Another UHI effect – thunderstorms & lightning

The March-April edition of WeatherWise magazine has an interesting article in it regarding UHI (Urban Heat Island) effects of enhancing thunderstorm formation in the downwind heat plume. It Stems from this paper (PDF) published in the Bulletin of the American Meteorological Society. I saw a similar study presented in August 2007 when I attended Dr. Roger Pielke’s land use conference presented by Dr. William Cotton on the enhancements modeled in St. Louis, MO. Read that paper here

Radar reflectivity image of the March, 14, 2008 Atlanta, Georgia thunderstorm. Image from Weather Underground

Excerpts from WeatherWise Magazine:

The Atlanta Thunderstorm Effect

by Mace Bentley, Tony Stallins and Walker Ashley

Although nearly everyone is fascinated by lightning, some of us are terrified, while others are drawn to its elusive beauty. Lightning is one of the most photogenic of all atmospheric phenomena, but also one of the least understood. For all of its beauty, lightning is a major cause of weather-related deaths in the United States and accounts for more deaths than hurricanes and tornadoes combined. Nearly 40 percent of all lightning deaths occur when a person is involved in some form of outdoor recreation.

Now, new evidence suggests that lightning and its parent thunderstorms might actually be enhanced by cities. Urban areas are literally hotbeds for producing heat and lift, two important ingredients for thunderstorm formation. At the same time, throughout the world people are continuing to migrate to cities for employment opportunities and the search for a better life. Eighty percent of the U.S. population now lives in cities. City growth has increased the amount of urbanized land cover in the United States to nearly the size of Ohio! In the United States, many of our cities in the south are growing rapidly due to their location in a more temperate climate. However, a temperate climate also means cities are more prone to thunderstorms. Could all of these factors together combine to increase risk of lightning and other thunderstorm hazards to urban communities around the world?

The Urban Heat Island

The first step in unraveling the question is to understand the interaction between the land and atmosphere. It is currently thought that several processes in this complex interaction are likely at work in altering thunderstorm distributions around cities.

The first is the urban heat island effect, perhaps the most well-known atmospheric phenomenon produced by a city. An urban heat island occurs when the city registers higher temperatures than the surrounding rural areas. Cities heat up because of all the “activity” in them. Cars, air conditioning units, idling engines, and miles of asphalt and concrete all either produce or retain heat. The most notable feature of an urban heat island is the lack of cooling during late afternoon and evening after temperatures normally reach their highest. When compared to the rural countryside, urban corridors have much less area exposed to open air and instead have many warm buildings facing each other. Less heat is lost, and higher nighttime temperatures result. After sunset, city-to-countryside temperature differences grow quickly and can reach, in some cases, more than 10°F. The greatest city-to-countryside temperature differences occur during the long, hot days of summer when daylight is maximized.

Caption: Radar climatology illustrating the clustering of strong  thunderstorm days directly over and immediately surrounding Atlanta,  Georgia.

Caption: Radar climatology illustrating the clustering of strong thunderstorm days directly over and immediately surrounding Atlanta, Georgia.

Caption: Plot of lightning events during periods of westerly flow  illustrating downwind enhancement east of Atlanta, Georgia.

Caption: Plot of lightning events during periods of westerly flow illustrating downwind enhancement east of Atlanta, Georgia.

The Atlanta Case

The 10-year study of lightning, rainfall, and thunderstorm activity in Atlanta in the summer months showed that enhanced thunderstorm activity was found to shift due to prevailing winds. For example, westerly winds produced a distinct increase in lightning activity east of downtown Atlanta. Evidence suggests that thunderstorms developing over the city center, as well as storms along the periphery, were being directed by the westerly winds to the east side of the city and suburbs. The Atlanta enhancement, particularly for lightning, was well developed for westerly and northwesterly winds that carried thunderstorms east and southeast of downtown. Thunderstorm enhancement can occur in all directions around downtown Atlanta, directed primarily by the prevailing wind direction.

