♫ I left my UHI, in Sannn Frannncisco ♪

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.

uhi-SFO-9-8-15

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:

weather-underground-sfo-9-9-15

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

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117 thoughts on “♫ I left my UHI, in Sannn Frannncisco ♪

  1. And from the studies of chaotic systems, we must know the initial conditions to 5 decimal points to have any chance of predicting the future climate.

    • Let’s remember significant figures. My glass and mercury thermometer is graduated in 2 degree increments. 5 decimal points of resolution is meaningless. You are wading in the fever swamp of misplaced precision, a logical fallacy.
      “…There is a mischievous tendency to suppose that exactitude of statistical handling can compensate for inexactitude or ineptitude of observation [but] neither statistics nor anything else can make a silk purse out of a sow’s ear.” [C. Spearman] https://statsland.wordpress.com/2014/07/03/the-error-of-misplaced-precision/
      San Fransisco is renowned for it’s MICRO CLIMATES. This illustrates how all climate is local.

      • Does anyone have an explanation for why with a couple of exemptions temperature readings over 90F have a wind barbs?

        • Does anyone have an explanation for why with a couple of exemptions temperature readings over 90F have a wind barbs?

          I suspect it’s similar to me seeing that many nights in NE Ohio the winds die out, windy during the day, no winds over night.

        • Since I’m guilty of this, I’ll offer my take.
          NCDC claims measurements are +/-0.1F degree, and especially for older measurements IMO it strains credulity. Now when I average 500, 1000, or a couple million, I think precision can extend to 4 or 5 decimal points. I’ve tried to decipher the proper calculation, to be honest, I’m not sure, so I leave the precision to be rounded as deemed fit, plus since I don’t homogenize or krig for the 40-80% of the planet that isn’t measured I feel my number is far more accurate and precise than what’s published based on the same raw data.
          Lastly, if you do round down to +/-0.1F, there is no increase in temps at all, it 0.0 +/-0.1F since 1940.

    • Well if these city blocks are bigger than 200 km, then six blocks would be outside Hansen’s range for reliable Temperature readings, from a remote thermometer.
      Was there any steam coming out from under some grill on the sidewalk, that might explain the hot spot ??

  2. It isn’t (most likely) an issue with the weather underground stations, it’s that there is a wide range of UHI present that may or may not be in any reading, and the assumptions made are likely nonsense.
    I would expect that most of the measured warming could easily be UHI pollution from man made objects, it isn’t just cities, any place trees and grass are removed will have additional warming.
    .https://micro6500blog.files.wordpress.com/2015/08/july31th2015-8_00am_cleardryuhi-annotated.png
    I live between cities in a town of a few thousand (if that many), next to a 51.3 mi² National Park.

      • A little explanation of these would be nice. I deduce the left one is from readings of surface temperatures with an IR thermometer. Except we’re talking air temps here.
        The right one is muddier than necessary. I stopped (if indeed I ever did) displaying relative humidity on my temperature graph. It’s too close to being the inverse of temperature. I suggest you display just the air temp and the dew point. Dew point shows the changes in the air mass, very useful. Here in New England, the TV Mets spend much more time talking about dewpoint than relative humidity. It’s almost like they know we know that it’s high in the morning and low in the afternoon and really doesn’t tell us ground dwellers anything that isn’t available from air temp and dew point.

        • A little explanation of these would be nice. I deduce the left one is from readings of surface temperatures with an IR thermometer. Except we’re talking air temps here.

          I thought we were talking about UHI and thought IR surface temps were applicable.
          I do need to include time lines on the IR though, but approximately max daily air temp (so 5 or 6 pm), through the evening until Sunrise the next morning. The slope of the concrete was from the shadow of the house moving from the front of the house (starting point) to the asphalt driveway from about 2:00pm to 5:00pm.

          The right one is muddier than necessary. I stopped (if indeed I ever did) displaying relative humidity on my temperature graph. It’s too close to being the inverse of temperature. I suggest you display just the air temp and the dew point. Dew point shows the changes in the air mass, very useful. Here in New England, the TV Mets spend much more time talking about dewpoint than relative humidity. It’s almost like they know we know that it’s high in the morning and low in the afternoon and really doesn’t tell us ground dwellers anything that isn’t available from air temp and dew point.

          Except, you can see how rel humidity increasing impacts the cooling rate of the air temp (or more accurately ground temp), dry air cools off very quickly, humid air not as fast, the earth much much slower, unless it’s covered with grass (and I would presume trees).
          This is why grass, trees, cars, all get frost, and sidewalks not as often.
          Air is just the medium between the earths surface and space that the earth cools through.

