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