This is an example of the Airport Heat Island effect. From Wunderground, I’ve done a capture of the data from SJC San Jose International Airport along with the nearby stations that it reports from that area.
What they show, IMHO, is that the airport is about as “warmed” as the major urban center of San Jose, while both are warmer than the areas just a bit removed toward the more suburban areas (that are themselves UHI afflicted, just not as badly being a bit closer to some undeveloped hillsides). I’ve tagged the data with the time and date when I did the screen capture.
4:09 am 15 June 2012 Weather Station San Jose (KSJC) Elevation 56 ft Clear Temperature 53.6 °F Feels Like 54 °F Wind(mph) 8.1 82 °F Clear Tonight
So what this says is that right now, the airport is 53.6 F and claims a wind speed of 8.1 MPH. The minor problem is that nowhere around it has “wind” and sitting in my back yard (just a few miles away) the air is almost dead calm. Sporadic very calm ‘drifts’ of air at about 1 mph maybe… Leaves in the trees not moving at all. I would guess that the 8 mph was from some airplane, or there is some other local effect generating breezes that are not area wide (such as thermals?)
At an rate, wind disrupts the still air that lets a surface cool most dramatically on a cold clear night. A couple of the surrounding stations have similar temperatures, but many are far cooler. This illustrates two things about the use of Airports as temperature reporting stations, IMHO.
1) There’s a degree or two variation in what is the same air basin with the same weather. Exactly which of these is correct? How can we say that any given basin has “warmed” by a degree or even two when we can get that much change just out of minor siting variations and nearly ALL stations have had changes of about that magnitude?
2) To my quick scan, more of the stations are cooler. It would be best to do some sort of statistical plot of the data, but right now, this is “hot off the presses”. More importantly, from personal knowledge of the locations, those stations that are more suburban and a bit closer to the original environment are the cool ones. The warm ones are nearer to development, concrete and roadways. It’s pretty clear to me that the development around and at the airport cuts a degree or two off the lower temperatures on cold clear nights. Just the pattern we see in the data. “Cold clipping”.
I’ll be putting some comments scattered through this list, giving my assessment of each area.
Weather Stations Station Location Temp. Windchill Dew Point Humidity Wind Precipitation Elevation Updated Type Website San Jose Plant51, San Jose, CA 53.3 °F - 45 °F 73% NNW at 3.0 mph 0.00 in / hr 163 ft 1 sec ago Rapid Fire SJSU-ATN, San Jose, CA 53.4 °F - 48 °F 81% South at 9.0 mph 0.00 in / hr 79 ft 0 sec ago Rapid Fire Lawrence, Santa Clara, CA 53.4 °F - 48 °F 80% ESE at 3.0 mph 0.00 in / hr 69 ft 38 sec ago Normal
These are all heavily urban areas. They all run about the same as the airport. Lawrence is the Lawrence Expressway area of Santa Clara, heart of the semiconductor part of Silicon Valley. SJSU is Sah Jose State University, embedded in the downtown area of San Jose proper and near high rise office buildings and between freeways. They all show a bit of wind, with SJSU showing 9 mph. I have to wonder if there is some local disruption of air flow. They are essentially just to the east of the landing pattern. A bit off the south end of the runway.
Santa Clara, CA 52.6 °F - 47 °F 82% SSE at 0.0 mph 0.00 in / hr 12 ft 12 sec ago Rapid Fire Santa Clara - Lawrence & Monroe, Santa Clara, CA 53.2 °F - 47 °F 80% SSE at 3.0 mph 0.00 in / hr 88 ft 3 sec ago Rapid Fire APRSWXNET Santa Clara CA , Santa Clara, CA 52 °F - 47 °F 84% NE at 0 mph 0.00 in / hr 116 ft 27 min 7 sec ago MADIS
The West side of the airport abuts Santa Clara. Notice that it’s about 1 F cooler. 52.6 F and 52 F. The reading close to the same at 53.2 F is still 0.4 F cooler. It is at “Lawrence and Monroe”. That’s over near the “Lawrence” station listed above. It is the intersection of one of the most heavily trafficked expressways in Silicon Valley with a major road leading to downtown Santa Clara. IMHO the more treed areas of Santa Clara are a bit closer to the original vegetated state of the valley, but still have significant UHI compared to the open grass and orchards of the 1800s.
