Apologies to singer Tony Bennett for the title. Our own “Charles the moderator” writes in with this curious picture from Weather Underground showing downtown San Francisco at about 2:15PM September 8th, 2015.
The disparity of temperature just a few blocks away is quite stunning. In the two temperatures circled in the downtown area yesterday there is a full 14°F (~8°C) difference. Charles adds this note:
These two spots are about 6 blocks apart. No fog and no wind.
The no wind part is backed up by the many circles showing no wind barbs.
One would expect a normal temperature gradient of sorts from the shore to the inland area, due to the influence of the bay, but this gradient is perpendicular to that expected gradient. And there are other examples. At Bush/California Street we have 80°F and a few blocks away at Divisidero and California we have 93°F in the opposite direction of the expected natural gradient. Near Haight-Ashbury, we have an 86°F reading and a 94°F reading just 4 blocks away. In the Richmond District, we have 80°F and 94°F in the Inner Richmond District. Then there’s Mission Bay at 97°F and Potrero Hill at 80°F, and these two stations are approximately the same distance from the water of the bay.
Lest anyone think this is a one-off fluke, I checked this morning at 8AM PDT as I was writing this essay. The screencap is below, note the 81°F and the 67°F near the center, and other examples:
So what is the correct temperature for San Francisco at any given time? I have no idea. Pick a number, any number.
Given that Weather Underground has many weather stations logging data in real time in many cities worldwide, I expect readers can find similar examples elsewhere. It should also underscore that any attempt to use this personal weather station data for science or climatic purposes comes standard with wide error bands.
And despite the usual protestations, siting does matter when it comes to measuring temperature, as this map proves. Cue Mosher rant in 3…2…1
I’d also add that the 97 degree location appears to be on Van Ness – which even at 2 pm experiences very, very heavy traffic.
The 84 degree location is also in a high traffic location, but on the lee side of a hill, in an area with many relatively tall residential buildings, and with only 3 lanes of traffic vs. Van Ness’ 6+ lanes (Franklin and Turk has only 3 south-north, one way traffic light coordinated lanes and 2 west to east lanes vs say Van Ness and Mission which has 6 north-south two way traffic lanes and 3 west-east – none of which are traffic light coordinated.
Lastly, SF has been really hot this past week. In the shade, the temperature is tolerable but anything in the sun is baking.
“So what is the correct temperature for San Francisco at any given time? I have no idea. Pick a number, any number.”
As with the meaningless “global temperature”, there is no “temperature for SF at any given time”. You can record a temperature for one spot, and record one for another spot. But averaging them, or whatever, doesn’t give you a temperature, it just gives you an average of numbers. Physically meaningless.
IMO the most meaningful measure you can have is to log what the temps do temporally, over a Day (min and max temp), day to day evolution (thermal cycle), and seasonal cycle at a single physical location. If you collect a set of locations, you can make some sense of what’s happening at those locations, places without a sensor, could be doing anything and are unknown. Very Schrodinger’s cat.
For years now I’ve been trying to point out global mean temperature is meaningless drivel, at best you can know only what has been actually measured.
I live in the NE suburbs of Washington, DC and keep my readings on a 10th story balcony with a max/min thermometer. It is a north exposure and never sees the sun. My maximum temperature is on average 5-10 degrees cooler than the surrounding stations. In fact my summer maximum temperature is only 86 degrees, while National Airport’s is 98 and has had several 95+ days.
My minimum temperatures seem quite representative and I have checked the thermometer in question with other reliable thermometers and there does not appear to be anything wrong with the thermometer.
So my point is, you can get a very wide range of temperatures in small area based on the nature of your exposure. Those with a vested interest in global warming will obviously avoid exposures like mine and are going to find ones that better suit their interests.