Thornton, Colorado’s September 2024 temperature summary. (ThorntonWeather.com)
Mother Nature can be so fickle. While September brings the start of autumn, she was intent on keeping summer rolling along and in doing so, delivered mercury readings well above normal.
The month was a calm one, lacking much of any kind of drama beyond the temperatures. We started out very warm and dry for the first three days then, finally, a little bit of relief arrived. Temperatures cooled a bit and we received a nice shot of rain on the 4th and 5th.
For the next two weeks, dry conditions dominated with no precipitation. Over the period temperatures remained well above normal.
Finally, on the 21st, we saw some relief and temperatures on the 21st and 22nd were only in the 60s. We also received a welcome shot of rain totaling 0.81 inches.
Temperatures rebounded on the 23RD and dry weather continued through the end of the month.
In the end, Thornton saw an average temperature for September 2024 of 67.9 degrees. This was far above the running 17-year average for the month of 64.2. In fact, it was Thornton’s warmest September over the period. Temperatures in Thornton ranged from a high of 93.1 degrees on the 3rd down to a low of 42.7 degrees on the 23rd.
For Denver, as measured at Denver International Airport, the month was a good bit warmer recording an average of 70.0 degrees. This too was far above the month’s average of 64.8 degrees. Further, it put September 2024 into the books as the Mile High City’s warmest September on record.
Thornton really only saw two rain events but both were pretty decent ones, dropping 1.26 inches into the rain bucket for the month. That was a bit below our September average of 1.48 inches.
Denver recorded very similar numbers with 1.24 inches of precipitation. This was just shy of the Mile High City’s September average of 1.35 inches.
Neither Thornton nor Denver recorded any snow during September 2024.
With the first full month of fall here, October usually brings one of the quietest weather months in the Denver area with plenty of mild, sunny days and clear, cool nights.
October is historically the second sunniest month and conditions are generally calm.
However we also will usually see our first taste of winter during the month with the first freeze and first snowfall of the season. Temperatures as well will start to drop and by the end of the month the average nighttime lows are below freezing.
It may be the end of September, but Mother Nature is intent on keeping the summer heat coming.
As measured at Denver International Airport, Denver hit a high temperature today of 92 degrees. This ties the record high for September 29 last set in 1892.
The Mile High City also tied the record for the warmest low temperature for the date. The mercury only descended to 61 degrees, tying the record mark last set in 1981.
Here in Thornton, we matched DIA with a high of 92 degrees. We were, however, a good bit cooler with a low of 55 degrees. At Stapleton, where historical Denver weather records were taken from 1950 to 1995, the high was 90 degrees and the low 56 degrees.
As measured at Denver International Airport, the Mile High City hit an official high temperature of 93 degrees today. That easily breaks the old record high for September 26 of 90 degrees set way back in 1892.
Here in Thornton, we were a bit cooler with a high of 91 degrees recorded. At Stapleton, where historical Denver weather records were taken from 1950 to 1995, the high was 90 degrees.
We entered the month on a three-month streak of warmer, drier than normal conditions. The hope was that August would bring some relief but it did not.
The first week of the month saw mercury readings all above the 90 degree mark. We did, however, record some minor precipitation during that period. Three days of below normal mercury readings gave us some hope but that was short-lived.
The final three weeks of the month saw temperatures routinely above average with only a few exceptions. We did see a few days with decent precipitation but those were uncommon as compared to most other days which remained dry.
Thornton’s average temperature for August 2024 came in at 73.5 degrees. This was nearly two degrees above our 18-year running average for the month of 71.8 degrees. Our warmest reading of 99 degrees came on two days, the 2nd and the 17th. The second to last day of the month, the 30th, saw our coolest reading of the month at 52 degrees.
By comparison, Denver continued to show its warm bias. As measured at Denver International Airport, the Mile High City’s average temperature for the month came in at 75.6 degrees. That is well above their long term average of 72.9 degrees and puts the year into the books as the 5th warmest August on record for Denver. During August 2024, the city recorded a maximum of 102 degrees on the 4th and a low of 50 degrees on the 30th.