      • ” 90 F plus temps have wind barbs and below 90F don’t. How come? Hot air rising along the up slopes?”
        That, or rushing in to back fill convection.
        I get a lot of wind during the day that drops to nothing at night, day after day at times.
        Now I do live 3/4 the way up a valley, but it’s actually flat here.
        So I don’t know, just I’ve been surprised by a lot of what I see my surface station recording.

  3. It should be pretty easy to separate the UHI effects from the noise effects with a little statistical analysis on the time series. If the hot spot jumps around, it’s noise. If the same station is always the high one, it’s UHI of one form or another.

    • The variation in temperature readings is due to the hills of the city. Note the extended line of 90+ F temps along Market St from east to west. That line of high temps sits in a valley which is surrounded by hills on 3 sides, only the east end is open to the SF Bay. All of the other hot spots are also sheltered bowls within the hills. I grew up in the Marina District with all of the Italians back in the 1950s.

  4. From experience with my own weather station I suspect sun/shade may be a large part of the explanation.
    Despite having a sunshade, it is still influenced by the sun and is no substitute for a proper Stevenson Screen.

    • If you put a proper Stevenson Screened station near a concrete sidewalk, in a grassy field, and a shaded woods all within a a few hundred yards of each other they will all read different temps, especially if there isn’t much of a breeze.
      You can feel it just riding a motorcycle riding through the shade of a tree.

      • Micro6500. I too noticed the temperature differences when riding a motorcycle into and out of a small town of 20000 in the summer time. Also big changes were noticed when I defended into a valley of 100 feet or so.

      • That is essentially a personal experience of the fact that all temperatures are an intrinsic property of one object. Averages of different ones over space and time yields a statistic about the set, but not a temperature.
        In SF I would regularly shift side of street to get sun or shade and a 10 F or so change of comfort. Similarly, streets aligned with wind cool, those cross wind not so much.
        The whole farce of global warming rests on the fraud of averaging temperatures and calling it a temperature change. Intrinsic properties make that a funamental and uncorrectible error.

    • Yes. Makes one wonder if their is any calibration of instruments, meta-data collected, or any quality control. It is easy to put our an array of sensors, collect the data, and never look back. Apparently there are no standard citing criteria, or periodic checks on the equipment or data. Shoddy and irresponsible work.

  5. Was there a update lag on some stations I wonder?
    I have noticed on Canadian parts of the Wundermap that when you look at the station ID, it isn’t always correct for the location shown. I collected some of these incongruities and notified Weather Underground using their strange correction notification process but it seems like an ongoing problem. The map is not perfect.

  6. I’ve been keeping my own very personal record of temp, rain, etc. here in Mechanicsville, a few miles outside of Richmond, and comparing it with the record published in the Richmond Times-Dispatch and originating at RIC, Richmond International Airport, which abuts the city of Richmond (or Henrico, for part of it) to the west and north, and fairly open country, albeit crossed by large highways, south and east. Obviously, my own record is subject to many flaws and vicissitudes, though I do my best to observe the actual high and low right here at my house, which sits at a border of town and country. There are no street lights here, but I can–if I listen closely–hear the I-295 traffic on winter nights, a few miles to the west (in summer, the insects are too noisy). So my location, while close to developments and at the edge of a quiet neighborhood with acre-plus lots, is still much more rural than the airport.
    I started my record in summer of 2013, so it’s been going on for just over two years. In that time, the high temp here has rarely matched or exceeded that at RIC, and the low has sometimes been quite a bit lower. On average, I’d say the difference is fairly consistent at two or three degrees F. I also compare that average with the long-term average (which the paper calls “normal” and I do not, for reasons given elsewhere on this site), and it is rather consistently below average out here in the sticks. What I lack, and wish I had, is any sort of long-term average or even a long-term record, for here in Mechanicsville. Are this year’s figures at, above, or below the long-term Mechanicsville records? I have no way to know; there seems to be no weather station here.
    Much as I enjoy keeping these records, I have not offered them to the Weather Service or anyone else, since I can’t vouch for their accuracy. My instruments are simple and rough, and my times of checking are irregular. I like what I have, but can’t imagine it would be of scientific use. I shall continue to have my fun.

    • Living in the city, I too compare my back porch thermometer (which I have calibrated vs. a lab quality thermometer) reading to the RIC readings and find that mine are usually warmer, sometimes as much a 5 degrees F. There’s your UHI for ya.

    • I lived SW of Pocahontas State Forest for 10 years. It wasn’t unusual for me to put the top down on my car leaving work south side of Richmond, but get a chill riding through the creek bottom on Qualla Rd by the forest. I never measured the temps, but I’m sure the difference was more than 5 degrees. It could have been 10.

  7. Not as dramatic, but this past June I had occasion to be a few miles outside of a city (official population 58,000 + or -), and noted the temperature as 82 degrees F. As I came into the outskirts, I watched to see if I could perceive an UHI, and sure enough, the closer to the city “center” (western cities are a bit more diffuse than their eastern counterparts), the temperature rose to and settled at 89 F. The local “bank” temperatures were reporting 90, give-or-take, so I have every reason to believe the unit I was using had a measure of accuracy.
    UHI is alive and well!

