Thornton was finally able to break out of the hot, dry weather pattern of recent months and see things get a bit more normal. September historically is one of our most pleasant months and 2025 largely held true to that.
We did start out pretty mild and precipitation was meager for the first half of the month. Finally, on the 13th, we began to see things cool down and then on the 16th got a nice shot of rain (0.61”).
The rest of the month offered mild but comfortable temperatures. A strong trough on the 23rd cooled us considerably with that day offering high temperatures nearly 20 degrees below normal. It also brought a very healthy shot of rain (1.21″).
In the end, the average temperature for the month of September ended up very close to average. Thornton’s average for the month was 64.6 degrees. This was just a hair higher than our 19 year running average for the month of 64.3 degrees. Our maximum temperature for the month was 92 degrees and came on the 10th. Our coolest reading of 42.3 degrees was on the 25th.
For Denver, at Denver International Airport where the Mile High City’s official measurements are taken, temperatures were on par with ours. They reported an average for the month of 64.7 degrees. This was close to their long term average for September of 64.8 degrees.
In terms of precipitation, Thornton saw a notable 2.09 inches for the month. This was far above our 19-year running average of 1.51 inches for September. This was the fourth wettest September over that period.
The Mile High City was quite a bit drier with 1.35 inches recorded in their rain bucket. It was, however, above their long term average for the month of 1.09 inches.
No snow was recorded in Thornton or Denver for the month.
Click here to view Thornton’s complete September 2025 climate summary report.
