Category Archives: Climatology

Climatology, Thornton Weather

Meteorologist: DIA weather recording alters our temp records

Record or not? Why Denver's climate records should have an asterisk next to them. (ThorntonWeather.com)
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:

Climatology, Thornton Weather

Denver ties record high temperature for August 17

Record High Temperature

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.

Climatology, Colorado Weather, Thornton Weather

NOAA’s fall outlook predicts warmer and drier than normal conditions for Colorado

NOAA CPC Fall 2024 Temperature Outlook (NOAA)
NOAA CPC Fall 2024 Temperature Outlook (NOAA)

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)
NOAA CPC Fall 2024 Precipitation Outlook (NOAA)Seasonal
Climatology, Thornton Weather

Part 1: Do Denver weather and climate records have an asterisk attached?

Two airports, two different climates. How Denver's weather and climate records are skewed by a 12 mile move. (ThorntonWeather.com)
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.

Map:

http://maps.google.com/maps/ms?ie=UTF8&hl=en&msa=0&ll=39.819612,-104.886475&spn=0.337528,0.594635&z=11&msid=118280686911175493835.0004640da10c79cdcdba0

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:

Climatology, Thornton Weather

July 2024 weather recap: Another warm one, precip comes in close to average

Thornton, Colorado's July 2024 temperature summary. (ThorntonWeather.com)
Thornton, Colorado’s July 2024 temperature summary. (ThorntonWeather.com)

Certainly, in our minds, July 2024 was a very warm one as it seemed like the 90+ degree days just kept on coming. Average temperatures did come in a good bit above normal. Precipitation wasn’t anything extraordinary and while it ended up close to average, the last half of the month was quite dry.

High pressure was the dominating force for the majority of the month with only intermittent breakdowns of the ridge. As a result, overall hot and dry conditions were the general rule. There were, however, just enough effects from some cold fronts to keep average temperatures relatively in check.

The last 10 days saw only one day with precipitation leading to dry conditions across the Colorado Front Range. This resulted in numerous wildfires in the foothills and smoke blanketing the area for several days.

Thornton’s average temperature for the month was 74.9 degrees. This was a good bit warmer than our running 18-year average for the month of 73.8 degrees. This made July 2024 the sixth warmest July over that period. Temperatures ranged from a maximum of 102 degrees on July 12th down to a low of 50.7 the morning of the 4th.

The Mile High City, as measured at Denver International Airport, came in a good bit warmer with an average mercury reading of 75.7 degrees. This was just a bit above Denver’s long term July average of 75.1 degrees. Denver set record highs on the 12th and 14th (102 and 101 degrees respectively) and tied the record high of 99 degrees on the 29th.

In terms of precipitation, Thornton received 1.74 inches during the month. Nearly half of that coming over two days on the 20th and 21st (0.80”). The total fell short of our running average for the month of 1.95 inches.

Denver’s official rainfall total for the month came in at 1.10 inches. This was well below the city’s July average of 2.14 inches.

Click here to view Thornton’s complete July 2024 climate summary report.

Thornton, Colorado's July 2024 precipitation summary. (ThorntonWeather.com)
Thornton, Colorado’s July 2024 precipitation summary. (ThorntonWeather.com)
Climatology, Thornton Weather

Thornton’s August 2024 preview: Temps begin to cool, severe weather eases

Thornton's August Weather Preview
Thornton’s August Weather Preview

As summer vacations wind down and families prepare to send their kids back to school in August, Colorado weather also starts to settle down. The chances for severe weather decrease markedly during August and by the end of the month daytime temperatures are dropping quite a bit as well.

Find out more about what lies ahead with Thornton’s August weather here.