A Walk In The Grass, on Cement, and Asphalt

Tonight I went for a short stroll outside. The sun was down hours ago as it is now about midnight.

As usual, I was barefoot. I spend as much time as possible unshod. (It’s a long story…)

This has given me ‘educated feet’. I grew up running from white paint stripe to grass patch on the mile walk to the city swimming pool. Shade was cherished. Black asphalt in the sun a known hell. Albedo education by contact…

Tonight I was reminded of that. A first step onto the walkway that had been shaded most of the day, but with some afternoon sun, was pleasant. Just a touch of warmth. A stray step to the side onto grass was cold and a surprise reminder to say on the path… Despite identical sun, the grass was cold, the path warm.

Stepping out into the street, the warmth was greater. Asphalt is like that. Walking in the dark about a block, I could tell were trees had shaded the road, and where it was sunny from both sides. Returning on the sidewalk, under trees the cement was nearly cold. (In a California way… just below room temperature ;-) Again stepping on grass was quite a bit colder. On the sidewalk, exiting from under a tree, the cement warmed. It had had the sun hours earlier.

So what did my feet tell me on this walk?

That the sun matters, a lot. What was warmest was what had the most sun.

That plants matter a lot more. Even in direct sun, grass stays relatively cool. Trees are known to let water out to keep their canopy at about 86 F (factoid remembered from some study on forest canopies with a PDF filed “somewhere” and done “sometime” for “someday” that ought to be today, but isn’t…) At night, plants cool very rapidly. They are water evaporators and water keeps them cool. Plants prevent heat storage as they shade the dirt keeping it cooler and evaporate ground water keeping the air cooler.

Cement, and more so, asphalt, matter as heat catchers, storers, and general warmers.

During the sun, pavement warms more. Plants are busy transpiring water and keeping air temperatures lower. As pavement warms, heat is conducted into the pavement. Then in the evening, when plants are quite cool, pavement radiates and conducts stored heat into the air for hours.

Anyplace that was mostly plants in 1900 would be much much colder than any airport today. Most of our present airports were grass fields then. Now they are pavement. Often with brown dirt as mowing costs more than spraying herbicide. The largest ones an ocean of cement. Not much water evaporating in the sun. Not many leaves shading the dirt. As night falls, foot thick runway cement slabs heating the air well into the night.

That, alone, ought to account for the “higher lows” seen in recent data. IIRC, it was something like 90% of GHCN thermometers were at airports now. All would have been grass in 1900. That ocean of cement can do nothing but raise night temperatures.

For thermometers near cities, the urban jungle is known to be a few degrees warmer. Ask any motorcycle rider… it gets darned cold when you leave town and enter the trees. Summers in California in the ’70s were spent on motorcycles. I would dread passing a peach orchard being irrigated at night. The air would be quite cold. Entering town, the warmth was welcome.

It seems such a simple thing. Grass, trees, cement, asphalt, bare feet and wind in the face. The water cycle cools. Plants cool. Country cools. Dry pavement warms, and keeps on warming into the dark. Cities warm. Asphalt heats a lot. (Ever walk on an asphalt shingle roof barefoot in summer sun? I have. I won’t again…) Cities are covered in asphalt, cement, pavement, roofing. So are airports. We put our thermometers of record in or near cities and airports. They simply can not report what it was like when all was green and evaporating water. We can not compare now to then.

Simply put, the land temperature record can say nothing about long term temperature trends without shouting about human development effects and massive heat islands. The Los Angeles basin is a metroplex that stretches for a few hours at 60 miles / hour. New York City surrounds central park on all sides. Chicago blends into suburbs of pavement and roofing for miles and miles. London… so many buildings and cars and pavement in such close contact. There simply isn’t a place to put a thermometer anywhere near those places that is ‘as it was’ 100 years ago. Or even 50 years ago.

Yet that is where temperatures were taken back then. In the little villages surrounded by nothing but plants and rivers for 100 miles. The giant city in the making but not made yet.

That is what my feet told me tonight. That try as we might, we cannot un-cement and un-pave and re-plant the miles of land around the first thermometer locations and get a reading that is fair to compare to the one from long long ago. That “global warming” is in fact very local warming in the heat (and pavement) islands around thermometers that are never placed where no people live, but mostly put at the concrete jungles of modern jet airports. Places where walking barefoot in the summer sun would be painful at best, but where winter snow is removed by force, chemicals, and jet exhaust. Places where laying on cool grass under a shady tree with a pick-nick basket can not be done. That “global warming” is in fact “local pavement warming”.