“Pollution can alter how a thunderstorm forms”

“As water droplets collide and freeze onto hail and other ice particles, negative charges are removed from the updraft and added to the downdraft of the thunderstorm”

The rainfall and lightning characteristics of thunderstorms developing in and around Atlanta were also detected when examining radar reflectivity. Over the 10-year study, high radar reflectivity “hotspots” were persistently found along and north of downtown Atlanta and immediately east of the central business district. Towering cumulonimbus clouds containing high concentrations of water droplets and ice crystals reflect significant amounts of microwave radiation back to the radar antenna. On weather radar displays, highly reflective areas are thunderstorms, which are typically color-coded in hot colors (i.e., reds, oranges) to make it easy to identify their size and location. Radar-identified thunderstorms were found to be greatest over the downtown with a general decrease moving outward from the city center. A similar pattern was found over other southern U.S. cities. It appears that the Atlanta urban heat island and associated buildings may combine to produce the downtown thunderstorm radar “hotspot,” while the urban heat island-produced circulations on the fringes of the city lead to increases in suburban thunderstorms, lightning, and rainfall.

“Radar-identified thunderstorms were found to be the greatest over the downtown”

Although less important, the terrain might also be linked to the lightning and rainfall patterns surrounding Atlanta. Winds from the northeast off the Appalachians and the focus of rainfall and lightning activity on the upwind side of Atlanta suggest that elevation changes across the metro area may interact with the urban heat island circulation and focus lightning and rainfall on the north side of the city. One explanation is that air flowing downhill from the Appalachians will be forced to rise once it encounters the buildings on the northern edge of Atlanta. This is distinct from other prevailing wind directions, where lightning activity was found to intensify over and downwind of the city center.

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Read the complete article at WeatherWise Magazine

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68 thoughts on “Another UHI effect – thunderstorms & lightning

  1. As far back as the 1960s, Tony Chandler gave his inaugural Professorial Lecture at the University of London on the London heat island. At much the same time, Bruce Atkinson, a geographer specialising in boundary layer climates, was discussing the effect of urban pavements on increased thunderstorm activity. I think some of this was published – I’ll see if I can track it down.

  2. Interesting. I’ve always felt that cities effect wind patterns as well. As the city of Sydney has grown, 7 miles from here, North East sea breezes have weakened, to the point that a strong NE sea breeze is rare here now. 15 miles further North they are unchanged. On the other side of the city they have strengthened. (I’ve been windsurfing for many years)

  3. Anthony,

    Seems like the UHI has alarmism in all sides. I wonder, when the cooling will REALLY begin in 5 years, if Al Gore will start talking about our “soot footprint” and how we cause Global Cooling. Like Al Gore doesn’t have enough money becuase of his fraud corruptions.

  4. Anthony,

    Another thing, Check THIS alarmist scream on http://www.global-warming.accuweather.com. You may want to check it out for your latest post.
    So much desinformation and distortion has been said above about what the article is really talking about.

    Go back in time, and you will find many papers stating what is the real impact from the solar activity fluctuation on earth temps and climate. No one is arguing there’s none, but it’s not that big and already accounted – it does’nt make a big difference on the outcome , it’s marginal.

    Answer to G. Karst:
    They are not trying to predict the next minimum. It’s not even about that. Your usual distortion to make a point.

    Answer to Dr. Science:
    Again, your out of the subject (the subject here is Solar Activity impact – not Al Gore). Your usual junk and vomitting about Al Gore. You have the right to say whatever you want about the guy, still do it at the right place and in the right subject. Usually Brett post something about him every three months – use that opportunity to bash all your soul, but please stay in the subject.

    Answer to Gary :
    They know about the other factors such as El Nino and others. They were looking for the impact of the sun activity fluctuation, and that’s what they are talking about. They are not predicting the climate, they’re saying the sun fluctuation will account for that amount of cool/warm output.

    To SVBOR :
    As usual, your linking a subject talking about the sun activity fluctuation with something else. At least you could have linked it to a paper saying otherwise. Always on the confusion, please spare us from what you see on your screen. I’m sure we can do better than that. And if you close your system, don’t look at the screen – the reflection is quite ugly.

    To Grumpy Old Man:
    Your twisting a little bit what they said. Short terms cycles cannot explain long term trends.
    Having said that, you’re also out of the subject. Of course, you have’nt found a response on the net for this story, so you have to come here with another one.

    TO FRANKOK:
    The image is from the same source many skeptical articles are using to say it is cooling because we’re (or were) in a solar minimum. No photoshop needed, it’s available online.

    To Paul:
    The pleasure you have in bashing Al Gore is your right, but this paper is not about him nor it is if the sun is heating or not the earth. It’s kind of obvious that if they are looking at the fluctuation of the sun, they are looking at what heat it does during the cycle. As i said to someone else, if you want to bash on Gore, choose the right subject.