  8. “So what is the correct temperature for San Francisco at any given time?”
    I’ll bet my Big Oil check that it’s always the highest that is “correct”. The lower values are then “corrected”.

    • No. The higher value is correct for this year, but some of the lower values are correct for last year, and more of the lower values for the year before that, etc.

  9. A place I sometimes work, near the Bay, a few miles south of Downtown … orientation of glass covered buildings makes for a de facto solar reflector array, like a sliver of the ones in the Mojave. Stand at the right point in the parking lot and you might reasonably worry about ill effects to health. No birds scorched thus far, but that’s only because it’s a sliver of an array.

  10. Thanks, Anthony.
    The correct temperature for San Francisco, or anywhere else, is the one measured by satellites.
    Thermometers are way too much affect by the micro-climate around them, man-made and natural.

    • Note that the instructions say nothing about the need to meet certain conditions if you want to be able to register your station.
      So you can’t believe their numbers.

      I don’t really disagree, but I will add that a large number official surface stations aren’t any better.

  11. From my experience at work checking to see if I want to go outside for our post-lunch walk, there’s a lot of error in them thar Wunderground stations. There’s a lot of variation in station quality, siting, and maintenance.
    I won’t take the time to learn which stations in the SF area are untrustworthy, but I’d start there.
    Next I’d pay attention to all the microsite issues around SF. Between the cold Pacific and the hot Silicon Valley there’s no such thing as typical temps. (To say nothing of things like the hot AG areas sucking in cold Pacific air in the summer (cue Mark Twain)).
    Don’t need Mosher to rant about SF weather – and I’ve never lived there….

    • “Silicon Valley”
      Do you mean Santa Clara Valley?
      I had a sail boat in the bay for a few years. It took me a long time to find a marina with little fog and wind. Just a half mile either direction there was lots of fog and wind.
      The weather is highly variable in California. Seattle has more sunny days than Sacramento in February. At 2000 foot elevation in the Sierra foothills, it most often warm and sunny in the winter and really ugly at lower elevations.
      California is beautiful place if you can tolerate a clueless government that tells you how to live.

      • Santa Clara Valley is the right term. I live in New Hampshire but used to attend a week-long computer networking meeting in San Jose in Feb/Mar. After my sister moved to Berkeley I found a great little book on Bay area weather through the seasons, bought it, and left it with her, hence my delusion of knowing something about your weather. My first trip to California was to start my first ever longer than one day bicycle in 1974 (from Palo Alto to Billings MT via Canada), so I learned something about coastal weather way back then!
        I prefer New Hampshire. A lot of weather in a small place. We pay our 424 legislators $100/year each (they’re worth every penny), and if they get too cocky, our constitution’s Bill of Rights commands us:

        [Art.] 10. [Right of Revolution.] Government being instituted for the common benefit, protection, and security, of the whole community, and not for the private interest or emolument of any one man, family, or class of men; therefore, whenever the ends of government are perverted, and public liberty manifestly endangered, and all other means of redress are ineffectual, the people may, and of right ought to reform the old, or establish a new government. The doctrine of nonresistance against arbitrary power, and oppression, is absurd, slavish, and destructive of the good and happiness of mankind.
        June 2, 1784

  12. I’ve seen days in Salt Lake City where the temperature at the airport and the temperature at the U of U campus were more than 20 degrees apart, really not well explained by a 700 foot difference in elevation.

    • Years ago, we lived in Superior, WI, right across the river from Duluth, MN. Duluth is on a hefty ridge–really a low mountain–about 900 feet above the level of Lake Superior, so that the weather on top (and past the top) of the hill can be markedly different from that on the lakeshore, especially if there is an onshore wind. The weathercasters there usually give two temperatures: at the airport (on top of the hill) and at the lakefront. I have heard them close to 50 degrees apart (“It’s a warm one over the hill, 91 degrees; but with the east wind onshore, the lakeshore temperature is a brisk 42 degrees”). It’s not commonly that drastic, of course; but the nature of the place is that a sudden wind change can drop the temperature deeply and abruptly, from (say) the 80s to the 40s in a few minutes. That can be uncomfy if you are in swim gear next to the lake. The difference can be even greater when the ice is late going out. The year we moved to Superior, there was still ice in the harbor–lots of it–until the 10th of June, so sudden breezes off the lake could actually be at freezing temperature close to shore. I still have to say that Duluth-Superior may have been our favorite of all the places my wife and I lived, much as I love Virginia now.

