The fallacy of Denver's heat records

[PTPatrick]

Ok im ranting about this again...Many a headline has been made the month and in June about Denver's heat records....and make no mistake it has been hot. But once again it appears that DIA's location so far from where Denver used to measure its weather, Stapleton, is skewing the records. In 1995 they moved the measuring site. Our records for Denver go back to 1872...yes some previous sites were closer in even than Stapleton. Since 1872 Denver has officially had 75, 100 degree days.....35 of them have been since 1995... So almost half of our 100 degree days in the past 140 years have occurred in the last 17. I find that odd. Yeah climate change is real, yeah it's happening, but in Denver's case there are clearly some data issues. Looking at other recording sites around the metro reveals some didn't reach 100 yet this month, and only recorded a couple hundred degree days in June...DIA has had so far 12 counting for June in July. Records are still being taken at Stapleton but they aren't official. I don't understand why they had to move the official recording sites...now we're just comparing apples to oranges. the same holds true for snow and precip records...Denver's numbers have been steadily dropping since DIA became the official site. So it's, hotter in the day, colder at night, and drier at DIA. Rant over

[PTPatrick]

FOund more info... when comparing the denver UFCD records which are what's being recorded at Stapleton now, we haven't reached 100 yet in July, and the 100 degree streak in June was 4 days not 5, and the record for June was 103not 105 as measured in DIA. At Stapleton we've had 5- 100 degree days this year, at DIA we've had 12.

[tolakram]

Map view: https://maps.google.com/maps?saddr=Stap ... ra=ls&z=11

Is the location above correct?

Seems like a very short distance to me. Perhaps Instrument sighting is better or worse than before? Stapleton is surrounded by more greenery.

[brunota2003]

Seems to me to be a classic heat island effect (at least the warmer part). DIA is way more concrete and asphalt than Stapleton, just looking at the map above.

[PTPatrick]

Well, Stapleton was concrete and asphalt before...it's all been dug up and replaced by housing development. Stapleton was the previous airport. It should be opposite of urban heat island. DIA is basically in the boonies. But it's not. Denver is heavily effected by microclimates. I think DIA is more of a plains/valley microclimate. Most of Denver that people actually live in is more of a foothill valley Adjacent(I made that up) microclimate. Actually on non-extreme days, the differences appear less pronounced...but on the coldest days DIA is colder, and the hottest days DIA is much hotter.

I guess I don't have an issue with moving, but I do have and issue with trying to make meaningful comparisons between them, and proclaims record after broken record...when you really just broke the record player.

[PTPatrick]

"Map view: https://maps.google.com/maps?saddr=Stap ... ra=ls&z=11

Is the location above correct?

Seems like a very short distance to me. Perhaps Instrument sighting is better or worse than before? Stapleton is surrounded by more greenery."

I didnt really fully read that question. Yeah your locations are gorrect. Its 20+ miles from Downtown Denver to DIA. There are no less than 4 other "official" recording stations half as far miles...Buckly AFB, Stapleton UFCD, City Park station, and even Centennial apt is closer. 20 miles in the flat plains and midwest is nothing when it comes to weather observation. You have urban heat islands, but outside of that variation is small mile per mile compared to here being so close to the mountains. Basically, while Denver itself is relatively flat and the elevation is very close to that of DIA, downtown is closer to the mountains, and that does effect it, like being 20 miles from the ocean vs on the beach. Its like we are more protected from extremes.

One interesting thing about DIA is that its almost built into a slight ditch. You can appreciate this as you drive toward it and over the final hill before the terminal...that might have an effect. I think in theory the weather service, because this was such as sparcely population area before didnt really understand how different it was. And the elevation change was insignificant, so thought that moving sites would not change things much. To be fair, once you get inside the 470 loop elevation plays a much greater roll in weather. I think this was a learning experience for them as well. I guess we'll have to wait 50 years or so for the numbers to even out, and the records stop falling so frequently.

[tolakram]

Well, Stapleton was concrete and asphalt before...it's all been dug up and replaced by housing development.

Wouldn't this mean that the current measurements out of Stapleton would be too cool (or cooler than before)?

IMO, when it comes right down to it, individual site temperature records don't have that much meaning, even if they didn't move. Surrounding land use being the most likely culprit of modified readings. Here in Cincinnati the official readings are taken at CVG, the Northern Kentucky International airport. The temp at the airport can be significantly different from downtown, or in the suburbs. The airport was surrounded by farmland and forest, but now suburbs. In the last year the DHL expansion has added literally acres of concrete, which is also adding to heat island effect.

So even without changing locations the "records" can be suspect. Just in my opinion, of course. I don't spend a lot of time thinking about it.

[PTPatrick]

You bring up a good point. I certainly dont lose sleep over these things. I just find it interesting as a science minded person. Recording sites do change. Development happens...and that will continue to skew many cities data to some degree in the coming years. You mentioned that Stapleton might be reading too cool. I doubt thats the case. It is still a young neighborhood, with very small trees, and densley packed housing, its still a "congrete jungle" just one without a big terminal in the middle. I suspect the biggest difference besides proximity to the mountains is that vegitation has an effect on temps and the area around DIA is pretty much prairie grass, which does little to hold down temps like the urban forrest of central Denver. I think the bigger point is that now with 15 years worth of data from DIA, we have discovered that this was not a slight change. Its more drastic than any city has seen with urban development. To be sure, Denver has an urban heat island...one that effects Stapleton much more so than DIA. That to me is all the more reason that their recording is so skewed...if Stapeton's numbers arent as impressive and it lies within the urban heat island, that says a lot. I have read somewhere that urban sprawl toward airports that 50 years ago were on the edge of cities has lead at least a little to the increase in record high temps in the past 20 years or so...Denver, with its picking up and moving its airport 20 miles into farmland "should" have seen a drop in such records.