North Willow Glen, San Jose, CA 58.6 °F - 46 °F 62% NNW at 0.0 mph 0.00 in / hr 125 ft 3 hr 23 min 39 sec ago Normal </preL Willow Glen is a residential area of San Jose just south of, and typically down wind of, the urban core and Airport. It looks to me to be reading significantly high and may have specific site issues along with being downwind of the heat centers of the airport and high rise core. Though with wind at 0.0 mph there ought not to be a lot of warmth drifting in.
APRSWXNET Santa Clara CA , Santa Clara, CA 54 °F - 47 °F 76% ESE at 0 mph 0.00 in / hr 137 ft 26 min 7 sec ago MADIS Berryessa, San Jose, CA 51.0 °F - 49 °F 92% NW at 0.0 mph 0.00 in / hr 131 ft 4 min 18 sec ago Normal
These two make an interesting set. We’ve got a 5 F range between the two of them. I don’t know where the APRSWXNET station is, but it’s an Amature Radio station I think. Berryessa is a more open suburb area toward the east and a bit north from the airport and approaching the hills. It is further from the urban core, but still near a large freeway. It will get the cooling descending air off of the hillsides that characterizes still air cooling flows in the valley. ( Called “The Digger Pine Belt”, the air on the hillsides cools and descends into the valley, letting the upper areas of the hills stay warmer which the Digger Pines like while letting cold air pool in the valley. IMHO this is showing that happening, but unable to reach the airport as it used to do in the past prior to urbanization)
Wooding and Spruance, San Jose, CA 51.8 °F - 47 °F 83% NNE at 2.3 mph 0.00 in / hr 0 ft 20 sec ago Rapid Fire San Thomas/Hamilton, San Jose, CA 52.8 °F - 45 °F 75% North at 0.0 mph 0.00 in / hr 180 ft 4 sec ago Rapid Fire
San Thomas is another major expressway, but further south, and Hamilton is another major cross street. This intersection is a bit closer to the hills on the other (western) side of the valley and more south. Almost a straight line from Barryessa on the other side of the airport and urban core. I’m not familiar with Wooding and Spruance, so can’t comment on it. I just note in passing that two places away from the central concrete jungle are both about 1-2 F cooler.
Sunnyvale - Jasmine, Sunnyvale, CA 54.2 °F - - 92% SSE at 0.0 mph 0.00 in / hr 70 ft 9 min 5 sec ago Normal Saratoga Ave./Doyle Rd., San Jose, CA 54.2 °F - 45 °F 69% South at 3.4 mph 0.00 in / hr 190 ft 52 sec ago Normal Panama Park, SUNNYVALE, CA 54.9 °F - 46 °F 71% East at 0.1 mph 0.00 in / hr 154 ft 3 min 10 sec ago Normal Ortega Park, Sunnyvale, CA 52.7 °F - 44 °F 71% SSE at 1.4 mph 0.00 in / hr 118 ft 16 sec ago Rapid Fire
Sunnyvale is a mile or two further west from Lawrence Expressway. It ranges up to the edge of Moffett Field area (though Mountain View is closer) and is about the same distance from the bay as Santa Clara. It is part of the same “Urban Metroplex”. It would be interesting to find the Panama Park and Ortega Park stations and see what makes those two “parks” different. Why do we get 2.2 F of difference between them. The 36 foot elevation difference implies a bit of separation. Worth a pick at some point. Saratoga Ave. is a major surface street. I’m pretty sure that puts the Doyle station in a UHI area.
