Deck Pic Posted September 15, 2015 Share Posted September 15, 2015 My only purpose here is to debunk the "bad sensor" myth. It's a be careful what you wish for situation...I don't doubt the sensor may have been a little off and in need of replacement...starting last year DCA seemed to be starting to run too warm compared to other stations. I had brought up to the CWG team about blending the stations for my outlook instead of using solely DCA for predictions and scoring...But UHI is real as you know and a sensor isn't going to change that...I've always cautioned that moving the station or changing the sensor might make minor improvements but it isn't going to alter the sometimes significant temp differences between DCA and outlying stations..... Link to comment Share on other sites More sharing options...
famartin Posted September 15, 2015 Share Posted September 15, 2015 My only purpose here is to debunk the "bad sensor" myth.A faulty purpose Link to comment Share on other sites More sharing options...
CAPE Posted September 15, 2015 Share Posted September 15, 2015 It's a be careful what you wish for situation...I don't doubt the sensor may have been a little off and in need of replacement...starting last year DCA seemed to be starting to run too warm compared to other stations. I had brought up to the CWG team about blending the stations for my outlook instead of using solely DCA for predictions and scoring...But UHI is real as you know and a sensor isn't going to change that...I've always cautioned that moving the station or changing the sensor might make minor improvements but it isn't going to alter the sometimes significant temp differences between DCA and outlying stations..... I am not really wishing for anything. Agreed on UHI. But if there is a mystery to be solved with the measurement equipment, then there has to be some methodology applied. Resistance-based sensors(assuming thats what it is, RTD or thermister) dont tend to be "a little off" as you put it. They follow a specific resistance vs. temp curve, which is modeled as linear, but obviously not perfectly so. But taking the shotgun approach(replacing the sensor when its functioning correctly) is not going to solve anything. Based on the tests that were performed, and the data that resulted(from the CWG article) the sensor was operating as specified. The only parameters that can realistically be tested on a sensor, are accuracy and repeatability. Those were tests of its accuracy. In order to perform that test, there must be a set of criteria, which there was. The allowable error for a given test is a function of the stated accuracy of both the sensor, and the test reference. No sensor is perfect, and in this case, using that psychrometer based unit to verify the sensor reading is somewhat of a limitation. Using a more accurate test device would allow for testing to a different tolerance, perhaps plus/minus 2.5 degrees F. The other part of the equation here is the electronics (measuring/indicating) to which the sensor is connected. This could introduce small errors in the measurement, and thus the temperature readings. And I completely agree with your last sentence. As I stated in a previous post, most likely any small errors (sensor related) are due to localized environmental effects. Link to comment Share on other sites More sharing options...
CAPE Posted September 15, 2015 Share Posted September 15, 2015 A faulty purpose I think you misunderstood. Or was that an attempt to be funny Link to comment Share on other sites More sharing options...
Ian Posted September 15, 2015 Share Posted September 15, 2015 We should just close this thread since we will never truly prove anything one way or another. Link to comment Share on other sites More sharing options...
CAPE Posted September 15, 2015 Share Posted September 15, 2015 We should just close this thread since we will never truly prove anything one way or another. Probably. Plus I know I have bored everyone with my esoteric technobabble. Link to comment Share on other sites More sharing options...
famartin Posted September 15, 2015 Share Posted September 15, 2015 I think you misunderstood. Or was that an attempt to be funny Was your post an attempt to be funny? If so, I apologize, I did misunderstand. If not... scientific investigators *shouldn't* have certain purposes (such as disproving something), as it tends to bias their interpretation of the results in that direction. I realize that rarely is that the case. We should just close this thread since we will never truly prove anything one way or another. Granted, though you could argue that about a lot of things. Link to comment Share on other sites More sharing options...
Deck Pic Posted September 15, 2015 Share Posted September 15, 2015 We should just close this thread since we will never truly prove anything one way or another. I need something to bump this winter when DCA has a low of 22 and IAD is 5 Link to comment Share on other sites More sharing options...
