Tag Archives: weather station

Part 2: Data shows Denver weather records skewed by move to DIA

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 2: Data shows Denver weather records skewed by move to DIA
Originally published March 3, 2009, Examiner.

Did you hear February was Denver’s least snowiest month?  Or was it?  As we discussed yesterday, a growing chorus of voices are objecting to the National Weather Service’s use of measurements at Denver International Airport for official Denver weather record keeping.  They claim that comparing data from DIA to previous records compiled for more than 40 years at Stapleton and more than 75 years before that in downtown isn’t a fair analysis.

In this second of a three part series, we take a look at some of the data to see just how big of a difference the 12 mile move from Stapleton to DIA made.  We also investigate potential issues with accuracy at the automated monitoring station at DIA that could forever be altering our climate records.  Tomorrow we will take a look at why all of this matters and why you should care.

Temperatures

An analysis shows that in just the last eight years DIA registers warmer high temperatures and cooler low temperatures than stations closer to downtown and in areas where people actually live.  For our comparison, we compared the last eight years of data for Denver International Airport versus the measurements taken at Buckley Air Force Base.  We chose Buckley because that is the closest official measuring station to the location of the old Stapleton International Airport.

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As you can see, the differences between where measurements have been taken for the last 14 years at DIA and where they were taken previously is significant.  DIA’s highest recorded temperatures each year averages nearly 2 degrees more than those closer to Denver.  Similarly, the station’s low temperatures are more than 2 degrees cooler.  This essentially throws any record high or record low temperatures that were recorded in the last 14 years out the window.  Any comparison of today’s data with historical records taken at Stapleton are invalid because the location move to DIA has clearly impacted the measurements.

Precipitation

This is probably the single most astonishing statistic and helps to show just how much of a difference 12 miles can make.  The National Weather Service has been taking precipitation measurements at both DIA and at the former Stapleton site so we can do a direct comparison between the two sites.  The results are astonishing.

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The chart clearly shows that precipitation measurements at DIA consistently underperform as compared to those at Stapleton.  Over the 8 year period, DIA on average measures 13% less precipitation than Stapleton.

One year in particular stands out.  In 2002 Colorado was in a drought by any measurement.  At the end of the year the National Weather Service proclaimed it as Denver’s driest on record.  However, that claim was based on measurements at DIA.  If you use the measurements at Stapleton – where weather records were kept for more than 40 years – the claim doesn’t stand up to scrutiny.  Stapleton’s 8.49 inches of precipitation in 2002, while certainly a dry, below normal year, would actually make it only the 6th driest year.  It can easily be argued that the claim that 2002 was Denver’s driest year should be discarded.

As a more recent example, March 2008 was proclaimed the “third driest March on record” when a mere 0.17 inch of precipitation was recorded at DIA.  However, 0.55 inch was recorded at Stapleton, an amount which would not put the month anywhere near the top 10 driest.

Snowfall

Historical snowfall measurement comparisons between the two locations unfortunately cannot be directly performed as it was only this year that the National Weather Service began measuring snow at DIA.  However, we can infer from the precipitation measurements noted above that there will be a comparable discrepancy in snowfall measurements as well.  This stands to reason as the plains receive less snow than areas closer to the mountains and going 12 miles east can make a big difference.

Issues of accuracy?

The precipitation and snowfall issue gets even further convoluted this year with the move to measuring snowfall at DIA.  While this would seem to solve the problem of inconsistency between taking precipitation measurements at DIA but snowfall at Stapleton, it turns out things aren’t quite that easy.

Weather enthusiasts have noticed problems with recent snowfall and precipitation measurements.  Just recently on Monday, January 12th, when a small snow storm moved through the Front Range the National Weather Service recorded 3 inches of snowfall but only 0.03 inch precipitation.

On average snow has a 10:1 moisture content which means that 1 inch of snow equals 0.1 inch of moisture.  Using the standard, approximately 0.3 inch precipitation should have been recorded – 10 times what was actually reported.

Extending the observation period out to include the two month period from December 1, 2008 to January 31, 2009, similar problems have occurred.  At Stapleton, where measurements are taken manually, 12 inches of snowfall was recorded with a moisture content of 1.08 inches – approximately an 11:1 ratio and one that could be expected.  By contrast, DIA – using automated precipitation measurements – recorded 15 inches of snow but a meager 0.37 inch of precipitation.  That is an unfeasibly dry 40:1 snow to precipitation ratio.

Detractors abhor the use of automated stations for such important climate records and are quick to point out that this is but one of many examples of inconsistent measurements.  One former NWS employee said, “the NWS sold their soul to automation years ago” and as a result we are stuck with inaccurate records.

Two airports, two different climates. Read the series:

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: