Hottest September on record for the Twin Cities?

With just a couple days to go, September could finish as the hottest on record for the Twin Cities. This year’s warmth was made much more likely due to climate change.

Summer heat drove hot September

While it appears we’ve hopefully broken our months long dry stretch, the well above-normal temperatures continue, for now.

The average temperature for the month of September so far in the Twin Cities sits at 68.8 degrees through Sept. 28. If that holds, this ties the hottest September ever recorded, tying the No. 1 spot that stood for 126 years.

Statewide, it is the hottest September on record, according to longtime climatologist and meteorologist Mark Seeley.

If we plug in forecast numbers for the final few days of the month we come up with an average that will likely go up to around 69 degrees thanks to this next blast of heat.

Let’s say, hypothetically, the actual highs and lows through Saturday end up 5 degrees cooler (which is unlikely), we still end the month at 68.8 degrees, tied with No. 1 hottest out of 150 years. 

Across the state, the story is similar. While the Twin Cities is 4.7 degrees above normal, St. Cloud sits at 5.3 degrees above normal, Duluth at 4.1 degrees, International Falls at 4.6 degrees, and Marshall at 4.3 degrees warmer than normal.

These are huge anomalies considering that the standard deviation for September average temperature is just about 3 degrees.

Climate change fingerprints

It’s pretty hard to imagine a month like this one playing out without the impact of human-caused climate change.

Over the past 50 years, average September temperatures have warmed several degrees. In fact, analyzing it statistically, a September average temperature of 69 degrees is made at least five times more likely with our warming of several degrees in recent decades.

While highs in the 80s certainly happen at the end of September and early October and have since records began, they’re becoming more prevalent and made more likely when the average temperature this time of year has increased so much.

Let’s take a look at Friday’s forecast high of 70s and 80s across southern Minnesota. Climate Central’s Climate Shift Index shows that it’s made twice as likely as a result of warming trends.

Of course, this weekend wasn’t the only heat wave we saw this month. The month started with record-breaking heat and the longest such heat wave, that late in the season ever recorded.

High temperatures on Sept. 3 were made 2 to as much as 5 times more likely (in northern Minnesota) due to climate change.

As we begin October, Sunday’s forecast high temperature in the mid-80s for example, is nearly 20 degrees above normal. That warmth looks to continue through Tuesday before we finally see a more familiar fall chill set in.