There are a handful of cities with drastic weather changes from one side to another...mosty cities along bodies of water for instance...and I know of none where offical recording sites have been moved from the waterfront to the inland areas. Moving our recording site that far away is more akin to say moving San Fran's to Oakland or San Jose, or moving Seattle's to Tacoma. The NWS seems to have assumed it would be like moving from Dallas to Fort Worth or from St. Paul to Minneapolis. Like I said, I guess its fine, but if the NWS is composed of scientists, I would think it would annoy them as much as it does me.

[Scott Patterson]

It is true that the weather station in Denver has moved, but when you look at the rest of Colorado and the stations that haven't moved, the heat has been impressive.

Where I live (Craig Colorado), at the Craig Moffat Airport (which station has not moved), we set the all time monthly records in January, March, April (tied), June, and July (tied), an impressive 4 out of 7 months. No other year holds more than one monthly record although 1990 held two before we broke one of them this year.

We are probably pretty unique in the 4 out of 7 all time monthly records though. This is partially due to the fact that we're sitting in the middle of a pocket of extreme drought. Because spring and early summer had almost no rain or snow (18% of normal) and almost completely cloudless, the humidities have been so low (5-9% before the past few weeks which have been wetter-finally) that the temperatures were able to climb to record levels while still rapidly cooling at night. We had an incredible 14 record highs in June, but interestingly our number of frost days was above normal (we went from frost to 90's on some days). We average two 90 degree days in June (we are at 6300 feet elevation and aren't as hot as most areas), but this year we had a record 15 (also, check out the dryness and that the nights were actually pretty cool when it hit 90, we are used to wide swings in temps, but with the dryness we had even more swings than normal):



Still even with some cool night during the dry spells, this year has been extremely warm in all months so far.

Before this year, Colorado Springs has hit 100 degrees four times. Jun 23 1954, June 24 1954, July 13 1954 and Jul 24 2003. Colorado Springs hit 100 or higher three times in June 2012 as well as breaking their all time record. 43% of all 100 (or higher) temperatures in Colorado Spings were in June 2012. The station there has only been moved slightly since being operational and hasn't moved at all for several decades.

Regardless of DIA readings, the heat in 2012 was impressive all over Colorado.

[PTPatrick]

Scott, definately did not mean to downplay the heat altogether...June was impressive to say the least even here in Denver, and certainly Colorado Springs's record days are testimate to that. Centennial Airport in the Denver metro also reached 100 twice in June, which I believe were records...Centennial is much higher than Denver, close to 5800 feet so thats dang hot. I roasted in Aspen in June with temps around 90. But looking only at the Stapleton site vs DIA puts all the Denver records into a little better perspective. DIA hit 100 3 times in the past week...stapleton hasnt hit 100 any of those days. Stapleton's 4 100 degree days in June, and 5 total for the summer is still EXTREME on its own, not counting the extra 7 of them DIA has recorded...and even more extreme if you compare it only to times prior to 1995.

All I know is I am ready for Autumn now. This heat is for the birds...

[PTPatrick]

I dont know if its global warming or the move to DIA but its definately warmer in Denver...
June 2012: Hottest on record in Denver
July 2012: Hottest on Record in Denver, hottest month ever in Denver
August 2011: Hottest on record in Denver

100 degree days in Denver so far in 2012: 12...that doesnt just break the record it blows it out of the water...previous was 7 days back in 2005

2000, 2001, 2003, 2005, 2008, and now 2012....all rank among top 10 warmest July's since 1872

Interestingly, the June and August "top 10 warmest" arent turning over nearly as frequently as the July records. I think this must have something more to do with the move. As I mentioned earlier, the temp gardient between Denver and DIA is seemingly smaller in transition season. In july the clouds build over the city earlier in the day than DIA, not to mention the monsoon moisture of July hangs closer to the the city/Mountains. I suspect that is why you are seeing warmest top 10 warmest July records falling more frequently.

[Scott Patterson]

Over on the other side of the Continental Divide we failed to make the hottest month. We missed it by 0.1 degrees, placing July 2012 as a close second hottest month ever. June 2012 was still the hottest June ever.

If it weren't for some rains cooling things off, we certainly would have made the hottest month. Luckily July 2012 actually had above normal rainfall for us. Average is 1.16 and we had 1.26. It has been the wettest month by far since November 2011.

We're still way below normal for the year. We're at 31% precipitation for the year and are still by far the driest year to date so far.

[MGC]

This is happening all over the country. Sites keep getting moved or new ones established. Take New Orleans for example. Record keeping began in the 1870's at Audubon Park. In the late 40's the new airport became the official site. Many times the max record will be broken at the airport but not at the park. You tell me, which site has a greater chance of breaking a record? One with a 140 years of observations or one with 60?.......MGC

[vbhoutex]

Same type of thing happened in Houston. The old station was at Hobby Airport on the South side of Houston nearer to the water. When Intercontinental Airport opened in 1969 on the far North side of Houston they moved the station out there. At that time it was in the boonies and cold records kept falling, but heat records didn't. Now it is surrounded by development and has added 3 new runways and several new terminals and other infrastructure and buildings. As this has happened the heat records have now started to fall over the last several years. In metro urban areas it appears to me that there isn't a good place to put the official stations unless they leave them where they were which makes sense to me since that is where the majority of the records have been taken in the first place. Moving them to get them to a place where there isn't anything around to influence them just doesn't make sense if you are trying to keep accurate records of a cities weather.