  13. In my view, thermometers in city centres always give misleading results, buildings, heated in winter, air-conditioned in summer, cars with engines running humans emitting 200 watts of body heat and last but not least asphalt, stone and brick which emit heat long after the sun goes down.
    The first house we bought is about 300 yards away from where we now live, our first house had a north facing back garden, our current house has a south facing back garden. The difference in temperature after the Sun had set was substantial due to the bricks of the houses and he concrete patios absorbing the heat energy from the Sun and emitting it back again at night

    • And in our case with all of our illustrious cloud tech places with server farms (yep, server farms in downtown high rises, we’ve got ’em), the added thermal output from all the HVAC creates micro-micro-climates.

  14. Didn’t we read, some months ago, about a high-rise in New York that had mirrored windows, and was focusing sunlight into a small area? Any chance that this is something similar; a solar “death ray” caused by nearby mirrored windows?

  15. In field studies, this is why we use replicated random sampling with an adequate sample size.
    The fact that this has NEVER been done by any of the data employed to portray global warming, climate change, climate disruption, global cooling simply means that the data is trash. The variance of a sample size of one is infinity.
    This has been the case for the last 30 years of BS and remains so today. For satellite data too or did you not consider that one sat still a sample size of one.

    • “For satellite data too or did you not consider that one sat still a sample size of one.”
      Satellites are calibrated against weather balloons–and each other.

      • Uh huh, yeah /skeptical. Have you ever done the basic calculation to determine the sample size required to accurate determine the mean of any day’s temperature to the “closest subdivision” of a degree reported ? How many satellites did you say you have ?
        Sadly, climate science is soft science like sociology at best or pseudo-science at worst. But since they claim global warming causes smaller brains, perhaps that is the best we can do.

      • Forgot to mention that lovey episode of sat data reporting something like ~ 458 C in large portions of the Lake Michigan area – all going into the permanent data set, we are told. They fly weather balloons in that one ?

  16. I have seen the temperature change 10 degrees caused by elevation changes driving into San Francisco. Just moving a station half a mile would have a bigger effect on temperature than climate change.

  17. looking at google maps for the higher reading one in the second screen grab, that 81degree temp
    it is RIGHT next to a large apartment complex with HUNDREDS of angled solar panels. would it be possible that the sunlight reflection from-some- of the panels is influencing said station.

  18. Temperatures in the mid 90s in some points at 8 AM? This sounds to me like some poorly sited stations being affected by sunlight. I suspect the hotter stations are getting air heated by a nearby sunlit surface. Another thought I have is air heated by air conditioning condensers, although I wonder how much there is of that at 8 AM in San Francisco.

    • Oops, now I see the time was 2:15 PM. Meanwhile, I still think that the various stations are having very different effects from poor siting, and the hotter ones are being affected by nearby sunlit surfaces and/or air conditioning condensers. I think the inland air temperature in San Francisco at that time was in the low 80s.

      • Yes, there was a minor sea breeze yesterday and it had in fact kicked in by 2:15 PM, at least it had in the northern part of the peninsula. Even prior to the sea breeze the offshore winds driven by the double barrel high would have exerted cooling in the concrete canyons via their sheer amount of mass flow.

    • Another thought for variation in San Francisco: Temperature inversions are common there because lower altitudes of the air there are often cooled by the ocean and the bay, while higher altitudes even as low as some hilltops and tops of tall buildings do not get such cooling. I noticed this while riding my bike up and down two hills between the Golden Gate Bridge and Muir Woods on a day when the non-water-cooled layer of air was very warm.

      • I just checked the 3-day weather history for San Francisco downtown and San Francisco International Airport, for times around 2 PM on 9/8. There was indeed a large variation of air temperature. Temperatures closer to 80 look like that occurred in air that was cooled by nearby waters, and temperatures around 91-94 were in air that had less or no cooling by nearby waters. It looks like wind overall was very light, and sea breezes had effect varying widely with location and elevation.

  19. It must be global warming at the block level. Send in the Census Bureau to investigate and track over time.

  20. IPCC AR5 didn’t deliver a solid number for mankind’s CO2 contribution between 1750 & 2011 (+/- 76% sq rt sum of squares), the added 2 W/m^2 of RF due to that increased CO2 is lost in the magnitude and uncertainties of the global heat balance esp. the water cycle (clouds -20 W/m^2 +/-?), IPCC AR5 admits their GCMs didn’t model the hiatus/pause/stasis/lull (because their CO2/climate sensitivity is way too big).
    IPCC hasn’t a climatological clue. Nuff said.
    All the other discussions are academic white noise, moot, sound and fury signifying nothing.

  21. No urban temperatures should be included in world temperature data. If we attempt to compare present temperatures with temperatures a couple hundred years ago, or even earlier, we should only compare areas that are similar in landscape to end up with a reliable assumption. Again, no urban temperatures should be included in world temperature data if one is to make any comparison between past and current temperatures.

