DENVER — Well, September has arrived — summer goes by in a hurry, doesn't it? — and things start to change as we get into the fall.
Typically, September is one of the nicest months of the year in Colorado. Some of the highlights:
- Big snow storms don’t happen often, but high mountains often get snow in September.
- September brings an end to most of the thunderstorms in Colorado.
- Beautiful fall color returns for a few weeks!
Here’s a look at some of Colorado’s September records:
- Earliest snow: Sept. 3 (1961)
- Snowiest September: 1971 (17.2 inches)
- Driest September: 1944 (only a trace of rain)
- Wettest September: 2013 (5.61 inches at DIA, but several more in northern counties of Boulder and Larimer, which caused significant flooding)
Temperatures
It can still get hot in September, too. Back in 2020, we had a 101-degree day on Sept. 5 — the only triple-digit day we’ve ever had in September.
The coldest was 17 degrees on Sept. 29, 1985.
Average highs in Colorado this month are 85 degrees on the first of the month and 73 degrees by the end of the month, while average lows go from 55 degrees on the first to 44 degrees by Sept. 30.
RELATED: An early forecast for when Colorado will see peak fall color in 2022
Severe weather
We can still get thunderstorms, but they become more rare as the month goes on. The typical threats are heavy rain and lightning, and not much in the way of tornadoes or large hail.
Let it snow?
These are the top seven snowiest Septembers:
- 1971: 17.2 inches
- 1936: 16.5 inches
- 1959: 12.9 inches
- 1895: 11.4 inches
- 1985: 8.7 inches
- 1995: 7.4 inches
- 1908: 6.5 inches
Snow can happen generally late in the month, but we can get some big storms. Pro tip: You can measure the storm, and learn what thousands of weather watchers have reported as far as precipitation, by becoming a CoCoRaHs volunteer.
Looking ahead
It looks like we'll go into the third straight winter with La Niña conditions, meaning cooler ocean water in the equatorial Pacific. It tends to drive the jet stream in from the northwest and that tends to suppress the monsoon moisture we get farther south. It also tends to drive the storm systems that we have during the fall into the winter from the northwest to the southeast, which favors the northern and central mountains with snow — somewhat at the expense of the mountains over southwestern Colorado.
As August comes to a close, we can expect warmer than average and slightly drier than average conditions across much of the central and western United States. So, any moisture we get comes in handy. Recent rains have helped improve drought conditions in much of the area along and just west of Interstate 25, while most of the West is still dealing with severe drought.
We will, of course, hope for some September moisture as we are still in the fire season. Wildfires are influenced by wind, heat and dry conditions, and the 90-day outlook has warmer and drier than average conditions in store – not great news.
Related: From wildfires to water supply: The threats of western drought, and the climate change connection
This graph shows the trend of western wildfires in recent years:
