SJC – San Jose International

San Jose International Airport

San Jose International Airport

Original Image

In an earlier posting, I had suggested doing a simple airport Heat Island audit via the expedient of Wunderground.

Then time passes, and over on WUWT, the topic of airports came up again. This was in a thread about the Solomon Islands where the temperature was being measured at an airport:

It was a nice warm sunny afternoon, so I posted a link to the above article, and some temperatures. They showed the airport and the area just down wind a bit warmer than the spaces on either side.

This morning, overcast and cool, makes a nice comparison.

San Jose Airport (SJC) – 62F 7:53 am
Santa Clara (95050) – 61.6 F 8:14 am
Berryessa (Milpitas) – 61.1 8:14 am
Willowglen (95126) – 62.1 8:08 am

Winds “calm” to zero all around. (The term in parens is the search term given to Wundertground to find that station)

ASOS Cookage?

At the bottom of the page at Wunderground, they give a table of stations in the area. I notice this one.

ASOS 63 F See:

The map on that ASOS page shows the SJC airport. Hmmm….

So how can the airport be both 1 F and 2 F hotter than the surroundings at the same time? I smell a “Dig Here!”…

The ASOS stations are used for “QA” on all the others in part of the USHCN QA process as published. And here it is the one that stands out as a degree warmer than pretty much all the others in the list. (The exceptions being a unit on Mount Allison reading 72 F (inside somewhere having coffee?), RAWS CDF portable on Mt. Hamilton 66F, and El Camino – Wolf at 65.1 F ( Looks to be a home near a shopping mall).

The history chart for Mt. Allison shows a fairly steady 70-ish range when you look at the History for KCAMILPI6. Looks very much like a sensor inside somewhere to me (or stuck on a window?)

The portable Mt. Hamilton RAWS record shows a wobble between 65 F and 70F all night long for the History for MTR098. I’d guess it was in an unheated garage all night. Kept stable by the attached building?

The El Camino / Wolf site has a nice web page with neat graphs. Clearly someone “into” weather, but odd that it is running a bit hotter than the surroundings and someone that interested would not notice. See:

Why mention these? Because all the others in the area are very close in range and indicating 61.x F (with some showing lower as they are near colder places, like History for MPEAC1 on Calaveras Road; out in the country toward a reservoir) that is showing 57F. A different air basin and behind a mountain or two. Looks like an opportunity to do an easy UHI study here too. (Dig Dig!)

We have a fairly clear example, though only two times so far, of the SJC airport being hotter, and the ASOS being even hotter, than the surrounding UHI infested area that is itself warmer than the ‘countryside’ nearby.

The Context Map

So for the SJC airport to be reading 62F implies that either they round up (where IS that .x anyway?…) or that it’s a touch warmer than the surroundings. The “nearby airports” box lists 4 airports (one of them SJC) All reported at very similar times. Moffett NAS (Naval Air Station) is also at 62 F, while Reid Hillview (small private planes) is at 61F as is Palo Alto (small private planes but on the other side of Moffett NAS from SJC.

Map of SJC and surroundings

Map of SJC and surroundings

Original image

You can find Moffett field near the water in the upper left. Palo Alto airport is just a bit more up the bay toward that creek entering. Then follow 101 to the right and you reach SJC. More or less north is Milpitas, and if you had continued on that line from Moffett to SJC you will see Reid airport. Willow Glen is that pod of residential area just to the left of downtown San Jose and south of SJC.

OK, so we have 2 very large “international” scale jet ports running 1 F higher than the two private prop plane airports near them. Palo Alto is right on the bay (as is Moffett) and ought to be substantially the same if not identical to Moffett. SJC is just down 101 a few miles and is “near” the bay though not on it. Barryessa is a bit further on toward the hills in the east on a more or less northern path, with Santa Clara snuggled up right next to SJC on the west side (and so a few miles east of Moffett also). Reid Hillview Airport is south east of SJC and south of Barryessa (though a touch east of south of Barryessa, a bit more on a line from Moffett through SJC).

Looking at all this, under a dead calm overcast sky where everything ought to be the same, it sure looks to me like the two major airports are about 1 F hotter than their surrounds. I’m also a bit worried that this looks like it could be a rounding artifact. I’d hate to think that “global warming” came down to “rounding error” as airports round their temperatures… But those two ‘puddle jumper’ airports are also rounded, and they say 61 F.

As a first cut airport audit, I think this system will work. I’ll be watching those stations through the day and seeing if, as the sun comes out, we get some added separation between the stations.

Yesterday. All My Temperatures Seemed So Far Away..

FWIW, the temps yesterday evening were:

SJC (via airport code): 74 F
Barryessa (Milpitas): 72F
Willow Glen (95126) 76.3 F (though this was “north willow glen”)
Santa Clara (95050) 71.9 F

There was a slight wind to the south, toward North Willow Glen, from the airport. ALso, SJC was reported as 43 minutes earlier TOD, so might have had a TOD bias). Times for the other stations were around 8:35 pm.

What I put in the posting on WUWT in comments was:

Using SJC and 95050 that gets a Santa Clara station (San Jose Airport has one side basically against Santa Clara) gives SJC at 74 F with Santa Clara at 71.9 F (Santa Clara is measured 43 minutes after SJC, so there is a chance of a TOD error). Barryessa, California, on the other side has 72 F and the same TOD as Santa Clara.

North Willow Glen, just south of the airport past a couple of freeways has 76.3 at the same 8:35 pm time as Santa Clara but SJC has a S wind indicate with “calm”, so my guess would be that we are getting our usual evening ‘cool’ drift in from the bay sending the SJC heat island breeze toward North WIllow Glen. Sure, it could be plain old UHI added in from downtown San Jose (right on the other side of the airport…)

We generally get a slow southernly drift to the air, so that Willowglen reading could be an artifact of warm airport air drifting in, or just that the particular thermometer runs a bit warm. I’ll be looking around that area for comparison stations to try to sort that bit out.

In any case, I think there is enough here to make large commercial airport temperatures demonstrably suspect in the 1 F range. AND to do a specific ASOS vs nearby audit.

Checking in

For those wanting to check the temperatures themselves, here are the links to the target sites:



Reid Hillview Airport

Moffett NAS

Palo Alto Airport

Santa Clara

Barryessa (Milpitas)

North Willow Glen

If you see anything interesting, please put the facts (temp, time of day, etc.) in a comment. As the overcast breaks up into ‘fluffy clouds’ today I’d expect to see some significant bouncing around as some places are under cloud and others under sun, then stabilization late in the afternoon under clear skys. We’ll see…

So is this the ASOS?

Scrolling around on Google Earth, this was the only thing that looked like it had a tower and some gear boxes around it. So is this the ASOS? It’s near the north end of the runway, off to the side, about where folks put thermometers at airports.

Looks kind of hot and forbidding to me…

About E.M.Smith

A technical managerial sort interested in things from Stonehenge to computer science. My present "hot buttons' are the mythology of Climate Change and ancient metrology; but things change...
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9 Responses to SJC – San Jose International

  1. E.M.Smith says:

    Interesting. Looking at SFO:

    vs. SOMA South of Market,%20California&wuSelect=WEATHER

    it is saying 63 F at SFO while SOMA is 59.3 F, and while down at the bottom of the page, the list of nearby stations is dominated by 59-60F range…

    Houston, I think we have a pattern…

    South San Franciso (that is just north of the SFO Airport) shows cooler too:

  2. E.M.Smith says:

    At 1 pm, more or less, SFO is 66 F while SOMA is 64.3 and So.SF is 59.6 F. So each side of the airport is cooler (and it has cold water on a third…) by 1.7F to 6.4 F. There’s no real “weather” going on right now, so that difference ought to be dominated by equipment and site issues.

    ASOS – 72 F (with a wiggly ramp up from 10 am)
    SJC – 70 F
    Santa Clara – 70.1 F
    Barryessa – 73 F. (Wonder if it gets morning sun?)
    Willow Glen – 70 F
    Moffett – 67 F (getting a slow start on the sunny day…)
    Palo Alto – 66 F (Cooler up north? Perhaps a cool wind starting towards SJC? Says 14 mph from the north)

    While we’re seeiing some impact from the wind, we still have the ASOS showing up as too hot, and Moffett is holding a degree hotter than Palo Alto a stones throw away in the same local microclimate.

  3. E.M.Smith says:

    At 6:20 pm with the sun setting:

    ASOS – 66 F
    SJC – 67 F
    Santa Clara – 64.6 F
    Barryessa – 67 F
    Willow Glen – 67.1 F
    Moffett – 65 F
    Palo Alto – 64 F

    Interesting. Still cooler up north a bit, Moffett warmer than Palo Alto. SJC a bit warmer than Santa Clara, but the ASOS in agreement with SJC. Barryessa a bit warm too.

    Winds from the WNW about 10 mph at SJC. Berryessa W at 6. So there is a bit of a ‘curl’ to the wind. Moving some of the UHI heated air toward the hills.

    Still looking to me like about 1 F of added temperature at the airports.

  4. E.M.Smith says:

    Well, it’s 2:30 AM (and I’m not sleeping… it’s a long story involving lumbar nerve roots…) So what’s the temperature like?

    ASOS – 61 F (winds at about 2 1/2 mph from the NW)
    SJC – 60 F ( wind 4 nnw)
    Santa Clara – 59.4 F calm
    Barryessa – 58 F
    Willow Glen – 59.4 F calm
    Moffett – 59 F calm
    Palo Alto – Not Reporting (airport)

    But this downtown Palo Alto is at 55.4 F,%20California&wuSelect=WEATHER

    The thing I find most fascinating here is that consistent +1 F for the ASOS. Sometimes the other SJC temp is +1 F compared to the surroundings too, but the ASOS always wants to “one up” things…

    Inspection of a bunch of other Palo Alto temps in the “nearby” list under that second Palo Alto site shows broad agreement that it’s cool. Yet Moffett is running about the same as SJ.

    Other places around Palo Alto are not as cool as that second one, with Los Altos sites clustering about 59.4 Sunnyvale about 58.9 and East Palo Alto 57.3 with, finally, Mountain Shadows Mountain View at 59.4 F. So that Moffett 59 isn’t too far out of line with urban areas downwind, but warmer than expected for the fringe of the water. (East Palo Alto is on the bay edge just north of Palo Alto Airport).

    All in all, it’s looking to me like we’ve got an ASOS issue. (And some UHI)

    And given that the ASOS system has been made the dominant source of data and QA reference in the process, since about, oh, 1990 (gee, where have I heard THAT year before…) my strongest suspicion at this point is that the use of the ASOS equipment and sites is why we have a ‘hockey blade’ right after that change…

  5. E.M.Smith says:

    Wondering if this generalizes, I put in Phoenix Arizona. Skyharbour is the major airport there. The temps? Grabbing the first chunk in the listing (it’s SITE, Temp, Dew Pt., R.Hum, Winds, Barometer, Heat Index, Elevation, Time, equip type), what I notice is that the ASOS is running hot at 88 F while nearby is all 82 – 86 F.

    Phoenix is a giant bowl in the desert. Not much natural variation (other than the Camelback hills) for tens of miles in all directions. This much hot variation in the ASOS looks to me like a real problem. (Though I note that the Durango center is as hot. It’s downtown too.)

    APRSWXNET Phoenix AZ , Phoenix, AZ 82 °F 54 °F 38% SW at 0 mph
    28.69 in 0.00 in / hr 81 °F 1115 ft 2:49 AM MST MADIS Website

    ASOS_HFM PHOENIX/SKY HARB, AZ, Phoenix, AZ 88 °F 54 °F 31% WNW at 6 mph
    29.88 in 0.00 in / hr 86 °F 1105 ft 2:45 AM MST MADIS Website

    MesoWest Durango Complex , Phoenix, AZ 88 °F 53 °F 30% WNW at 0 mph
    29.94 in 0.00 in / hr 86 °F 1049 ft 2:45 AM MST MADIS Website

    MesoWest Gateway C.College , Phoenix, AZ – – –
    North at –
    – 0.00 in / hr – 1129 ft 2:33 AM MST MADIS Website

    36th St and Camelback, Phoenix, AZ 76.5 °F 53 °F 44% WNW at 0.0 mph
    29.91 in 0.00 in / hr 78 °F 1214 ft 3:09 AM MST Normal Website

    43rd Ave & Camelback Rd, Sevilla Neighbo, Phoenix, AZ 83.4 °F 52 °F 34% West at 1.0 mph
    29.74 in 0.00 in / hr 82 °F 1108 ft 3:09 AM MST Rapid Fire Website

    APRSWXNET Phoenix AZ , Phoenix, AZ 85 °F 50 °F 30% ENE at 5 mph
    29.76 in 0.00 in / hr 83 °F 1290 ft 2:43 AM MST MADIS Website

    DDMET Tempe, AZ, Phoenix, AZ 85 °F 55 °F 37%
    North at –
    – 0.00 in / hr 84 °F 1372 ft 2:27 AM MST MADIS Website

    MesoWest Osborn @ 64th St. , Scottsdale, AZ – – –
    North at –
    – 0.00 in / hr – 1254 ft 2:33 AM MST MADIS Website

    MesoWest South Mountain Park , Phoenix, AZ 85 °F 53 °F 33% West at 1 mph
    29.97 in 0.00 in / hr 83 °F 2136 ft 2:45 AM MST MADIS Website

    MPR Ray/Thunderhill, Phoenix, AZ 83.1 °F 37 °F 19% NW at 3.1 mph
    28.67 in 0.00 in / hr 81 °F 1260 ft 3:09 AM MST Normal Website

    Ahwatukee – Knox – 48th, Phoenix, AZ 80.8 °F 37 °F 21% SSE at 0.0 mph
    28.56 in 0.00 in / hr 79 °F 1250 ft 3:05 AM MST Normal

  6. E.M.Smith says:

    The airport at Marseille France is a bit hotter than nearby too:,%20France&wuSelect=WEATHER

    Shows it at 75 F

    While nearby it’s 69.3 F and 72.9 F :

    Station Location Temp. Dew Point Humidity Wind Pressure Precipitation Heat Index Elevation Updated Type

    Marseille, Peypin 69.3 °F 51 °F 53% ENE at 2.0 mph
    30.01 in 0.00 in / hr – 1105 ft 12:39 PM CEST Normal Website

    Lamanon 72.9 °F 57 °F 58% NNW at 7.3 mph
    29.99 in 0.00 in / hr 77 °F 386 ft 12:42 PM CEST Rapid Fire

    While Peypin is at a bit of altitude, Lamanon is only a little higher than the 118 ft at the airport.

  7. E.M.Smith says:

    Sydney, Australia is an interesting one too! (This is just too easy…)

    Matraville comes up as the airport. APRS are similar systems to the ASOS. Automated and at airports. Notice that the airport and the APRS listings are about 60 F and the others are cooler… Though Kingsgrove and Potts Point are also hot. Don’t know where or what they are. Looks like a clear airport UHI issue to me.

    The Link:,%20Australia&wuSelect=WEATHER

    The Data:

    Station Location Temp. Dew Point Humidity Wind Pressure Precipitation Elevation Updated Type

    Matraville, Sydney 59.4 °F 57 °F 93% ENE at 1.0 mph
    30.24 in 0.01 in / hr 33 ft 8:49 PM EST Normal

    APRSWXNET Sydney , Little Bay 60 °F 58 °F 93% North at 0 mph
    30.23 in 0.01 in / hr 108 ft 8:34 PM EST MADIS Website

    Kingsgrove, Kingsgrove 60.6 °F 55 °F 83% SSE at 0.0 mph
    30.40 in 0.06 in / hr 200 ft 8:46 PM EST Normal Website

    VK2AFC QTH, Kingsgrove 58.3 °F 57 °F 94% South at 1.3 mph
    30.27 in 0.00 in / hr 0 ft 8:51 PM EST Rapid Fire

    Kingsgrove, Kingsgrove 60.6 °F 56 °F 86% South at 0.0 mph
    30.41 in 0.06 in / hr 60 ft 8:51 PM EST Rapid Fire

    Potts Point, Potts Point 61.0 °F 57 °F 88% SSW at 1.0 mph
    30.36 in 0.00 in / hr 0 ft 7:02 PM EST Normal Website

    Pacific Flight, Sydney 58.6 °F 56 °F 92% West at 0.0 mph
    30.30 in 0.00 in / hr 10 ft 8:51 PM EST Rapid Fire Website

    Kirrawee, Kirrawee 58.8 °F 54 °F 83% SE at 0.0 mph
    30.56 in 0.32 in / hr 50 ft 8:38 PM EST Normal Website

    Gymea Bay South of Sydney near Royal Nat, Sydney 56.6 °F 57 °F 100% South at 0.0 mph
    30.40 in 0.43 in / hr 223 ft 8:51 PM EST Rapid Fire Website