Alum Rock Park, San Jose, CA 50.7 °F - 34 °F 52% North at 0.0 mph 0.00 in / hr 203 ft 28 sec ago Normal
Alum Rock Park is a couple of miles more into the hills than Barryessa (though just a bit south of it). The 203 foot elevation gives you an idea. It is JUST outside of the development with houses right up to the entrance. It is a nice rural park with camping type areas, not an “urban grass island”. IMHO, that temperature is fairly representative of the area minus UHI and development. A good 3 F below the heat island.
APRSWXNET Sunnyvale CA , Sunnyvale, CA 55 °F - 45 °F 68% East at 0 mph 0.00 in / hr 127 ft 29 min 7 sec ago MADIS
A nice hot station back down in Silicon Gulch…
Comstock Ln and Park Wilshire Cr, San Jose, CA 52.2 °F - 46 °F 82% East at 4.0 mph 0.00 in / hr 188 ft 1 sec ago Rapid Fire MotherShip, Mariani Orchard, Cupertino, CA 52.3 °F - 46 °F 79% East at 1.6 mph 0.00 in / hr 232 ft 2 sec ago Rapid Fire
Here we get to Cupertino and Mariani Orchard. Years ago when I first came here it WAS an orchard. Now it’s a patch of “last to become apartments” as one approaches the Apple Computer campus. If it is where I think it is, it still as a patch of the old cherry trees. I note, too, that the 188 ft elevation part of San Jose is about the same. A good 1 F below the airport…
AeroDynamic Aviation-RHV, San Jose, CA 55.1 °F - 48 °F 78% South at 4.5 mph 0.00 in / hr 133 ft 4 min 34 sec ago Normal Purdue Drive, Saratoga, CA 51.3 °F - 46 °F 83% WSW at 0.0 mph 0.00 in / hr 242 ft 1 sec ago Rapid Fire
An interesting set. I’m pretty sure that AeroDynamaic Aviation is at the Reid Hillview Airport. They are a flight school. It is surrounded by shopping centers, asphalt, and a freeway or two. Over by Berryessa, but it’s an airport… Warm, too. Not very far from the Alum Rock park either. But what a difference a chunk of tarmac makes… Folks landing at Reid Hillview approach over the Eastridge Shopping Center parking lots and buildings and every so often someone lands on them… Basically it’s an asphalt jungle for a few miles around this place. I think that shows in the temperature.
Saratoga is back over on the west side, up in the lower edge of the hills on that side. Nice and cool away and a bit above the asphalt jungle. More representative of the “small village” phase prior to full paving of Silicon Valley… So we get 51.3 F compared with the 54-55 F of the asphalted areas.
Next up are several more very cold thermometers. Homestead is part of Sunnyvale down near (closer to the hills and near that Orchard area above IIRC). Then another Saratoga that’s even further south and closer to the hills.
Homestead/Kennewick, Sunnyvale, CA 50.9 °F - 42 °F 70% SSW at 4.0 mph 0.00 in / hr 225 ft 15 sec ago Rapid Fire APRSWXNET Saratoga CA , San Jose, CA 50 °F - 44 °F 79% SSE at 0 mph 0.00 in / hr 286 ft 29 min 7 sec ago MADIS Utopia Pl, San Jose, CA 49.7 °F 50 °F 42 °F 76% East at 1.1 mph 0.00 in / hr 301 ft 5 sec ago Rapid Fire Cambrian-Camden/Leigh, San Jose, CA 50.9 °F - 47 °F 85% SSE at 5.6 mph 0.00 in / hr 221 ft 11 sec ago Rapid Fire
Don’t know where Utopia Place is as, but the 301 ft elevation puts it near the edge toward the hills. Cambrian – Camden/Leigh is closer to the urban core, but still out of it. A bit south east from the airport and headed sort of toward Campbell and eventually Saratoga (but closer to San Jose downtown than Saratoga and the hills). It’s generally a well treed area with homes with open
yards and only small scattered shopping centers.