CAPE Posted September 15, 2015 Share Posted September 15, 2015 Was your post an attempt to be funny? If so, I apologize, I did misunderstand. If not... scientific investigators *shouldn't* have certain purposes (such as disproving something), as it tends to bias their interpretation of the results in that direction. I realize that rarely is that the case. Well I was just trying to provide some insight from a technical perspective. And based on what I know about the subject, and reading the CWG article outlining the tests and the results in some detail, its pretty clear to me the sensor was not faulty. So basically making the case to remove that from the list of possible sources of error. Link to comment Share on other sites More sharing options...
Ian Posted September 15, 2015 Share Posted September 15, 2015 Granted, though you could argue that about a lot of things.Sure but in the grand scheme this is a non issue. If it's fixed that's great. If it was broken that sucks. You are undoubtedly aware that databases are filled with problems all over. I'd wager a lot of the historical wx stats we all share and look into have considerabe uncertainty as to perfect accuracy. But in reality as long as its within some reasonable margin of error it's not a huge deal. I won't hate on anyone for continuing to search for the truth here.. Just noting it won't really change anything at this point. Link to comment Share on other sites More sharing options...
Ian Posted September 15, 2015 Share Posted September 15, 2015 I need something to bump this winter when DCA has a low of 22 and IAD is 5We need to get Dulles moved to a representative spot and move BWI back to the city. OR mesonets for everyone! Link to comment Share on other sites More sharing options...
CAPE Posted September 15, 2015 Share Posted September 15, 2015 Sure but in the grand scheme this is a non issue. If it's fixed that's great. If it was broken that sucks. You are undoubtedly aware that databases are filled with problems all over. I'd wager a lot of the historical wx stats we all share and look into have considerabe uncertainty as to perfect accuracy. But in reality as long as its within some reasonable margin of error it's not a huge deal. I won't hate on anyone for continuing to search for the truth here.. Just noting it won't really change anything at this point. Well stated. I made my case. I am out. Just dont anyone reply to my posts and pull me back in Link to comment Share on other sites More sharing options...
Ian Posted September 15, 2015 Share Posted September 15, 2015 Well stated. I made my case. I am out. Just dont anyone reply to my psots and pull me back in It is interesting. I wish there was a silver bullet answer. I just feel like we are running in circles at this point. Link to comment Share on other sites More sharing options...
WEATHER53 Posted September 15, 2015 Share Posted September 15, 2015 The daytime highs have been brought into proper alignment but there was so much push back on that that they have to take it gradually. Next up will be some form of relocation and/or a mitigation of immediate site radiance Link to comment Share on other sites More sharing options...
Inverted_Trough Posted September 16, 2015 Author Share Posted September 16, 2015 This is an awful post... sensors on steroids? hmm. Actually, its the fault of the sun god. And damn that god of wind too. This is all so mystical and magical. Let me rephrase then. The sensor was a piece of crap. You don't need to know the physics of the measuring device to determine this - you just need to know statistics. The difference between IAD and DCA highs have ranged from 0 to 2 degrees (as famartin's stats support). Suddenly we had 19 consecutive months where the difference in airport highs exceeded what was typically observed. The chance of this happening by simple random variation is statistically impossible. Either something significant changed in the surrounding environment at either IAD or DCA, or one of the sensors had a warm bias. Flash forward to five weeks ago. The sensor at DCA was replaced. Voila, immediately the difference between airports reverted to within its historical range (1.6 degrees thus far). The verdict: the sensor at DCA was a piece of crap. The difference between old sensor (~4 degree difference) and new sensor (1.6 degrees) is 2.4 degrees - that's a significant difference. That supports my assertion that the old sensor was reading 2-3 degrees too high. I'm aware of other possible contributing factors such as the nature of certain weather patterns, wet/dry soils, etc; but sometimes the simplest explanation is the best one: the sensor at DCA was crap. I don't know why there are so many DCA apologists here - even posting this topic immediately triggered pushback and nonstop chanting of "UHI" (which, by the way, was never something I argued about). I think there should at least be acknowledgement that there is strong evidence that the DCA highs in 2014 and most of this year were, to put it in football terms, inflated. Link to comment Share on other sites More sharing options...