The National Weather Service noted that summer 2024 (June, July, August) will go into the history books as the second warmest summer on record (since 1872). It, of course, bears repeating that since the service moved Denver’s official station to DIA in 1984, records are severely skewed and not particularly comparable to those taken at the previous official stations.
In terms of precipitation, the month did end up drier than normal but, thankfully, not by a lot. Thornton recorded 1.07 inches in our rain bucket. This was below the 18-year average of 1.24 inches for the month.
Out at the airport, it was a bit drier with 0.92 inches being recorded for Denver. That is well below their August average of 1.58 inches.
Following an August that was unseasonably warm, we find ourselves heading into September hoping for relief. The month can bring plenty of rain and even our first snow of the season but more often than not, it is one of the most pleasant along the Colorado Front Range.
As temperatures start to drop, September usually reminds us that summer is at an end and fall is now here. Sunshine is predominant though as the month actually has the highest percentage of sun out of any month. Sunny days and clear, cool nights are the standard weather pattern for the month.
The month can bring extremes however. We will of course forever remember 2013’s devastating floods brought on by record-setting rain. Longtime residents might remember September 1971 which brought over 17 inches of snowfall.
Record or not? Why Denver’s climate records should have an asterisk next to them. (ThorntonWeather.com)
In 1995 with the opening of Denver International Airport, the National Weather Service moved the Mile High City’s official weather station to the new facility. This location, 12 miles from the old Stapleton site, oftentimes sees far different weather than what the majority of people in the Denver area see and it is reflected in our weather records.
We have long said that any claims of a weather record having been set since 1995 should include an asterisk, noting that the comparison is to the old locations and thus not really valid. Those 12 miles make a world of difference.
In the latest example of how our climate records are being altered, Denver supposedly set five all-time record high temperatures this summer. The reality? Not one of those days would have been record-setting had the station not been moved.
Retired National Weather Service meteorologist Dave Larison has long railed against the move of the weather station. In a recent letter to the editor in the Denver Post, he called out the media hype and the National Weather Service for the invalid comparisons. It is shared here with his permission.
Denver’s recent heat wave wasn’t really record-breaking and here’s why
Denver Post Opinion, August 21, 2024
Re: “100-degree sizzlers here to stay as summers get hotter,” Aug. 11 news story
Any discussion of Denver weather records must include the fact that the official recording site was moved to Denver International Airport (DIA) when it opened in 1995. This location has a different microclimate than the previous site of Stapleton Airport, situated 12 miles to the southwest of DIA. Before Stapleton, weather records were taken in downtown Denver dating back to 1872.
On Sunday, Aug. 4, the daily record high of 102 set at DIA would not have been a record at Denver Central Park (Stapleton) where the daily high was 96. In fact, none of the five daily record highs set at DIA this summer would have been records at the previous Denver sites. DIA has reached 100 degrees on six days in 2024, while the highest temperature recorded at Central Park has been 99.
With all the media hype of human-made climate change and record heat, we need to be careful not to compare apples and oranges with weather stats going out to the world representing Denver. Average annual precipitation also tends to run a bit lower at DIA, and snowfall is quite often less at the airport due to its proximity farther away from the mountains.
— Dave Larison, Longmont
— Editor’s note: Larison is a retired National Weather Service meteorologist
RELATED: Two airports, two different climates. Read the series:
Another high temperature record is in the books for the Mile High City. As measured at Denver International Airport, Denver hit a high temperature of 98 degrees. This ties the record high for August 17 last set in 2020.
Here in Thornton, we were actually warmer with a high of 99 degrees. At Stapleton, where historical Denver weather records were taken from 1950 to 1995, the high was only 93 degrees.
Tired of the heat of summer? Well, don’t power off that air conditioner just yet.
NOAA’s Climate Prediction Center’s autumn outlook for September, October and November, if accurate, would have us continue the above normal, drier than normal conditions of recent months.
The forecast gives above normal chances for most of the contiguous United States to see above average temperatures. For Colorado, the Four Corners region has the greatest chance at a likeliness of 60 to 70 percent. Most of the state, including the Front Range, is at a 50 to 60% chance.