      • Absolutely correct. And this is the giant flaw that is studiously ignored.

        If we eliminated all that was flawed, there would be nothing left, and Mosh would have a hard time claiming we know enough to act now.

  22. I watch my little Wunderstation (ICUMBRIA1) like the proverbial hawk and this morning’s temp graph demonstrates something but I’m sure quite what.
    Situate at the end of a large garden on the SW side of a small (Pop~5,000) town and looking SW over farmland, all of it grassland for cows/sheep. Not a lot of trees and alt~100m. Most definitely not any sort of ‘built-up-area’
    An English ‘A road’ about 600 metres away but almost zero night-time traffic. No industry worth talking about, esp not at night, sleepy sleepy sleepy.
    All night the wind was drifting N to S, with 5km/h ‘gusts’, otherwise calm.
    Every time the wind moved, the temp moved, by about 1degC over 30 mins then drifted back down to the night-time cooling rate.
    Even after sunrise, the graph became a (rising) mirror image of the night-time, bumpety bump bump.
    If that can happen, at night, in ultra-rural here, how on Earth can that mega-event at daytime Heathrow last month be trusted?

    • I’m confident the little gusts were disrupting the temperature inversion caused by radiational cooling. At least, if it was clear overnight. What generally happens to me in New Hampshire on clear, windless nights includes:
      Dawn: low temp for the day is reached, grass has dew or frost. No wind because the temperature inversion blocks what may be only 10-100 feet above me.
      Morning: Temperature climbs quickly, grass dries out, inversion weakens and then get blown apart. The wind now mixes down to the surface, and the sun has to heat a much larger volume of air to raise the temperature.
      Afternoon: warming either continues well in to the afternoon or it reaches a plateau if we have a fetch of Canadian air. Radiational cooling peaks along with the temperature. (Duh, but your mother probably never taught you that.)
      Evening: after dark, radiational cooling continues. As the ground cools, the air cools, the temperature inversion gets reestablished unless it’s a windy night.
      Repeat.

      • Rick, the IR thermometer still shows my driveway warmer than other surfaces at sunrise (and far warmer the the sky).
        Then a question, how do you tell how thick the surface inversion is?

  23. There was a similar situation in the SW part of the Denver area where I live. There was a station that was often 15-20 degrees higher then it’s closest competitor. I complained once to Weather Underground and the station was removed promptly. Although is showed back up several days later.

  24. So, let us consider the krigging method of determining an unknown temperature, let’s say at the corner of Market St and the Central Fwy in the second map — the station shows 67….the surrounding “known” temps are 81, 74, 72, and 70.
    Using this marvelous tool for determining temps of missing stations, we would get some temp (this is just a guess, mind you) of around 75 or so (the missing point being closer to 81 than the 72 and other 70s).
    Krigging or other homogenization methods can never ever return a result that is higher or lower than the highest or lowest surrounding temperature (or monthly average, which is what I believe is “krigged” in the BEST method).
    Look over the maps shown here (ignoring the scale, assume that this is a national or continental map) and find how many, what percentage, of stations show temperatures outside of (above or below) the range of the four nearest surrounding stations.
    Ashbury Heights at 74 — nearest neighbors 69, 71, 70, 68
    The centreal station marked 81 — nearest neighbors 72, 7, 73, 70
    16th and Folsom at 64 — nearest neighbors 70, 78, 72, 74, 67
    Lower Hasight, just off Castro st at 75 — nearest neighbors 71, 64, 70, 74, 73
    That’s five at just a quick glance, off this little map — all five stations, if they had been missing and their value determined by krigging/homogenization, would not even be close to the actual value, throwing any average of “all stations” off by a large margin.
    Just sayin’.

    • Krigging or other homogenization methods

      And there is much said about just needing Latitude and Altitude to get really close, except I live where the jet stream flip, flops back and forth over heard, making a 10 or 20 degree temp differences, and it can do this over a day or two.
      See the dew point, a good indicator of the source of the surface air
      https://micro6500blog.files.wordpress.com/2015/05/may-8th-26th-2015.png
      You don’t get anything much more chaotic than the jet stream. How do you krig and homogenize around a dividing line that is constantly moving?

  25. CLIMATE IS NOT WEATHER!!!
    err…wait….
    WEATHER IS NOT CLIMATE!!!
    Wait, that isn’t quite right either….
    IT’S A DRY HEAT!!!
    ….never mind….

      • Climate is most accurately defined as a taxonomic ranking of Biomes (biological communities that are shaped by the regional environment) that are easily recognizable at a glance. They are mapped with great imprecision. http://oceanservice.noaa.gov/education/pd/oceans_weather_climate/media/climate_zones.swf
        Most people, without a great deal of schooling, can easily tell the difference between Tropical/Temperate/Polar, Wet/Dry, Maritime/Continental, Desert/Mediterranean/Rain-forest. That is because Biomes tell us directly what the average weather is over a lot longer time frame than simply 30 years. Without using thermometers or records. Imagine that!
        Climate science: Hijacked by politics.

