Coldest Start to December in Northern Ohio in Years. Does It Continue?

Per the long range outlook issued back on November 11, the cold arrived around Thanksgiving weekend and has not looked back. 

Temperatures for the first 3 days of December have been well below normal across much of the US. 

The FOX 8 forecast continues to show well below normal temperatures.

The main drivers of the colder pattern are:  A favorable tropical Pacific (MJO in phase 7-8) and a bit of upper atmospheric warming over the North Pole.

The first 15 days of December look to stay below normal across northern Ohio for the first time since 2005!  It's only happened two other times in the last century.

Its not just here in Ohio. Most of the country has had well below normal temperatures since Thanksgiving week.

Here are a few years that were similar to the current cold:  Temperatures vs normal on the left.  Upper level pattern on the right.  Notice how widespread the cold was in each instance along with persistent low pressure around the Great Lakes/eastern US.

2010

2005

1989

1958

Interestingly, the cold during the first half of December has been continuous but it hasn't originated from over the North Pole.  High pressure near Alaska has developed from time to time over the last week which has kept the central US trough/active pattern with frequent precip/snow.  But it's strength has been fluctuating. The low over Hudson Bay is trapped in between the Alaskan high pressure ridge and the low over Greenland. Definitely no sustainable blocking pattern capable of tapping arctic air.

What has to happen for the colder pattern to become extremely cold?

The Greenland low needs to transition to a high pressure block along with a sustainable Alaskan block.  That hasn't happened...yet.

Recently, a huge drop in the SOI (southern oscillation index) occurred. This indicates huge pressure pattern changes between Australia and Tahiti in response to the tropical changes (MJO moving into phase 8)

Notice on the long range outlook into the second half of December.  BOTH blocks seem to develop:

WATCH FOR CONSISTENT HIGH PRESSURE OVER ALASKA

WATCH DEVELOPMENT OF HIGH PRESSURE OVER GREENLAND

WATCH LOW DEVELOP CENTRAL US/HUDSON BAY

Here is the take home forecast message:

*  Cold continues but nothing extreme for southern Great Lakes through mid-December.

*  Active storm track continues with frequent snows across the central US/Great Lakes.

*  Short-lived break around December 16-18

*  Then cold reloads as blocking pattern establishes itself last 10 days of December/early January

Watch how the cold continues, a small break mid-month before the cold build around Alaska which heads south around the 20th.  Get ready for a Arctic Christmas!

First Snow Last Week. How About Thanksgiving Forecast and Beyond?

The first snow of the season occurred last week then quickly melted. 

How about Thanksgiving?  Back on November 11, I sent this text out to our weather department:

"...MJO is increasing in amplitude into phase 6,7 and 8. Pressure between Darwin station and Northern Australia (SOI) has just taken a significant drop a few days ago. Both of these strongly suggest that we will have a pretty significant warm-up the week of Thanksgiving...probably a few days well up into the '60s. Middle of the country could see some severe weather. Deep trough develops Central us and eventually migrates East. Potentially cold enough for some snow this Saturday and Sunday after Thanksgiving but more so the first week and a half of December. That should feature below normal temperatures, a couple of clipper systems and multiple rounds of lake effect."

SOI analog during a neutral ENSO shows the trough on day 22 after the drop.

SOI analog during La Nina snows a weak ridge with flanking trough on day 21 following SOI drop.

This is the graphic I started showing on November 12 for the week of Thanksgiving/first week of December and continued to show this week (Nov 17th).

All of this analysis was done outside long before the long range models had Thanksgiving and beyond in their solutions. 

Now, on November 17, the long range models are showing the huge west-to-east temperature difference Thanksgiving week:

Notice how the warmth doesn't last long.  Notice the ridge over Alaska (red) and the following trough (blue) in the central US.

Temperature forecast from the Wednesday before Thanksgiving through November 30th.

Do I think this colder pattern early December last long?  Its looking more transient with some moderation around mid-month. Eventually the colder pattern will re-establish itself longer term after the New Year!

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.