of the cold front. Tuesday should be around 10° to 15° cooler than today. The GFS Model has highs Tuesday sliding back into the 70s. Lower 70s are expected along the lakefront with middle 70s further inland.

The wind shift will start in our northern suburbs early this afternoon and then work south through the rest of the day. Watch for a sharp drop in temperatures from the 80s to the 60s by the evening.

Winds will shift from the southwest to the northeast and off the lake and stay there through Tuesday.

A fairly strong northeast wind will bring some danger to the shoreline of Lake Michigan late this afternoon into early Tuesday afternoon. A beach hazards statement is in effect from 4 pm today until 1 pm Tuesday.

Winds will whip up big waves and generate dangerous currents. Swimming conditions will be life threatening.

Staying Relatively Warm Thru The Weekend

Even though we will cool off after today we will stay above average all the way through Sunday. The National Blend Of Models shows today will be the warmest day of the week. Average highs are around 70° to 71° this time of the year. We should stay above that for seven straight days.

Today and Wednesday will see highs particularly warm as they climb into the 80s. The temperature anomaly forecast has temperatures Wednesday around 10° to 15° above average for most of the Midwest.

Once again there is a very strong signal for a warmer than average pattern in the longer range temperature outlooks. The 6-10 day outlook has Chicago favored for above average temperatures overall from October 2nd through October 6th. The longer range 8-14 day forecast also favors us for above average temperatures overall. It covers the period from October 4th through October 10th. For both forecasts we are in the 60-70% probability range. 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.

Relatively Dry Pattern To Persist

O'Hare is now down 1.57" below average for September rainfall. The next decent chance of rain doesn't come until the weekend and even then, the forecast is for generally light amounts. So it appears the drought will deepen again this week.

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 doesn't have any rain in the forecast until Friday but a better chance late Saturday.

The GFS model's total precipitation forecast through the weekend suggests most of us will pick up around a third of an inch of rain. Lighter amounts are forecast for areas well northwest of the Chicago and slightly heavier amounts south and southeast of the city.

Still nothing encouraging in both of the longer range precipitation outlooks. The latest 6-10 day forecast has the Chicago area favored for below average rainfall from September October 2nd through October 6th. The longer range 8-14 day forecast has us outlooked for below average precipitation too from October 4th through October 10th.

Here is my 7 day forecast:

Today: Mostly sunny, breezy High: 85 (turning cooler late)

Tuesday: Partly to mostly sunny Low: 61 High: 76 (72 lakeside)

Wednesday: Mostly sunny Low: 57 High: 82 (78 lakeside)

Thursday: Mostly sunny Low: 58 High: 77

Friday: Mostly sunny Low: 61 High: 76

Saturday: Partly to mostly cloudy, sct. showers possible Low: 59 High: 76

Sunday: Partly to mostly sunny Low: 58 High: 74


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