      • That would be for “weather” measured by instruments which over the 30 year span were far from (and not downwind of) any significant land use changes. The main problem with our climate records is that far too many weather stations have had significant land use changes very near to them. There are a significant number of weather stations which have survived with little if any land use change, however these are homogenized with the stations which have had significant land use changes. I hypothesize that even small towns (~5,000) have a measurable UHI. Any of these small towns which are either these near jobs or near enough to urban centers to encourage development have had urbanization over the past 50 years.

  26. “I expect readers can find similar examples elsewhere.” Absolutely. I live in a suburban/semi urban area in Michigan. The Weather Underground website provides readings for at least 10 nearby stations. The Official Weather station is at the international airport about 13 miles away. On some days I’ve seen variations as much as 10 degrees within 1 mile….. and none of the stations agree with the official temp …. but the normal variation is about 3 degrees (Fahrenheit). Who ya gonna believe?

  27. I lived in SF for 5+ years, and I see no surprises in this picture.
    First of all, the color key at the top shows that these pictures mix temperature reports spread out over the length of a day, as well as over the size of the city. But more to the point, this is a coastal city at the mouth of a large bay, so of course there are going to be massive air flows through it on a twice-daily basis.
    I lived near the top of Twin Peaks, the highest point in the city, which is about at the point Market St. runs off the bottom of your map. Go up there in the middle of the night, no matter what part of the year it is (I suggest the parking lot at Portola and Clipper) and you can watch the fog blow in from offshore — easily fast enough to see — until by about sunrise, it has covered everything. Of *course* this carries large temperature changes with it. It couldn’t possibly be otherwise.

    • Actually, coastal stratus is fairly rare during the winter / rainy season. Not enough upwelling and very little onshore push. During the dry season, yes, you are correct.

      • We’re already getting into Fall mode. Several other indicators of that. For example the nearly dry cold front about 10 days ago. Fronts like that usher in Fall. Who knows, we may lose the fog early this year, overall. Maybe little to no fog after the end of the month.

  28. I had the opportunity to spend a few months in San Mateo at the end of the last millennium while moving a data center from downtown San Francisco across the bay to Hayward, and the experience was an eye-opener for the definition of microclimates. The city sits on the north end of a mountainous peninsula sandwiched between the cold ocean currents of the Pacific Ocean and a warmer San Francisco Bay, with the hot desert interior of California just a few miles away. It is possible to draw a line through San Francisco only 30 miles long where the western end is shivering in the cold 55°F Pacific waters of the California current and the eastern end is baking in the 100°F desert east of San Leandro. In between, the altitude changes from sea level, climbing to between 500 and 1500ft (depending on exactly where you draw the line), back down to sea level, up to 1500ft, and back down to 500ft in the hot interior with the temperatures fluctuating wildly along this line from generally cold to generally hot. The building we were vacating in South San Francisco was so cold there was no air-conditioning, except in the data center. The building we were moving into at Hayward just 14 miles away was always too hot, despite having a kiloton of air conditioning.
    We used to pick our lunch venues in San Francisco according to how we were dressed … too cold, move east a block or two; too hot move west a block or two. It was crazy. Fortunately enough, the Ghirardelli Chocolate Factory in Ghirardelli Square situated on Beach St near the Hyde St cable car turntable seems to always be at that perfect temperature where the chocolate is just below its melting point, surely one of the great happy accidents of microclimate geography.
    But don’t take my word for it… the source of all knowledge has an article on microclimates that mentions San Francisco … https://en.wikipedia.org/wiki/Microclimate
    So yes, nobody can ever agree what temperature it is in San Francisco, because two people standing on opposite sides of the same street can measure temperatures that differ by 5°F. If you don’t believe me, then I suggest you walk around the town – just make sure that one of your stops is Ghirardelli’s.

    • Where I grew up in Ohio, there are no microclimates like we have in the West. California temperatures can vary by 30 F within 15 miles or less. It is currently 74 F in Morro Bay and 100 F only 17 miles to the northeast in Atascadero. 10 miles south of Atascadero in Santa Margarita, it is 105 F (all from Weather Underground).

      • Where I grew up in Ohio, there are no microclimates like we have in the West

        But we can have 3 or 4 seasons weather in a day or so without going anywhere (due to the movement of the jet stream).

      • The NWS reported the temperature extremes for the U.S. yesterday were both in California. Boca Reservoir at 26F and Death Valley at 116F. So if you drive a little farther than 15 miles, you can experience a 90F temperature swing from low to high.