Best Answer: Millions of hectares of cropland in the industrial world have been paved over for roads and parking lots. Each U.S. car, for example, requires on average 0.07 hectares (0.18 acres) of paved land for roads and parking space. For every five cars added to the U.S. fleet, an area the size of a football field is covered with asphalt. More often than not, cropland is paved simply because the flat, well-drained soils that are well suited for farming are also ideal for building roads. Once paved, land is not easily reclaimed. As environmentalist Rupert Cutler once noted, “Asphalt is the land’s last crop.”

The United States, with its 214 million motor vehicles, has paved 6.3 million kilometers (3.9 million miles) of roads, enough to circle the Earth at the equator 157 times. In addition to roads, cars require parking space. Imagine a parking lot for 214 million cars and trucks. If that is too difficult, try visualizing a parking lot for 1,000 cars and then imagine what 214,000 of these would look like.

However we visualize it, the U.S. area devoted to roads and parking lots covers an estimated 16 million hectares (61,000 square miles), an expanse approaching the size of the 21 million hectares that U.S. farmers planted in wheat last year. But this paving of land in industrial countries is slowing as countries approach automobile saturation. In the United States, there are three vehicles for every four people. In Western Europe and Japan, there is typically one for every two people.

At 61,000 square miles, that is bigger than the state of Georgia but smaller than Wisconsin. If you took all the paved area and made it into it’s own state, it would rank 24th in area. Maine is ranked 39th at 35,385 square miles.

Now add in the area of airports, runways, taxiways, train tracks, and all those roofs… Think it is more than 2/300 ths? That’s 2 K out of about 300 K normal daytime temperature in absolute Kelvin. Somehow I think that matters; and might explain the divergence of satellite temperatures from the land (mostly at airports) temperatures.

Subscribe to feed


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...
This entry was posted in AGW and GIStemp Issues and tagged , , , , , , . Bookmark the permalink.

26 Responses to A Walk In The Grass, on Cement, and Asphalt

  1. Wayne Job says:

    One of the most sensible articles on global warming I have ever read. Thanks EM.

  2. Jason Calley says:

    Not only do plants keep the local air temperature down, but the moisture transpired into the air will eventually make its way higher, where the condensation can more effectively radiate heat into space. Toss in CO2 fertilization for increased plant growth and the net effect of CO2 may actually be cooling rather than warming.

  3. Ben Palmer says:

    “That “global warming” is in fact “local pavement warming””. Spot on! There can be no doubt that there is man-made warming, but not necessarily related to CO2. Not only pavement, but also all the heat emitted by motors, engines, refrigerators, heating, air conditioning in densely populated urban areas.

  4. philjourdan says:

    We should compare shoe stories sometime. I hate wearing them as well. And will only wear them in the extremes (snow and heat).

  5. menicholas says:

    Tony Heller just posted re a new NOAA “study”, released in Science, which completely erases any trace of the hiatus.
    Not only do they rely on their UHI contaminated surface data, while completely ignoring the high tech satellites, they have systematically and repeatedly altered the original data so thoroughly, it must now be regarded as worthless by any objective analysis.
    It seems all branches of government are now little more than paid shills for the political objectives of the White House.

  6. Larry Ledwick says:

    And thermal storage!
    Interesting that in the 1970’s the solar energy folks advocated “stone bin” heat storage. (actually a pretty good idea).
    You fill a large bin with fist sized rocks and pump the hot air from the solar collectors through the bin during the day, heating up the rocks. Then at night (much like a thick walled adobe home) those rocks can give back their heat to air circulated through the bin from the house at night. Stone and concrete make excellent thermal storage masses.

    As you mentioned due to evaporative cooling, soil does not get very hot, even when covered by sparse vegetation. It takes concrete or asphalt for the temperatures to reach egg cooking temperatures in direct sun.


    All those concrete structures become thermal mass flattening and delaying the evening cool down cycle.
    When I was young my father worked in a trucking company repair shop which had a huge concrete roof, that covered a couple of acres of shop space. In the summer that shop was an oven even late at night as that concrete roof radiated heat back into the shop space. In the winter, it became a refrigerator as the cold thermal mass of the roof after becoming cold soaked during a cold spell would keep the shop cold for several days after the temperatures moderated.