    To The Wizard:
    The impact of the sun’s fluctuation is known and documented – going up or down it counts for about 13% of whatever warms this place. They are talking about ”FLUCTUATION” – not the all of the sun’s energy – only the fluctuation part. I know it’s confusing for someone who does’nt know the subject.

    To Stephan :
    That’s not what they said. But if it’s the way you understand things, i know why see the earth is flat and the sun is circling the earth everyday.

    To Anonymous, Oops, no it’s Robert :
    They got the data from the past, and they’re using models for what can be the future with multiple scenarios. They also challenges their models with the data from the past. What’s your point, they did exactly what you’re asking for, but it’s still not good for you. What do you want.. Ok i see, you needed to bash on someone even if you’re prooven wrong.

    To Sean2829:
    Who the hell told you that? Must be Joe. Still it’s not relevant to this subject.

    To MarkB :
    You got it (at last).. It should’nt be much of an influence as stated in the 2007 paper (more or less 6% of the raise and not a straight line – it’s a cycle).

    To Pete28 (again):
    You are wrong, climate’s prediction can already be challenge even if we’re not in 2100. If you choose the coolest of the scenario, currently we’re already above the predictable average. If you choose the warmest scenario, we’re quite short of it globally. So what you said is wrong and showing you don’t understand what GW theory is. Please read the report on the possible climate scenario on temps.

    To Oakden Wolf:
    Welcome in the club. You’re another one who is finding it is quite easy to debunk SVBOR with all the lies he’s always linking to. Have fun, you’re about to become the next name calling victim of M. Cut and Paste.

    To Caleb:
    El Nino has a large impact, but it is still a local one. At some places it’s not felt, and at others it’s about +8c. But more than that, El Nino is not alone. You got many oscillation playing with the weather and what you can feel and get at any place in the world. I don’t know anyone who claimed – and please go back to the archives – ”that the sun had no effect whatsoever”. What you’ve been told is that the impact was marginal and already accounted in the figures. Read the IPCC report, it’s there. The feedback from the sun’s fluctuation is about 6%.

    On the models, i agree with you, some are good – some are bad. But given the documented assumptions , show me where the climate models are wrong. You can still argue with the assumptions, but much less about the models.

    Derek Cummins : same argument as Caleb – same answer. You are twisting what has been said in the past. In fact what they are saying today is about the same thing as 10 years ago. The sun’s fluctuation has very little to do with the climate warming or cooling. The cycle is just to short to have an impact on climate. Still it can have an impact on the weather for a specific year. But don’t say it’s something new… It has been said over and over on this site, it’s written in the IPCC report, and written in numerous scientific paper for the past 150 years. Please come back with more accurate informations if you want to put a story.

    And you add : ”The sun is entering a long phase of being quiet, and as a result we can expect to cool for the next 30 years”. Where the hell are you coming from? The minimum is ending. We’re heading for the next maximum in about 3-5 years, and then it will start to go down. Don’t you know , it’s 11 years cycle. Just where do you get such stupid informations (i’m not calling you stupid, i’m saying that the arguments you copied is).

    Spring is here, snow is gone, flowers are emerging already.. About a month in advance, but SBVOR told me it was the ice age beginning.

  5. “On weather radar displays, highly reflective areas are thunderstorms, which are typically color-coded in hot colors (i.e., reds, oranges) to make it easy to identify their size and location”

    I believe the color coding is for temperature of the cloud tops, the “hot” reds really being colder cloud tops. The temps are used to determine the height of the cloud tops, higher being colder. I also seem to remember reading that clouds must grow to a height greater than 20,000 feet in order to produce lighting but I am not sure.

  6. Thunderstorms are weather events. Local influences as described by PielkeSr. are very real but are they altering the local climate through some local/regional weather patterns or the world climatic evolution?

  7. I think there are a lot of extra electrons left over from all those TV sets and they get together and draw the lightning.

    What? That’s at LEAST as good a theory as that global warming stuff!!!

  8. Not that many airports are being built these days, but this does suggest that commercial airports should be placed upwind from cities. DFW, for instance, is downwind from Ft. Worth, and has an interesting record of thunderstorms and microbursts.

  9. A recent example may have been the massive hailstorm a week or so ago in the Melbourne Suburbs – the massive hail storm (up to 100mm hail, smashing roofing tiles & car windscreens & panels) – The bad hail was some 30-40kms downwind from Melbourne CBD. Upwind & CBD areas received more “normal” hail (10mm)

    “Thousands of private cars were also pummeled, showing evidence of glass damage and dimpled panels over a wide area, from Nunawading to Belgrave in the Dandenong Ranges.”