Don’t know where Westmont High School is at, but the elevation puts it a bit away from the airport. Things generally start out at zero at Alviso (just across the 101 Freeway from the airport) rise to about 100 feet modestly quickly getting out of the urban core into the suburbs, then rise to a couple of hundred feet just as you enter the hills that surround the valley. The hills rapidly rise to several hundred feet and are only sparsely covered with houses (and mostly very expensive ones…)
Near Westmont HS, San Jose, CA 52.1 °F - 47 °F 83% SE at 0.0 mph - / hr 260 ft 4 min 4 sec ago Normal SW Sunnyvale, Sunnyvale, CA 50.8 °F - 44 °F 79% SE at 0.0 mph - / hr 500 ft 1 min 7 sec ago Normal RAWS SANJOSE CA, San Jose, CA 49 °F 49 °F 43 °F 81% NNE at 3 mph 0.00 in / hr 674 ft 1 hr 17 min 7 sec ago MADIS Sunnyvale, Sunnyvale, CA 49.9 °F 50 °F 43 °F 77% SE at 0.0 mph 0.00 in / hr 330 ft 9 min 51 sec ago Normal
Looking at the elevation on those Sunnyvale stations, I’d guess them to be in the bit of Sunnyvale that once again gets out of the center of the Silicon Valley bowl, and just at the edge near the start of the hills. Also that RAWS station in San Jose is clearly up a hillside somewhere at 674 ft elevation.
What all this says to me is pretty simple. Where years ago the cold air would be shed by the hillsides and sink to the valley floor, making it colder than the hills, we now have enough UHI to warm that cold air as it sinks into the valley. The airport areas are running a couple of degrees warmer than the surroundings, and that heat grades with distance. It is especially evident when there are nights with still air and clear skies. Then we “clip the negative excursions” off the readings.
Just like we see in the GHCN record where once the thermometers all moved to the airports, the range of readings reduces dramatically and it all comes out of ‘peak clipping’ the cold spikes. The hot side doesn’t get any hotter, we just trim off the cold by a couple of degrees on clear cold nights…
As I type, the sun is just starting to lighting the horizon. It’s now 5:30 AM. Here’s the data capture from 5:27, so folks can see how temperatures developed during the last 1 1/2 hours. On a quick scan it looks to me like the cool areas continued to cool faster and the airport only lost a few 1/10ths F. Soon the sun will be warming the tarmac and it ought to rise rapidly…
But I’m feeling a bit cold and want a cup of Good Morning Jo Coffee.. so someone else will need to “compare and contrast” the two listings…