In terms of precipitation, a good chunk of the nation has good chances to see below normal levels. The vast majority of Colorado is being given a 40 to 50% probability of below normal levels.
NOAA CPC Fall 2024 Precipitation Outlook (NOAA)Seasonal
Two airports, two different climates. How Denver’s weather and climate records are skewed by a 12 mile move. (ThorntonWeather.com)
ThorntonWeather.com’s owner and operator used to write for a now-defunct website called Examiner. This was a national site but with locally focused content. As the Denver Weather Examiner, Tony covered a number of topics related to Denver and Colorado weather.
Among them, he was always quick to point out how Denver’s weather records were being skewed by the move of Denver’s official weather station to Denver International Airport. In 2009, he wrote a three-part series explaining why this was an issue and why it mattered.
Fifteen years later, this continues to be a problem and thus we are re-publishing the series here. While the data is not current and some of the images were lost with time, readers can still understand and appreciate the problem.
Part 1: Do Denver weather and climate records have an asterisk attached? Originally published March 2, 2009, Examiner.
February 2009 is Denver’s least snowiest February on record. A new record high temperature is recorded on January 21, 2009. Record low temperatures are recorded on December 14th and 15th of last year.
These announcements are common and we all take notice when we hear them and they make for great water cooler chat topics but are these claims accurate?
In 1995 Denver finally opened its new airport out on the plains east of the city. This new facility, 12 miles as the crow flies northeast of the old Stapleton International Airport, moved the airport from an urban environment to a rural one and more than 19 miles from the center of Denver. Following that move, the National Weather Service (NWS) began taking some of its official measurements at the glistening new airport. In doing so, some say Denver’s climate records have forever been altered and as such any weather record should have an asterisk attached to it.
Official Denver weather statistics were collected from the NWS’ downtown Denver office from November, 1871 to December 1949. In January 1950 observations were moved to Stapleton International Airport where they remained until February 1995. From March 1995 forward, Denver’s official weather has been measured at DIA. With the move, precipitation switched to Automated Surface Observing Systems (ASOS), an automated means of making the measurement. In a somewhat confusing twist, the measuring of snowfall remained at Stapleton until just this snow season.
The question many are asking – Does a move of 12 miles make that much of a difference when measuring the weather? Twelve miles is the same distance as between downtown and Golden, or downtown and Centennial or downtown and the northern edge of Thornton. How often do we hear about heavy snow falling at I-25 and C-470 and yet downtown remains dry? If you live in any of the outer metro area suburbs you know that what the news stations report as the weather downtown rarely is what you experience.
Twelve miles, particularly in a topographically and geographically diverse area as the Front Range would appear to make a world of difference. That is why when you watch the evening news local meteorologists include the conditions at their local station downtown in addition to the official data at DIA. Most local meteorologists have railed against the move and are quick to point out that the weather as measured at DIA does not reflect what Denver weather truly is.
When new records are announced, detractors point out that it isn’t fair to compare the data compiled at DIA with that which was recorded previously at Stapleton or downtown. Just yesterday the National Weather Service announced that February 2009 was the least snowiest on record. But was it really? The NWS says Denver received only a trace of snow (less than 0.1 inch) but this was at DIA. The vast majority of the metro area had at least some measurable snow during the month and Stapleton, where official records were kept for more than 40 years, had 0.8 inch of snow – a number that would push it well out of ‘least snowiest’ contention. Many say we are comparing apples and oranges.
Empirical data shows that every meaningful statistic has been skewed by the move to DIA. In this three part series we will take a look at how moving Denver’s official weather measurements to DIA have skewed Denver’s climate records and why it matters to you. Tomorrow we take a look at the empirical data showing just how big of a difference 12 miles makes. Wednesday we’ll tell you why it matters and learn about some possible solutions to the problem.
Stay tuned!
Two airports, two different climates. Read the series:
With the first full month of fall here, October usually brings one of the quietest weather months in the Denver area with plenty of mild, sunny days and clear, cool nights.