  29. Re: Ric @1058
    I remember Santa Clara Valley when It resembled the writing of Jack London.
    Love New Hampshire too. Went camping there when stationed at the navy base in Newport, RI. Another good place to sail except the winters are brutal. Sailed in shirt sleeves in February in SF Bay. Also needed my winter coat in July.
    I lived a lot of places as an adult but swore I would not go back back to California with children because of the schools, drugs, and gangs. When you have just spent a brutal inter working near Detroit, and you that job offer from Cleveland is looking good; then you get a call from a nuke plant in California, it look like a good choice. I thought the schools might be better in a small town. Half the teachers are draft dodgers or quitters.
    Because of politics, the plant I worked closed. Subsequent to California, we have had school age children in Washington State and Virginia. Great school and a nice house only requires one income. Good schools, low taxes, and no crime. It is a pleasure to watch county government work well by serving the community not some screwball social justice agenda.

  30. I think this emphasises one of the flaws in the alarmist position. Who cares about a change in temperature of 1,2 or even 4 degrees. The people who live where the temperature is recorded as 14 degrees higher I suspect haven,t been fried. I defy anyone to accurately know the difference between the temperature now and 50 years ago without reference to a thermometer. The 2 degree variance plucked by warmists is less than the adjustment people make by raising or lowering their air conditioning of their homes yet we don’t have any repercussions. When you have variances of the magnitude highlighted in this article you realise ( or a person not indoctrinated by AGW theory) that just the error bars of local temperatures are probably greater than the amount of warming that has occurred in recent history. When you can’t vouch for accuracy of data how can global weather bureaus vouch for the accuracy of adjustments. It’s a total farce.

  31. Thats just the san fransisco marine/fog influence. Just drive across the golden gate and 4 miles north at the same elevation and it could be 90f while its 50f at the wharf in the city.

  32. Anthony, as an air quality meteorologist for over 40 years, I totally agree with your statement “siting does matter when it comes to measuring temperature”. The sensor shielding, aspiration, and placement at the site also matter greatly, as well as sensor quality control and quality assurance. And the siting for one purpose may not be suitable for another.
    Here’s a photo I took of an air quality and weather station placed at the top of the tallest building in Houston back in 1986. The shielded and motor-aspirated temperature sensor can be seen about 2 meters above the top of the building.
    https://www.flickr.com/photos/oz4caster/8060698271/
    I enjoying checking weather measurements on the WunderMap, but most of these measurements are not very representative of larger scales, especially for wind, and many are essentially micro-scale monitors that do not represent larger areas very well. Usually there is little or no information about the monitor siting, although if the location is accurate you can zoom into the aerial imagery view to get a rough idea. With your detailed analysis of USHCN monitor siting I’m sure you are acutely aware of this problem.
    This map raises some interesting questions about estimating “global temperature” and associated anomalies. Representativeness of selected inputs is critical. I personally like the CFSR approach. I can’t imagine using only the GHCN data as input to drive real-time weather models for surface temperature. Not that the CFSR data are perfect either, but there is much better coverage. It’s interesting that the CFSR data show more of a downward trend in recent years compared to GHCN derived NCEI estimates.
    https://oz4caster.files.wordpress.com/2015/03/cfsr-ncdc-ann-1979-2014.gif
    There are many locations that present a challenge for the meaning of “surface temperature” measurements, and and urban street canyon environments are one of them. Vast jungles are another and probably cover much more surface area than urban environments. How do you represent the surface temperature in the middle of a jungle or in the middle of skyscrapers or at the top of the numerous unmonitored high mountain peaks around the globe? Again, I like the approach of using the data we use to initial the global weather forecast models to provide our best general representation that we have for surface temperature.

    • As you were an air quality meteorologist for over 40 years, I would like to know what the precision was of the instruments that you used, especially thermometers? I used calibrated glass thermometers in the oil industry for over 25 years, and even the expensive ones had an accuracy of +/- 0.5C…

      • Mark, I worked in the public and private sector and the temperature measurements associated with air quality measurements were obtained using shielded, motor-aspirated electronic temperature sensors logged on data loggers as five-minute averages and processed into hourly averages. The sensors had an accuracy of about +/- 0.5C. The public temperature sensors were usually mounted on towers with the wind sensors at about 10 meters above ground level. The private group monitored temperature at about 2 meters as in the photo I provided. Both groups provided annual independent audits and data validators reviewed the data for quality assurance.

