Fall Temperature Recap

Temperatures from mid September to mid October have been well above normal. The warm autumns have been more frequent over the last 10 years than in years past. In fact, last year between Sept 15 and Oct 15 was WARMER than this year!

There have been only a few years (2025, 2024, 2017 and 1986) where the last half of September was warmer than the first half.

 Temperatures vs normal across the US:

Overall upper level pattern across the US:

Rainfall has been well below normal until the last 2 weeks of October:

Our last day above 80 was October 18. Since the 19th, temperatures have been below normal.

Is This late Summer Cool Period Unusual?

Summer is ending on a cool note across northern Ohio and surrounding states after a very humid start to summer through July (see previous post).  August ended up being far less humid across the Ohio Valley vs the June/July period. It was still very humid especially the first half of the month but not historic.

June and July was the most humid on record for northern Ohio. Yet the June through August period ended up being the 6th most humid in northern Ohio.

Between August 20th and September 9, much of the eastern half of the US has been well below normal.

Since August 15, we've only had six days at/above 80 degrees. Five of those occurred before August 23rd. The last time we had six or less days at/above 80 degrees between August 15 and September 10 was in 1997!

When was the last time we had overall average temperatures this cool this time of year?  How about 43 years ago...1982!

Notice how quickly our temperature fell after August 15th.

On top of the cooler pattern, rainfall is also well below normal after a very wet spring and first half of summer.

A large portion of Ohio is in a slight/moderate drought. Interestingly, compare this late summer/early fall to 2024 and you can see drought similarities.

Most of the Ohio Valley is running more than 4 inches below normal since mid August.

What does all of this mean for the rest of fall and into winter 2025-26?  Details in the weeks ahead.

Is This Summer's High Humidity Unique?

It seems like we haven't had much of a break from the high humidity across northern Ohio. It turns out that this summer SO FAR is the most humid summer on record in northern Ohio!

Here is the list (thru July 19):

1. 2025
2. 1995
3. 1949
4. 1987
5. 1999
6. 1973
7. 1943
8. 2010
9. 1989
10. 2018

The month of June started off somewhat cool and pleasant. The first two weeks of June featured several short periods of higher humidity (dew points above 60) with sharp drop-offs each time. The second half of the month saw a huge jump in humidity with a long stretch with dew points close/slightly above 70 degrees. Since the first of July, the breaks (dew points under 60) have been few and far between.

Compare this year to last year over the same time period. We had many more breaks from the high humidity.

Why has it been so consistently humid vs last year? The 500 mB reanalysis sheds some light on this. Notice the position of the highs and lows last year in the first half of summer. Ridge off the east coast did help increase the humidity from time to time. The deeper trough in the northern US suppressed the northward movement of moisture with a more dominant NE flow aloft across the Ohio Valley.

This year is different. The high pressure ridges are a bit further north as is the northern US trough. Couple this with a weaker but persistent trough over the southern plains and you have a more dominant south/southwesterly flow across the central US and Ohio Valley.

The long range outlook heading into early August is for the higher humidity (green colors) to shift into the central US and away from the southern Great Lakes.

Have The Temperatures Since May 15 Really Been That Cool?

 

My cucumber plants are loving the frequent showers. Took a risk planting on May 7th this year. Thankfully, we survived some of the colder mid May nights.

Yet the bigger question remains. Have temperatures since mid May really been that "cool"?

Before we take a deep dive into years past, put the earlier spring weather especially April and early May aside.  April and most of May for that matter was governed by the stratospheric warming in the higher latitudes in mid March. A winter pattern that developed late in the season. We felt the effects in spring with above normal rainfall and cooler than normal temperatures. That will alter your perception significantly.      I wrote about this last month. LINK HERE. This major driver was fading by mid May. Since we are into the last half of June, looking back to mid May is more appropriate. All temperature maps and charts are from May 15 to June 15-17 and give the temperatures vs the 30 year averages.

First, the average temperatures for Cleveland vs normal since May 15. Obviously a big drop off this year yet pretty much in line with 2023!  Most of the last 20 years have featured warmer than normal late springs. 2025 overall has been more in line with the 1980s and early 1990s.

How about just the average HIGH TEMPERATURES? 

Obviously a big drop off this year. Again the last 20 years featured warmer than normal high temperatures in late spring.

Now the average LOW TEMPERATURES. 

2023 was cooler. The early 2000s and 2010s warmth definitively featured here similar to the above charts.

How about the number of days at/above 80 degrees?

This is where this year stands out. We've only had FIVE days at/above 80 since May 15th. Only three other years had less:  2003, 1997 and 1948.  

Another way of showing this is to look at the number of days UNDER 70:

2025 is more in line with the late springs of the 1990s and early 2000s.

The extremes are what we remember, not so much the averages!

Since we are comparing year to year, how about rainfall between May 15 and June 17th?

Plenty of years similar in recent memory.  Remember not to think about April and early May's rainfall. That was due to a completely different set of weather drivers. LINK HERE. 

A few things to note, we are only looking at ONE location (Cleveland) over a select 30 day period. This late spring has been very similar across the southern Great Lakes, Ohio Valley and the entire mid-west!

Average Temperatures VS Normal - May 15 to June 15

Rainfall rates are starting to slow especially across the Ohio Valley over the last 30 days.

Rainfall Rate VS Normal Since May 15th

The take home message is that this late spring has been "cooler" than in recent years here in northern Ohio AND much of the central US. While the rainfall is closer to normal since mid May, our average temperatures whether you look at the highs or the lows are more in line with what we would have experienced in the 1990s/early 200s during the same period. Even the number of days in the 50s and 60s since May 15 is similar to the 1990s. The fact that we've only had 5 days above 80 degrees since May 15 makes it seem that much cooler.  If it weren't for the Stratospheric Warming in mid March, more than likely our spring weather (April and May) would have been much different!

The pattern as outlined earlier this month is starting to switch to summer. Get ready!