  7. nemesis says:

    Christopher Booker writes about UHI effect in this weeks Sunday Telegraph; http://www.telegraph.co.uk/comment/11718504/Mystery-grows-over-Met-Offices-hottest-day.html
    ‘No sooner had the BBC and all the usual suspects rushed to trumpet that last Wednesday was the hottest July day in the history of the world than more thoughtful observers, such as that diligent blogger Paul Homewood (on Notalotofpeopleknowthat), began raising their eyebrows.
    For a start, it was odd for the Met Office to base its claimed record of 36.7C (98F) on a single reading at Heathrow airport, when it is well-known that thermometers surrounded by a vast area of tarmac can exaggerate heat by as much as 2 degrees. Even the Met Office’s own hourly record only showed its highest Heathrow reading on Wednesday as 35.9C, while four other sites nearby showed the day’s hottest recording at just 35C……….’

  8. Gail Combs says:

    I had a similar experience this weekend.

    I was walking a circular route for about an hour in mid afternoon. Gravel to grass shaded by a building to a path through a manicured mature forest and back to the gravel. The grass was cooler than the gravel (also shaded) but the forest had a significant temperature drop. I wish I had a thermometer because it felt like a ~five degree drop.

    I have also had the occasion to lean against the inside of a horse trailer during a North Carolina summer. The white (primer) painted metal was warm. The dark blue metal would burn to the point of raising a welt.

    When living in South Carolina (1972 – 1975) I had to use gloves to keep from burning my hands on the steering wheel. In NC at least I do not have to wear gloves despite a black wheel in a black truck.

  9. Alan Poirier says:

    And even with all the UHI effect at work, we’re still cooling. We’re in for some rough times!

  10. DocMartyn says:

    The people here are deluded as Climate Scientists have debunked this ‘Urban Heat Effect’ and they KNOW that thermometers in the past were subject to MORE ‘Urban Heat Effect’ in the past record, than at present, which is why they are FORCED to cool previous temperature readings.

  11. Gail Combs says:

    What we do know is that the past 6 interglacials have lasted roughly half of a precession cycle, or currently 11,500 years. The Holocene interglacial is now 11,717 years old….. That’s two centuries or so beyond half the present precession cycle (or 23,000/2=11,500).The onset of the Little Ice Age was right about when the Holocene reached a half precession cycle old. Only one interglacial , MIS-11, since the Mid-Pleistocene Transition has lasted longer than about half a precession cycle.

    The Modern Warm Period, less warm then the the Medieval Warm Period, marks a second thermal pulse (warm period). There were two thermal pulses in the closest Holocene analog, MIS-11 just before glaciation. The Milankovitch Cycle low point will continue for 65 thousand years according to Lisiecki and Raymo. Yet these idiots in DC and in the UN want to strip the earth of the CO2 security blanket that might be keeping us out of the next ice age. And to add insult to injury you can add the other papers showing C3 plants (99% of the plant species) were undergoing CO2 starvation when the earth was in the last glaciation.

    …the June 21 insolation minimum at 65N during MIS 11 is only 489 W/m2, much less pronounced than the present minimum of 474 W/m2. In addition, current insolation values are not predicted to return to the high values of late MIS 11 for another 65 kyr. We propose that this effectively precludes a ‘double precession-cycle’ interglacial [e.g., Raymo, 1997] in the Holocene without human influence….

    Click to access Lisiecki_Raymo_2005_Pal.pdf

    From what I can piece together we are at the transition point in terms of 65° N June insolation.

    A paper from the fall of 2012 Can we predict the duration of an interglacial? gives the calculated solar insolation values @ 65° N on June 22 for several glacial inceptions:

    Current value – insolation = 479W m−2 (from that paper)

    MIS 7e – insolation = 463 W m−2,
    MIS 11c – insolation = 466 W m−2,
    MIS 13a – insolation = 500 W m−2,
    MIS 15a – insolation = 480 W m−2,
    MIS 17 – insolation = 477 W m−2

    Solar insolation isn’t a cut and dried measure for glacial inception. Steve Goddard (Tony Heller) BTW thinks the Holocene will go long. Autumn and winter are occur at the closest approach of the earth to the sun for the northern hemisphere, the earth is moving at its maximum velocity and autumn and winter are shorter than spring and summer. This is the reason for the debate about MIS11..