  33. Another thing to consider is the temperature sensor/computer interface.
    I was responsible for the decay heat removal system at a PWR nuke plant that had been shut for an extended period of time. It was common practice in the navy and BWRs to cool the plant done, turn off the pumps, and allow natural circulation to mix the water while the plant slowly heated up. At some point ambient loses would be greater than decay heat so cooling pumps would not have to be restarted.
    I could program the plant computer to record incore thermocouples. I noticed there a were random temperature jumps of about 10 degrees. The computer recorded data set every two minutes and the temperature jump would be gone. Of course the temperature did not change.
    Error is normal when measuring things. I had tanks containing boric acid that we sampled periodically. There is no mechanism to change the concentration (by design) but the chemistry guru tells me to expect out-of-spec samples. It is a statistical thing. Take another sample and it is very unlikely statically for the random reading to repeat twice in a row.
    I when we do stuff at a nuke plant, we check to see if we get the expected results. I was running a test and got the expected results. The NRC observing the test goes running down the hall going OMG, OMG. Why was I not concerned because the test results did not match the expectations of a Washington DC bureaucrat? My agenda is based on science and years. While there are things we can not take credit for in modes, real life is not a model.

  34. I’ve had a Wunderground station for almost 8 years. Located in Southern Vermont, the elevation is around 1700 ft. Other stations in the area are located in the surrounding valleys. My station is the default for reporting by Zip Code lookup, as there are no others closer. However, it will not show up if it is a calm morning and the valleys are cooler by more than 3 F than my station is reporting.
    I talked to Wunderground about this behavior and they told me they essentially turn off reporting for a station if it is outside some magical boundary compared to it’s peers. They have no concept of elevation or station location (in some of the other spots, the sun doesn’t rise till after 9AM.)
    Note that this data censure only happens if you ask for it by location, like Zip or City or Airport. The station is always available on-line, it just is not considered in the overall location average. In my case, being the only station for a Zip, it is ironically too apparent.

  35. As an avid paraglider I can tell you that the tempature differences are quit common in nature as well. Depending on the Suns angle, the materials being heated, the wind pushing thermals together in certain areas. You may note that, within an hour or so, that gradiant might disappear altogether and another one pops up some place else.

  36. Just to make sure, and I apologize if someone else has already asked, but are all the readings reported at the same time? Is there any possibility that the lower temperature reading lags by a few hours? I’ve seen that happen before….

  37. Maybe I missed it, but what did the Weather Underground report for the 2:15PM September 8th, 2015 official temperature of San Francisco? Looks like they could have used 77 or 97 degrees – which did they use?
    The temperatures are “all over the map” between 77 and 97 for that afternoon.

  38. So what is the temperature variation between the top of the buildings and the ground? Can the shaded side of the top of the building provide cooler denser air which sinks along the face of the building into the warmer system close to the ground? An often used phenomena when sailing to use the katabatic winds off of hills near the shore line that provide more favorable winds. At the farm we know that cold air flows down off hills and forms pockets that are significantly colder and may harm fruit trees.

    • In the 1940’s my Grandfather would fire up the fans in the Citrus Orchard to keep the cold air pockets from forming.

  39. From what I can tell about reading Hadcrut, Berkeley Earth et. al. methodologies, they claim to be removing stations randomly and seeing if the final result changes. I’m not completely sure about this, the papers are a bit vague unless you are the one who wrote it (a common problem with all sorts of topics).
    However, the law of large numbers still applies. Yes, you will get bullcrap data for San Fransisco, because there’s not enough stations, but over the planet there are enough stations. The accuracy still increases by some constant (error bars for a single station) divided by the sqrt(N).
    My Monte Carlo analysis on auto-correlated surfaces show that constant is 2.5x that of the assumption of Gaussian uncorrelated noise in those papers. However, the e/sqrt(n) still applies. So given the fact there’s thousands of stations across the planet, they can still get more accuracy than you see in San Francisco.
    Don’t confuse the forest for the trees.
    Peter

  40. Well, whatever it is its hot. Working over in Alameda today right on the water where normally, it is quite shangra-la like. Not today. Never fear though global panickers, low 70’s by Saturday.

  41. Best way to get Mosher not to appear?
    Challenge him to appear.
    Very clever on your part.
    If I could answer for him he would say the UHI effect is already built in to compensate for city warming.
    And that it has no noticeable effect anyway.

  42. Several times I’ve observed “bubbles” of warm air moving along the surface and not immediately mixing with colder air. I felt this happen with a moderately strong wind pushing warm air over a cold lake and its a strange phenomenon to feel the air temperature change 10F-20F every 2 seconds. No gradual temperature gradient whatsoever, instantaneous changes. A similar thing can happens with water when warm river water enters a cold lake, sometimes there can be no gradual temperature gradient from warm water to cold, the warm water stays can stay intact and the temperature change from warm to cold can be instantaneous. Its strange to think of warm air/water and cold air/water behaving like oil and water and staying separate but it does happen. I would think when air is stagnant its also possible for “bubbles” of warm air to form and stay relatively intact with little to no mixing with surrounding cooler air, just an instantaneous temperature change when you move out of the warm air “bubble”.

  43. 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.

  44. “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.

  45. 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.

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