COLORADO (KOAA) — September has seen the largest amount of warming in the last 30 years in Colorado, of any month of the year Data from the National Oceanic and Atmospheric Administration show that the state, El Paso, and Pueblo counties have all warmed 2 degrees in September.
Between 1960 and 1990:
- Colorado averaged 57 degrees
- El Paso County averaged 58.6 degrees
- Pueblo County averaged 63.4 degrees
Between 1990 and 2020:
- Colorado averaged 59 degrees
- El Paso County averaged 60.6 degrees
- Pueblo County averaged 65.4 degrees
Of course, it does still cool down in September. And two degrees doesn't sound like a big change.
But what this shows up as is more 90 degree days that last later into the month: when the leaves change, when the growing season ends, and how often it snows.
It's also been drier - in the short term - in Colorado Springs compared to past years. Eight of the last 10 years in Colorado Springs have had below average rainfall in September.
Longer range trends show other dry periods - for example in the 1940s and 1950s. But it's still a significant change given how long below average rainfall trends have persisted.
The strongest changes are in our average last 90 degree days.
In Pueblo, over the last 130 years the average last 90 degree day has been on September 20th. But, between 1995-2024 specifically, that last date has been September 27th on average.
In Colorado Springs - the long term average is August 19th; the average between 1995-2024: September 1st.
In practice here's how that shakes out: the last year Colorado Springs lacked a 90 degree day in September was 2015.
The reason September is so significantly impacted is because it is historically a transition month.
The heat domes you've heard of in summer are becoming more common in September.
Those domes tend to set up over the Rockies, leading to extended periods of warmth that impact our state.
The net effect of a warmer and drier environment is mixed. It extends the growing season - which can be helpful for farmers. But, it increases wildfire risk and on average puts more strain on our water resources.
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