    So where are we in terms of the Milankovitch cycle and solar insolation?

    NOAA: @ 60° N (not 65° N) in June

    Holocene peak insolation: 523 Wm-2
    ……………………………………………..decrease = 47 Wm-2
    NOW (modern Warm Period) 476 Wm-2
    …………………………………………….. decrease = 12 Wm-2
    Depth of the last ice age – around 464 Wm−2

    It is interesting to note that the solar insolation had to be near peak to kick the earth out of the Wisconsin Ice age.
    11,000 years ago…………… 523.16 Wm-2 peak insolation
    Wisconsin Ice age===> Holocene transition
    12,000 years ago…………… 522.50 Wm-2

    To me that suggest that once the earth goes solidly over the ‘tipping point’ in to glaciation for what ever reason, there is no going back.

    The two questions I have are:

    1. If we pump out enough CO2 into the atmosphere will it be enough to keep the earth from massive cooling? Even during the time between the two precession cycle peaks in MIS11 the temperature was darn cold, wild and nasty. (Think Little Ice Age or worse.)

    2. Do the Elite actually believe we are headed into either Little Ice Age conditions or worse. Are we being Grubered so they and their descendants can survive while we die? Is that why the emphasis on population control started in the 1970s at the same time Hays and Shackleton proved the Milancovitch theory with hard data from sea bed cores?

  12. Paul, Somerset says:

    In the UK the effect is most noticeable for rural dwellers in winter. I regularly cycle a couple of miles through the countryside on frosty mornings, my hands frozen despite gloves. Yet the moment I turn from a country lane bordered by hedgerow and fields onto a road with sidewalks and a few houses I can suddenly feel my hands again and the sensation of a blast of “warm” air against my face.

    It’s unfortunate that so very few of us ever now travel into and out of rural areas in any other way than inside a motor car. Certainly nobody who truly believes in global warming has ever tried it.

  13. Larry Ledwick says:

    For the last several years I have had a digital car thermometer located where I can easily see the digits as I drive. I work the swing shift getting off work well after sunset, near 10:00-11:00 pm. I can see the effect of UHI as I drive (and micro climates due to other effects like cool river valleys). I can see temperature changes of 2-3 degrees in a mile transitioning from open pasture tree bordered roads into residential and commercial neighborhoods. The transitions are consistent and repeatable night after night if winds are light. Stronger breezes blur the transitions significantly.

  14. craigm350 says:

    Reblogged this on the WeatherAction News Blog and commented:
    UHI explained in simple terms that even the Met Office could understand. ;)

  15. Clay Marley says:

    Here in Phoenix AZ we have low water landscaping, but most everyone has a patch of grass in the back yard. Good for the kids and pets to play on and to do their business on (the pets that is).

    Most people have real grass, but some like to install artificial plastic grass. Low maintenance and looks good, if not too good. I took care of a friend’s yard last summer while she was traveling. When I reached down to clean some debris off her artificial “lawn” I was stunned at how hot it was. No way I could walk on it barefoot and I’d never let a pet walk on it. The plastic grass was much hotter than the concrete patio.

    Until then I had never thought about how cool real grass is even on a hot Phoenix summer day.

  16. sabretoothed says:

    First its not warming, then the NOAA adjusts the temperature so that its actually warming again.

    That makes these studies look stupid, as first there was a pause, and these studies tried to justify it, then NOAA made is warming again, so the 2 below studies look ridiculous now



  17. UHI has always been grossly underestimated.

  18. Gail Combs says:

    Clay Marley says: “… I took care of a friend’s yard last summer while she was traveling. When I reached down to clean some debris off her artificial “lawn” I was stunned at how hot it was. No way I could walk on it barefoot and I’d never let a pet walk on it. The plastic grass was much hotter than the concrete patio….”

    A SWAG: White (concrete) reflects most colors while ‘green’ only reflects green light. That means anything green colored (or any other color) will be hotter.

    (If I am wrong guys let me know.)

  19. Gail Combs says:

    Alan Poirier says: “And even with all the UHI effect at work, we’re still cooling….”