Ian Posted September 16, 2015 Share Posted September 16, 2015 It's amazing how people are so clouded by their views they can't see anything beyond them... the historical range thing above is nonsense. This topic is definitely jumping the shark. Link to comment Share on other sites More sharing options...
Bob Chill Posted September 16, 2015 Share Posted September 16, 2015 Since the DCA sensor has no affect on how much snow falls in my yard I find it REALLY hard to care much about the hard truth on this subject. One thing that's hard to refute is that if you are looking for a location that would have the warmest temps in the region on average on a daily basis, it's hard to beat the DCA spot. If a faulty sensor tossed in an extra couple of degrees it still doesn't change the fact that DCA should consistently show the warmest lows almost every single day and warmest highs more often than not. I'm really not even sure why it's such a big deal. Would there be an outrage if DCA was reading too low? Link to comment Share on other sites More sharing options...
famartin Posted September 16, 2015 Share Posted September 16, 2015 A thermometer's accuracy is important. 32 vs 34 may have resulted in reports of rain when it was still freezing on contact, which directly affects aviation safety (despite the FAA not thinking 2 degrees is important). Plus there is that whole climate change debate. Link to comment Share on other sites More sharing options...
CAPE Posted September 16, 2015 Share Posted September 16, 2015 A thermometer's accuracy is important. 32 vs 34 may have resulted in reports of rain when it was still freezing on contact, which directly affects aviation safety (despite the FAA not thinking 2 degrees is important). Plus there is that whole climate change debate. Absolutely it is. But there are always tolerances(acceptable error) with a sensor. And the test standard must be more accurate than the sensor to provide meaningful validations of its readings. For example, the sensor has a stated accuracy of plus/minus 1 degree C. The test standard(reference) should have a stated accuracy of something like plus/minus 0.1 deg C.(or better) Link to comment Share on other sites More sharing options...
CAPE Posted September 16, 2015 Share Posted September 16, 2015 The question that could be asked about the sensor, is why the one being used has a plus or minus 1.8 degree F tolerance. There are certainly more accurate sensors available. But one cannot claim that a sensor is faulty when it is, in fact, performing as specified. And of course the ability to validate the readings is limited by the accuracy of the test standard being used. Link to comment Share on other sites More sharing options...
Kay Posted September 16, 2015 Share Posted September 16, 2015 Since the DCA sensor has no affect on how much snow falls in my yard I find it REALLY hard to care much about the hard truth on this subject. One thing that's hard to refute is that if you are looking for a location that would have the warmest temps in the region on average on a daily basis, it's hard to beat the DCA spot. If a faulty sensor tossed in an extra couple of degrees it still doesn't change the fact that DCA should consistently show the warmest lows almost every single day and warmest highs more often than not. I'm really not even sure why it's such a big deal. Would there be an outrage if DCA was reading too low? A thermometer's accuracy is important. 32 vs 34 may have resulted in reports of rain when it was still freezing on contact, which directly affects aviation safety (despite the FAA not thinking 2 degrees is important). Plus there is that whole climate change debate. Bingo. Some believe much of the variation probably can be explained by natural processes, others believe it's anthropogenic. <---I'm joking around, but IIRC some believe the equipment/data has been not only inaccurate but intentionally rigged, tampered with, or deliberately left wrong by deceitful humans, to support a certain argument that shall not be named and has its own forum. That's an entirely other allegation than just faulty equipment, or even slowness to address. And makes it even less likely this will ever be resolved--even if it's established over time old data wasn't problematic, conspiracy theories can be highly resistant to data, which can always be "fudged". Although I think people have pointed out DCA temp records aren't used for these purposes, and also I doubt public perceptions are swayed by or even much aware of the DCA sensor. Oy, I can't believe I'm commenting in this thread. Tried to resist but seems like this hasn't been brought up, at least lately, and underlies some of the burning (haha) passion for this topic. Link to comment Share on other sites More sharing options...