San Jose International Weather at a Glance Weather Station San Jose (KSJC) Elevation 56 ft Station Select Now Clear Temperature 53 °F Feels Like 53 °F Wind(mph) 8 ther Stations Station Location Temp. Windchill Dew Point Humidity Wind Precipitation Elevation Updated Type Website San Jose Plant51, San Jose, CA 52.6 °F - 45 °F 76% NNW at 1.0 mph 0.00 in / hr 163 ft 3 sec ago Rapid Fire SJSU-ATN, San Jose, CA 52.7 °F - 48 °F 84% South at 8.0 mph 0.00 in / hr 79 ft 3 sec ago Rapid Fire Lawrence, Santa Clara, CA 52.0 °F - 47 °F 84% SE at 2.0 mph 0.00 in / hr 69 ft 41 sec ago Normal Santa Clara, CA 51.2 °F - 47 °F 85% ESE at 0.0 mph 0.00 in / hr 12 ft 14 sec ago Rapid Fire Santa Clara - Lawrence & Monroe, Santa Clara, CA 51.9 °F - 47 °F 83% SE at 4.0 mph 0.00 in / hr 88 ft 2 sec ago Rapid Fire APRSWXNET Santa Clara CA , Santa Clara, CA 51 °F - 47 °F 86% SE at 0 mph 0.00 in / hr 116 ft 30 min 59 sec ago MADIS APRSWXNET Santa Clara CA , Santa Clara, CA 52 °F - 46 °F 79% ESE at 1 mph 0.00 in / hr 137 ft 24 min 59 sec ago MADIS Berryessa, San Jose, CA 51.0 °F - 50 °F 95% South at 0.0 mph 0.00 in / hr 131 ft 3 min 10 sec ago Normal Wooding and Spruance, San Jose, CA 50.9 °F - 48 °F 88% NE at 3.6 mph 0.00 in / hr 0 ft 24 sec ago Rapid Fire San Thomas/Hamilton, San Jose, CA 51.4 °F - 45 °F 78% North at 0.0 mph 0.00 in / hr 180 ft 8 sec ago Rapid Fire Sunnyvale - Jasmine, Sunnyvale, CA 52.5 °F - - 95% South at 0.0 mph 0.00 in / hr 70 ft 18 sec ago Normal Saratoga Ave./Doyle Rd., San Jose, CA 52.8 °F - 44 °F 72% North at 0.0 mph 0.00 in / hr 190 ft 4 min 3 sec ago Normal Panama Park, SUNNYVALE, CA 53.7 °F - 46 °F 75% East at 2.0 mph 0.00 in / hr 154 ft 12 min 2 sec ago Normal Ortega Park, Sunnyvale, CA 51.6 °F - 45 °F 79% ESE at 1.2 mph 0.00 in / hr 118 ft 20 sec ago Rapid Fire Alum Rock Park, San Jose, CA 50.7 °F - 36 °F 57% ESE at 0.0 mph 0.00 in / hr 203 ft 20 sec ago Normal APRSWXNET Sunnyvale CA , Sunnyvale, CA 54 °F - 44 °F 70% ESE at 0 mph 0.00 in / hr 127 ft 27 min 59 sec ago MADIS Comstock Ln and Park Wilshire Cr, San Jose, CA 51.1 °F - 47 °F 85% ESE at 0.0 mph 0.00 in / hr 188 ft 2 sec ago Rapid Fire MotherShip, Mariani Orchard, Cupertino, CA 51.3 °F - 48 °F 90% NE at 1.6 mph 0.00 in / hr 232 ft 4 sec ago Rapid Fire AeroDynamic Aviation-RHV, San Jose, CA 53.6 °F - 48 °F 81% WSW at 4.3 mph 0.00 in / hr 133 ft 3 min 23 sec ago Normal Purdue Drive, Saratoga, CA 50.5 °F - 46 °F 85% SE at 0.0 mph 0.00 in / hr 242 ft 1 sec ago Rapid Fire Homestead/Kennewick, Sunnyvale, CA 50.4 °F - 45 °F 83% SSE at 4.0 mph 0.00 in / hr 225 ft 13 sec ago Rapid Fire APRSWXNET Saratoga CA , San Jose, CA 50 °F - 47 °F 89% NE at 0 mph 0.00 in / hr 286 ft 27 min 59 sec ago MADIS Utopia Pl, San Jose, CA 49.0 °F 49 °F 44 °F 82% NE at 0.7 mph 0.00 in / hr 301 ft 6 sec ago Rapid Fire Cambrian-Camden/Leigh, San Jose, CA 50.0 °F 49 °F 47 °F 90% ESE at 5.4 mph 0.00 in / hr 221 ft 3 sec ago Rapid Fire Near Westmont HS, San Jose, CA 50.8 °F - 47 °F 85% ESE at 0.0 mph - / hr 260 ft 7 min 49 sec ago Normal SW Sunnyvale, Sunnyvale, CA 50.8 °F - 47 °F 85% ESE at 0.0 mph - / hr 500 ft 4 min 59 sec ago Normal RAWS SANJOSE CA, San Jose, CA 47 °F 47 °F 44 °F 89% NNE at 1 mph 0.00 in / hr 674 ft 35 min 59 sec ago MADIS Sunnyvale, Sunnyvale, CA 51.2 °F - 46 °F 81% SE at 0.0 mph 0.00 in / hr 330 ft 13 min 13 sec ago Normal