    It is even worse than you think.
    Zeke Hausfeather states in Understanding Adjustments to Temperature Data.:

    …… Most of the stations have changed from using liquid in glass thermometers (LiG) in Stevenson screens to electronic Minimum Maximum Temperature Systems (MMTS) or Automated Surface Observing Systems (ASOS). Observation times have shifted from afternoon to morning at most stations since 1960, as part of an effort by the National Weather Service to improve precipitation measurements.

    All of these changes introduce (non-random) systemic biases into the network. For example, MMTS sensors tend to read maximum daily temperatures about 0.5 C colder than LiG thermometers at the same location. There is a very obvious cooling bias in the record associated with the conversion of most co-op stations from LiG to MMTS in the 1980s, and even folks deeply skeptical of the temperature network like Anthony Watts and his coauthors add an explicit correction for this in their paper…..

    Instructions were written and given out to the observers in 1882. There were two thermometers, one max and one min.

    For the maximum thermometer they state:
    “…When a maximum thermometer is not read for several hours after the highest temperature has occurred and the air in the meantime has cooled down 15° or 20°, the highest temperature indicated by the top of the detached thread of mercury may be too low by half a degree from the contraction of the thread….”

    That would indicate the max thermometer should be read just after the heat of the day and any adjustment for reading at the wrong time of day should RAISE the maximum temperature not lower it!

    But it gets worse….

    The last couple of days I posted on an 8.5 year side-by-side test conducted by German veteran meteorologist Klaus Hager, see here and here. The test compared traditional glass mercury thermometer measurement stations to the new electronic measurement system, whose implementation began at Germany’s approximately 2000 surface stations in 1985 and concluded around 2000.

    Hager’s test results showed that on average the new electronic measurement system produced warmer temperature readings: a whopping mean of 0.93°C warmer. The question is: Is this detectable in Germany’s temperature dataset? Do we see a temperature jump during the time the new “warmer” system was put into operation (1985 – 2000)? The answer is: absolutely!

    So just between the TOBS change and the change to the new electronic measurement system you are looking at about 1.5°C or more before you get to thermometer placement — Frank Lanser’s “Original Temperature Project” (coastal vs inland) and the “march of the thermometers” (see WUWT)

    The surface temperature record is now so screwed up it is impossible to actually tell what is happening. Unfortunately the satellite record starts in 1979 many years too late to catch the high temperatures in the 1930s.

    Of course you need temperature plus water vapor to have any real idea of what is happening to the atmospheric energy budget.

    What is really funny is thanks to the energy bound in the heat of vaporization, if the water vapor goes up, as demanded by the CO2 global warming conjecture, the world temperature should actually be go DOWN!!!! (And the deserts should be contracting)

    For example look at the humid Brazilian rain forest, Barcelos, Brazil, and the dry N. African Desert, Adrar, Algeria.

    This data is from May (2012) which is midway between the vernal equinox and the summer solstice and therefore the sun would be midway between the equator and the Tropic of Cancer (the latitude line at 23.5° North) so the solar insolation at both locations would be roughly equal with a bit more expected in Barcelos, Brazil.

    Barcelos, Brazil
    ….monthly min 20C, monthly max 33C, monthly average 26C
    Average humidity 90%

    Adrar, Algeria
    …..monthly min 9C monthly max 44C, monthly average 30C
    Average humidity around 0%

    The effect of the addition of water vapor (~ 4%) is not to raise the temperature but to even the temperature out. The monthly high is 10C lower and the monthly low is ~ 10C higher when the GHG H2O is added to the atmosphere in this example. The average temperature is about 4C lower in Brazil despite the fact Algeria is further north above the tropic of Cancer. Some of the difference is from the effect of clouds/albedo but the dramatic effect on the temperature extremes is also from the humidity.

    I took a rough look at the data from Brazil. Twelve days were sunny. I had to toss the data for two days because it was bogus. The average humidity was 80% for those ten days. The high was 32 with a range of 1.7C and the low was 22.7C with a range of 2.8C. Given the small range in values over the month the data is probably a pretty good estimate for the effects of humidity only.

    You still get the day-night variation of ~ 10C with a high humidity vs a day-night variation of 35C without and the average temp is STILL going to be lower when the humidity is high and the effect of clouds is removed.
    DATA from: classic(DOT)wunderground.com/history/station/82113/2012/5/22/MonthlyHistory.html

    This data would indicate GHGs have two effects. One is to even out the temperature and the second is to act as a “coolant” at least if the GHG is H2O, the most significant GHG.