    Sutherland Shire, Sydney 58.1 °F 54 °F 88% North at 0.0 mph
    30.41 in 0.08 in / hr 40 ft 8:48 PM EST Normal Website

    Mosman, NSW, Australia, Mosman 58.1 °F 58 °F 98% ENE at 0.0 mph
    30.12 in – / hr 200 ft 8:47 PM EST Rapid Fire

    Sydney North Shore, Chatswood 57.6 °F 56 °F 95% NNE at 0.0 mph
    30.37 in 0.02 in / hr 307 ft 8:51 PM EST Rapid Fire

    North Ryde Sydney, Macquarie Park 58.1 °F 57 °F 95% East at 0.0 mph
    30.39 in 0.01 in / hr 20 ft 8:48 PM EST Normal Website

    Lynn Park, Denistone West 56.8 °F 54 °F 89% NNE at 0.0 mph
    30.41 in 0.04 in / hr 0 ft 8:37 PM EST Normal

    Sutherland Shire, Engadine 58.5 °F 54 °F 86% SSW at 3.5 mph
    29.88 in 0.39 in / hr 616 ft 8:51 PM EST Rapid Fire Website

    Moorebank, Moorebank 57.4 °F 55 °F 91% SE at 2.0 mph
    30.21 in 0.04 in / hr 72 ft 8:49 PM EST Normal Website

    South Turramurra, near Sydney 58.1 °F 55 °F 88% East at 0.0 mph
    30.39 in 0.02 in / hr 350 ft 8:42 PM EST Normal

    Beacon Hill, Sydney 57.6 °F 57 °F 98% ESE at 0.0 mph
    30.44 in 0.00 in / hr 425 ft 8:50 PM EST Normal

    Carlingford, Carlingford 57.9 °F 57 °F 97% SW at 0.0 mph
    30.44 in 0.00 in / hr 374 ft 8:50 PM EST Normal Website

    St. Ives, Sydney 58.6 °F 54 °F 85% WNW at 0.0 mph
    30.35 in 0.04 in / hr 600 ft 8:51 PM EST Rapid Fire

    APRSWXNET Sydney , Maryville 60 °F 59 °F 96% NW at 0 mph
    30.40 in 0.01 in / hr 82 ft 8:31 PM EST MADIS Website

    Heathcote, Waterfall 55.2 °F 54 °F 95% SSE at 0.0 mph
    30.37 in 0.24 in / hr 705 ft 8:51 PM EST Rapid Fire Website

    Wentworthville, Westmead 57.0 °F 56 °F 89%
    SSW at 0.0 mph
    30.35 in 0.02 in / hr 80 ft 8:47 PM EST Normal Website

    Beecroft, Beecroft 57.6 °F 57 °F 98%
    NE at 0.0 mph
    29.83 in 0.01 in / hr 460 ft 8:51 PM EST Rapid Fire

    APRSWXNET Sydney Hills , Parramatta North 58 °F 56 °F 93% SSW at 0 mph
    30.42 in 0.04 in / hr 390 ft 8:34 PM EST MADIS Website

    West Pennant Hills, Sydney 57.1 °F 55 °F 93% WNW at 0.0 mph
    30.41 in 0.00 in / hr 344 ft 8:51 PM EST Normal Website

    Collaroy Plateau, Collaroy 58.3 °F 54 °F 84% NE at 0.0 mph
    30.50 in 0.00 in / hr 300 ft 8:51 PM EST Rapid Fire

    Castle Hill 57.7 °F 55 °F 92% SE at 0.0 mph
    30.36 in 0.02 in / hr 571 ft 8:44 PM EST Normal Website

  8. Here is the local map centered on KSJC for 8 AM 1 Oct 2010. KSJC fits in fairly well with surrounding sites.

    Note the Enderle Group (SNJSE) reported 59 at 8 AM to the east of the airport up near the base of the mountains. The San Jose RAWS site (RJSC1) had a similar temperature. The Mt Allison (MILP6) report of 73 F is from an elevation of 2600 ft in the warmer air aloft. In fact, the Oakland sounding from 5 AM 1 October 2010 showed 71 F near that elevation.

  9. E.M.Smith says:

    @mark albright: which just raises the question of why the ASOS is warmer than the SJC site…

Comments are closed.