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  • Tim McGill

Summer-Like Weather Sticks Around

Earth Had A Fever In August

Earth just saw it's sixth-hottest August on record dating back to 1880. The month came in globally 1.62° above average. Earth has had a fever for quite a while. This marks the 440th consecutive month with temperatures, at least nominally, above the 20th century average. NOAA’s report from the National Centers for Environmental Information shows August's heat was seen more on land than ocean areas.

Here's more from the report:

The Northern Hemisphere had its warmest summer on record at 1.17°C (2.11°F) above average, surpassing the now second-warmest such period set in 2016 and again in 2019. The five warmest summers for the Northern Hemisphere have occurred since 2015. Meanwhile, the Southern Hemisphere winter temperature of 0.67°C (1.21°F) above average tied with 1998 as the fifth warmest winter in the 141-year record.

Earth's warm August makes it virtually certain that 2021 will rank among the 10 warmest years on record. The year is 95% likely to fall in the range of sixth- to seventh-warmest on record.

Speaking of summer....

After five straight days with a high of 80° or warmer, we had a brief break from the heat Wednesday with a high of 79° at O'Hare. We will start another streak of 80° days starting today that could stretch to six in row when it ends early next week. Our meteorological fall so far is running about 3° above average.

The HRRR model has our highs reaching into the lower 80s most of us today. A breeze off the lake will keep it cooler along the lakefront with a high in the upper 70s there. The average high for today's date is 76°.

The GFS Model has our highs flirting with 90° Friday. That is nearly 15° above average.

GFS Model Forecast Temperatures For Friday Afternoon

A cold front crosses through Friday night and sets up a cooler Saturday with highs in the lower 80s but we bounce back quickly by the end of the weekend. Our highs Sunday will soar to near 90°.

Most of the country will be baking in unusually warm temperatures on Sunday. The temperature anomaly forecast has most of the Midwest about 10° to nearly 20° above average. Parts of the plains will be nearly 30° above average.

While we will be warmer today than yesterday and nearly 5° above average it will still be pleasant in terms of humidity. Our dew points jump back into the 60s on Friday for a more muggy end to the week.

A wind off the lake will keep us cooler today along the lakefront with highs there in the upper 70s. Our winds shift to the southwest early Friday morning bringing in more heat and humidity. Notice the winds shifting yet again Friday evening. This time they shift to the northwest to bring in cooler air for Saturday.

The best chance of rain is Friday evening into Friday night but only scattered showers and possibly an isolated thunderstorm are possible.

Wildfires smoke was swept out of our skies yesterday as cooler Canadian air pushed it well south of the city. Only light concentrations of smoke aloft are expected to waft back into the area today with a plume of thicker smoke staying to our northwest The HRRR Model vertically integrated smoke forecast for this afternoon shows a band of thicker smoke from California to northern Minnesota.

The National Blend Of Models has highs in the 80s for five of the next six days. I actually think we will have 80s for six of the next six days. I am forecasting Saturday's high to reach the lower 80s. Fans of cooler fall weather will have to wait until next Wednesday before highs slide back into the 70s.

The signal is weakening just a bit but the longer range temperature probability forecasts continue to suggest a warmer than average end to September. The 6-10 day forecast has outlooked Chicago for above average temperatures overall from September 21st through September 25th. The longer range 8-14 day forecast also favors us for above average temperatures overall from September 23rd through September 29th. Average highs for this period are in the lower to middle 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.

Dry Start To Fall

O'Hare has only seen .01 of rain for the first 15 days of fall. The month is now running 1.62" below average. There has been less than a third of an inch of rain there in the past three weeks. There is a chance for rain Friday evening and night but it will be scattered and not very heavy. I will have the latest drought analysis from the US Drought Monitor this Friday.

Here is a recap of our drought conditions that I posted last 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 14th) has been lacking. Most of the Chicago area has seen between just 10% to 50% of average rainfall during the period. Some suburbs west and south of the city and a portion of the city itself as only seen just 10% to 25% of average rainfall. Portions of northern Indiana has seen just 5% to 10% of average.

The latest GFS model has some scattered showers and thunderstorms late Friday into early Saturday but the amount of rain expected isn't impressive. There is a better chance for more significant rain Tuesday.

The GFS model total precipitation forecast through this weekend isn't very impressive. The rain shown here would fall late Friday into early Saturday. Most of us would see little to no rainfall if this forecast verifies but a few spots well west of the city might pick up nearly a quarter inch of rain.

The longer range rainfall forecast flip flops from above average to below average during the end of September. The latest 6-10 day forecast has the Chicago area favored for above average rainfall from September 21st through September 25th. The longer range 8-14 day forecast has us outlooked for below average precipitation from September 23rd through September 29th.

Here is my 7 day forecast:

Today: Mostly sunny, warmer but pleasant High: 82 (78 lakeside)

Friday: Mostly sunny, evening shower or t-storm? Low: 65 High: 87

Saturday: Becoming mostly sunny Low: 67 High: 81 (cooler lakeside)

Sunday: Mostly sunny Low: 67 High: 89

Monday: Partly to mostly sunny Low: 68 High: 85

Tuesday: Partly to mostly cloudy, scattered showers & thunderstorms Low: 69 High: 82

Wednesday: Partly to mostly sunny, scattered showers Low: 63 High: 77


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