  20. Larry Ledwick says:

    Solar collector designers experimented with different colors for the absorber and a dark green can be very nearly as good at black for thermal solar collector. It is a question of the surfaces absorption and emittance. You can have coatings which absorb efficiently at the common solar illumination frequencies but radiate very poorly at the infrared frequencies. These selective coatings can dramatically change the final temperature of a surface exposed to the sun.

    I accidentally discovered how this works back in the 1960’s while working on a car. It was a blistering hot day, in direct sun and I had several tools laying on the concrete beside me. The dark rust colored and black oxide coated tools were not the hottest tools. They were hot and uncomfortable to pickup, but the shiny chrome plated wrenches were so hot that they would burn you. I had to pick them up with a rag and drop them in a bucket of water to cool them enough to hold them in my hand. The chrome coating acted as a selective coating, it did not absorb a lot of solar energy but it had very low emissivity in the infra red and ultimately reached a higher equilibrium temperature. Infra red emissivity is not at all related to visual color of an object.

  21. J Martin says:

    To answer Gail’s question 1. We had a glaciation with 4000ppm co2 ten times as much as we have now, at the end of the Ordovician and through the Silurian periods.

  22. Gail Combs says:

    Thanks J Martin,

    Actually the first question was a shut-up for the chicken littles. (I have never seen them answer it.)

    If you think CO2 causes warming why ever would you remove it at the tail end of an interglacial when the solar insolation (June @ 65°N) has dropped 47 Wm-2 from the high needed to thaw out the earth and is now near the ‘tipping point’ into glaciation? This ‘tipping point’ is somewhere between 463 W m−2 and 500 W m−2.

    MIS 11 is a possible analog for the present interglacial and the ‘tipping point’ was 489 W m−2. That is 15 W m−2 HIGHER than the present minimum of 474 W m−2. [Lisiecki & Raymo, 2005]

    The ClimAstrologists are saying that the CO2 forcing is not only going to keep the earth out of glaciation buy also going to make it warm catastrophically. The entire CO2 forcing is 32 to 44 W m–2 [cf., Reid, 1997]. and all but 5 to 6 W m–2 of that forcing occurs in the first 200 ppm CO2 (modtran, see below) so the earth is STILL 10 W m–2 short of safety even by their numbers and because CO2 forcing is logarithmic it is going to take a lot more CO2 to get to ‘safety’ some where well over 1500 ppm the amount I would like to see in the atmosphere.

    That is all using THEIR numbers!

    There are even papers that cover this point.
    Lesson from the past: present insolation minimum holds potential for glacial inception

    ….Because the intensities of the 397 ka BP and present insolation minima are very similar, we conclude that under natural boundary conditions the present insolation minimum holds the potential to terminate the Holocene interglacial. Our findings support the Ruddiman hypothesis [Ruddiman, W., 2003. The Anthropogenic Greenhouse Era began thousands of years ago. Climate Change 61, 261–293], which proposes that early anthropogenic greenhouse gas emission prevented the inception of a glacial that would otherwise already have started….

    Ruddiman’s “early anthropocene” hypothesis says human-induced changes in greenhouse gases did not begin in the eighteenth century but 8,000 years ago with the intense farming activities of humans. This stopped the overdue-glaciation.

    If anything has caused a ‘delay’ I am more inclined to think the major impact is cities, deforestation, farming and plowed earth in the spring changing the amount of solar radiation held by the earth surface. However the Modern Grand Solar Maximum is more likely.

  23. cdquarles says:

    @ Gail,

    If I am remembering my astronomy correctly, the solar mid-point between the equator (roughly 11.72 degrees, since the current obliquity is about 23.44 degrees) and the Tropic line should be about 4 weeks into Spring/Fall, or mid-April for the Northern hemisphere and mid-October for the Southern. From memory at my latitude, solar Zenith reaches 70 degrees in April and stays above that until August. For zenith angles above 60 degrees, we see that one week into spring (March) and it stays there until one week before autumn (September). Mid-May zenith angles, for me, are about 77 degrees, reaching a bit over 80 at the solstice.

  24. Gail Combs says:

    cdquarles, It might be worth looking at the data for April 2012 to see if there is any real difference in the analysis.

    I will try to do it if I get a chance but Wunderground has changed the format and no doubt changed the temperatures as well. (Rolls eyes)

Comments are closed.