WEATHER53 Posted September 16, 2015 Share Posted September 16, 2015 The daytime highs have been brought into proper alignment but there was so much push back on that that they have to take it gradually. Next up will be some form of relocation and/or a mitigation of immediate site radiance The next step is now down to two choices. Place 2/3 other sensors about 150 feet away and see what they measure. Despite some photogrpahs it has Never been clear cut where the observations come from under all circumstances. The last time I was at the office there was some temperature and humidity and rainfall measuring devices on the roof next to the office. The second choice appears to be along lines of covering the ground area around the station out on the property with a tarp and see what happens. If values lower then it would be considered an undue radiance from the ground. It has been debated and affirmed and denied that the current grounds location is where an asphalt road used to be that was abandoned and has deteoriated and become infused with grass but that there may be a residual heat effect from whatever, if any, asphalt still remains on the surfacr or just barely below it . Either way the deniers day is done unless the deniers know more than several state climatologists and mets and other parties are full of baloney along with the Washington Post Link to comment Share on other sites More sharing options...
Ian Posted September 16, 2015 Share Posted September 16, 2015 It's like Howard doesn't even realize I was a co author on the piece that got this done lol. Link to comment Share on other sites More sharing options...
Ian Posted September 16, 2015 Share Posted September 16, 2015 Figuring out where the sensor is takes all of about 10 seconds with Google as well. Link to comment Share on other sites More sharing options...
WEATHER53 Posted September 16, 2015 Share Posted September 16, 2015 A thermometer's accuracy is important. 32 vs 34 may have resulted in reports of rain when it was still freezing on contact, which directly affects aviation safety (despite the FAA not thinking 2 degrees is important). Plus there is that whole climate change debate. Your comments are correct and partially what may have been an issue all along. When I first started on this over a decade ago the first run around is FAA versus NWS. There was a definite policy that this is a highly secured airport and it is only "weather weenies" that are worried about DCA having a low of 18 while Andrews, Annapolis and all others are in single digits. Things like this feed on themselves and increase the lack of concern over accuracy. This cost me a personal friendship and I do feel bad about that but I feel good that there have been steps to bring DCA in line with reality. Link to comment Share on other sites More sharing options...
WEATHER53 Posted September 16, 2015 Share Posted September 16, 2015 It's like Howard doesn't even realize I was a co author on the piece that got this done lol. You had nothing to do with getting done what got done. You did help put the article together. You know I know JS quite well. Link to comment Share on other sites More sharing options...
WEATHER53 Posted September 16, 2015 Share Posted September 16, 2015 Figuring out where the sensor is takes all of about 10 seconds with Google as well. Yes. Those are the photos that have been acknowledged and released. Google does not always have all the infomation for all situations and they cannot provide what they do not have. Link to comment Share on other sites More sharing options...
Ian Posted September 16, 2015 Share Posted September 16, 2015 You had nothing to do with getting done what got done. You did help put the article together. You know I know JS quite well. Oh yeah? And how do you know that? I certainly wouldn't claim it was me that did it but I wanted to do the article and Jason helped push it along quickly. You have some stupid grudge against me for no reason. Get over it. No one said temp accuracy isn't important but this issue is only important to a very small subset of people when it comes to issues of importance. There are multiple avenues to dealing with things like ice not just related to the temp at a spot. Link to comment Share on other sites More sharing options...
Ian Posted September 16, 2015 Share Posted September 16, 2015 Yes. Those are the photos that have been acknowledged and released. Google does not always have all the infomation for all situations and they cannot provide what they do not have. The main array is exactly where it's identified to be. Snow is not measured there partly because walking out into an active airfield to measure snow would be kind of dumb. Link to comment Share on other sites More sharing options...
mattie g Posted September 16, 2015 Share Posted September 16, 2015 The main array is exactly where it's identified to be. Snow is not measured there partly because walking out into an active airfield to measure snow would be kind of dumb. It's too bad that the snow measurers aren't willing to take one for the team. Link to comment Share on other sites More sharing options...
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