UPDATE: We have the photo situation under control, Please don’t go to the Carefree Skyranch Airport as they’ve been getting a number of calls and visits. A follow up report is coming. – Anthony
Since Steve Goddard and I posted recently on the subject of high temperatures in Arizona, this seemed like a good followup to problematic climate data and stations we noted in that post. In my previous post about record minimum high temperatures in Southern California I showed a map with all the new records plotted. But, there was a curious red dot record high temperature “anomaly” on it, 109°F in Carefree, AZ on July 8th:
I thought this was curious, especially since there were no other record high temps set in the state of Arizona in the last week. So, I decided to see what I could find out about the station.
My first visit was to the NCDC MMS Metadatabase to get the lat/lon of the station, plus any other info I could find:
I found the lat/lon, and an indication that it was at the Carefree Skyranch Airport, as seen from this approach photo from the airport webpage:
The photo above shows quite a bit of green for Arizona, I wasn’t sure if that was indicative of irrigation or a wet spring.
When I plugged the lat/lon of 33.8161, -111.9019 into Google Earth, it gave me the location of the NOAA weather station at Carefree airport. Right away something jumped out at me:
Check out the albedo difference due to the airport tarmac asphalt. Warmer there on sunny days possibly? I checked the weather for that day, Thursday, July 8th, and found it was full sun all day.
The red dot signifies the NCDC provided lat/lon. Note, that this was gathered (according to NCDC metadata) with a Lowrance GPS. However, the matchup isn’t always spot-on with mapping programs, plus that, since NWS has the most interest in rainfall data for hydrological forecast verifications, they take the GPS reading over the rain gauge, not the temperature sensor.
I determined that the Carefree station temperature sensor was an MMTS electronic type (on a pole) and that it had two rain gauges.
I also learned that this station was not a USHCN station, but was a Class A COOP station, and does report to the climatological database as indicated by the publish to CD note:
I also learned that the station had been converted from Stevenson Screen to MMTS in 1986:
And that apparently the observer had decided to switch observing times, but NOAA lost track of that info:
A close up aerial view from Bing Maps shows the location in detail. I was able to spot the rain gauges, but not the MMTS temperature sensor on the pole:
Interactive view available from Bing here.
The metadata from NCDC on station location, citing obstructions, shows three trees and a building nearby, all of which are visible in the image above. I’m certain the location is correct:
So what we have is a station near a building, in the middle of a sea of asphalt, in the summer in Arizona. I suppose I’m not surprised it was the lone high temperature record last week for Arizona.
Perhaps somebody who lives in Carefree or knows somebody who does can get a photo of the MMTS temperature sensor from 4 compass points and an overall view. It would be interesting to see where exactly it is located. It is a municipal airport, and it looks like the NOAA equipment is in full view of the public parking lot.
I’m betting it is near the rain gauges. Since one is a tipping bucket gauge, requiring a power cable (if it is a Fisher-Porter type with conical top) then the NWS could have killed two birds with one stone when laying cable fro the MMTS electronic sensor also.
This station data is used to adjust other nearby stations that have missing data in NOAA’s FILNET process, and since it is published on the Climatological CD, may also get used in climate studies of temperature.
I’ll check with my friend, former state California climatologist Jim Goodridge to see if he has the data on one of his CD’s from NOAA, and hopefully we’ll get some data from that station to help tell the story. Or, if anybody knows where to get it online, don’t hesitate to point it out.
Now here is where it gets interesting.
I surmised that the airport might read warmer due to the asphalt environment the temperature sensor is located in. The proof turned out to be pretty easy to find. Thanks to the many private weather stations that Weather Underground logs, I was able to locate a private station in Carefree, AZ just north of the airport and all its high resolution data for Thursday, July 8th, when the record of 109°F was tied at the airport. Here’s the tabular data showing it recording the high of 104.2°F at 3:22PM:
As indicated by the Weather Underground page, the station is a Davis Vantage Pro 2 PLUS model with the solar radiation sensor (notice the watts/m2 in the tabular data), a unit I’m very familiar with because I provide that model via my online business. I have no reason to doubt it being just as accurate if not more than the NOAA sensor. It has a similarly sized GILL radiation shield as the NOAA MMTS. It also has NIST traceable calibration for its sensors.
From the XML feed of observations provided by WU, I was also able to get the precise lat/lon of the private station, which appears to be in the observer’s back yard. I plugged the lat/lon into Google Earth and created the image below using the GE measuring tool and my paint program for annotations:
And people try to argue that airport siting of weather stations, or that siting in general, makes no difference.
You can homogenize rationalize just about anything.
I suggest that the NOAA high temperature record for July 8th, 2010 in Carefree, AZ may very well be erroneous, and a byproduct of location.
UPDATE: Commenter “Regg”, seems to think that the 129 feet elevation change between the two stations (that I didn’t think was large enough to be worth mentioning, since Google earth shows only a 10′ elevation change) could account for “most” of the 5°F difference. I considered this when I wrote the article.
Unfortunately, he’s wrong. Dry adiabatic lapse rate calculates out to about 0.7°F difference if we accept the 129′ difference in elevation between the two stations. – Anthony
UPDATE2: We have the photo situation under control, Please don’t go to the Carefree Skyranch Airport as they’ve been getting a number of calls and visits. A follow up report is coming. – Anthony