It's Minnesota's warmest, driest September on record and it's not even close

This September is the warmest on record in the Twin Cities and statewide and it’s not even close. Typically, we measure the differences between the top or bottom months and seasons in tenths of degrees, but this September is likely to be warmer than the previous No. 1 spot by a full degree, which is huge.

Oh, and the previous No. 1 spot was September 2023....

It’s also going down as our driest September on record in the Twin Cities with just 0.06 inches of rain. Most of the state has seen a fraction of normal rainfall for the month, allowing drought and abnormally dry conditions to grip 80% of the state.

September is one of our fastest-warming months over the past several decades.

Average September temperatures have warmed 5 degrees in 50 years. While winter is warming faster in terms of absolute degrees of warming — specifically January average temperatures warming a staggering 7.5 deg F in 50 years — September is warming faster in terms of normalized or standardized values. A standardized value is obtained by taking the pace of warming divided by the standard deviation or variability. Winter has much more variability than September or summer, so this standardizing of values allows us to compare apples to apples versus apples to oranges.

The standard deviation in September average temperature is just 2.8 degrees farenheit, whereas in January it’s 6.5 degrees. So, on this scale, September warming is actually 1.5 times greater than January.

The warmest places, relative to normal, this September are in northern and northwest Minnesota, which will end up 6-7 degrees above normal.

Another fascinating element comparing this off-the-charts warm September to last year is the consistency in the warmth.

That’s how we beat last year. Last September started the month with 5 consecutive days in the 90s, peaking at a high of 98 degrees on Sept. 4. This September we haven’t hit 90, but it’s been consistently warmer, whereas last September, despite being the second warmest, did have the more typical ups and downs we should have as we begin the transition from summer to fall.

Besides temperature data, the winds tell the same story.

Look below at the comparison of September 2024's wind rose to a normal September (1991-2020 average). A wind rose displays the magnitude and direction of winds averaged through the month. You can see the stark contrast. A normal September (or any fall month) should have a typical tug of war between northwest and southeast winds as cooler and warmer air battle it out. This September has had winds dominated from south and southeastern directions.

The obvious question then comes about: How will this affect winter?

Well, September usually has little correlation to the winter pattern as a lot happens between now and then. The Arctic has just started to dive into darkness and cold air is just barely starting to develop. The Arctic sea ice minimum, after a long summer of melting, was reached probably on Sept. 11. It was the seventh lowest on record. But, look at just how warm the whole hemisphere is over the past 30 days...

With this much heat in the entire northern Hemisphere and low sea ice yet again, it can probably be safely concluded that, at least on a hemisphere-wide basis, winter will get a late start.

It will just simply take longer to cool things off. Longer range forecast models already hint at potential for a rather warm December.

I will be releasing my take on what I think winter 2024-2025 will bring in the next week or two, but all the talk of La Niña should be taken with a grain of salt. A weak La Niña may mean not much given the background of a hot planet and hot oceans.

BMTN Note: Weather events in isolation can't always be pinned on climate change, but the broader trend of increasingly severe weather and record-breaking extremes seen in Minnesota and across the globe can be attributed directly to the rapidly warming climate caused by human activity. The IPCC has warned that Earth is "firmly on track toward an unlivable world," and says greenhouse gas emissions must be halved by 2030 in order to limit warming to 1.5C, which would prevent the most catastrophic effects on humankind. You can read more here .