  10. I had not considered the fact that urban heat would extend so far out into the surrounding countryside. Have any of the rural vs urban station analyses considered the impact of the direction of the rural station from the nearest large heat island? Based on that map above, it would appear to extend for a pretty good distance downwind.

  11. I had heard several years ago how the mega-city Tokyo generates thunderstorms. So basically they are now finding out that other large cities can do so as well.

    Love this bit:
    The first is the urban heat island effect, perhaps the most well-known atmospheric phenomenon produced by a city. An urban heat island occurs when the city registers higher temperatures than the surrounding rural areas.

    Jones, Hansen, Mann et al might have a slight objection to that statement. ;-)

  12. O/T It has been rumored that the Queensland Dept of Education (DET) has filtered out Watts and McIntyre’s Climate Audit, but kept in Real Climate and Deltoid.

    Winston Smith would be amused.

  13. One doesn’t have to live very long on the East Coast of Florida in order to observe this “phenomena” on a daily basis. The daily thunderstorm cycle in the warmer months offers a great insight as to the “Urban Effect” on local weather. I have actually seen clouds form and ascend from large parking lots as humid air races in from the West (interior) portions of the state. These clouds tend to form huge thunderstorms within 3-5 miles of the coast. This is where most of the urban effect is located. In areas where there is not a great degree of urbanization these storms usually form at or East of the coast itself.

  14. Interesting.

    When I lived in metro Atlanta for 20-odd years, I was quite familiar with a different effect. When a storm front with a line of thunderstorms would approach Atlanta from the west, they would die out as they hit the Atlanta UHI, then regenerate once they passed the metro area. But then I never really paid much attention to where thunderstorms bubbled up during an ordinary hot summer day, though it wouldn’t surprise me to see that the lift from the UHI would have an effect on storm location, intensity, and frequency.

    Since I was living on the western perimeter, it was quite frustrating during a hot, dry spell to see thunderstorms approach with much needed rain, only to see them dissipate short of Atlanta.

  15. I can testify as any other motorcycle rider can…Once your outside of the city limits and enter the rual area…temps drop dramatically..Especially in Spring and Fall…I was out today for the first time..I’m from the country and drove into a town…One can feel the difference…It was 67 today, full sun and no wind. Perfect day to ride!!!

  16. “Eighty percent of the U.S. population now lives in cities. ”

    I don’t know why,,, but I’ve never read that statistic before. I’m sitting here stunned! Must go look for my jaw! I think I may have kicked it under my desk somewhere. I feel foolish that I didn’t know this,,,,,,,,,,,,,,,

  17. Paul @ 15:28:19

    Greenhouse gas forcing fails cointegration with insolation forcing and temperature.
    ==============

  18. Very interesting. Hot air rises, collide with cooler air, add in some water vapor cussing rain which cools down the city. So If Co2 is causing the UHI, the result is rain cooling down the city or a Negative feed back to Co2 “heat effect”.

  19. Atlanta is also a MAJOR air hub. Jet exhaust is well known for its ability to seed unstable air and produce clouds and rain. No study of Atlanta weather can be complete without taking into account the jet activity around and especially downwind of the airport. Didn’t see any mention of that in the article.

    I work in a building that is under the approach to a major runway at YYZ. The area for several blocks gets more snow than adjacent areas. I’ve never been to a summer airshow in which it didn’t cloud up and spit some rain by late afternoon when there was a lot of low level jet demos.

  20. @Tom in Florida (15:36:14) :

    You said:

    ‘“On weather radar displays, highly reflective areas are thunderstorms, which are typically color-coded in hot colors (i.e., reds, oranges) to make it easy to identify their size and location”

    I believe the color coding is for temperature of the cloud tops, the “hot” reds really being colder cloud tops. The temps are used to determine the height of the cloud tops, higher being colder.’

    Not true. The color coding is given on the left hand side of the first image in the post and it relates to intensity of precipitation – higher dBz=more intense precipitation.

  21. From “killer Co2 domes” to “murderous UHI thunder & lightning effects.” Whatever next? The science is settled I tells ya.

    Seriously, the warmists will not pay any attention to this as it’s not caused by manmade Co2.

  22. Denny (16:39:18) :

    I’ll second that. In line with the article, the differences are far more noticeable at night. One thing that always gets me is how cold and warm pockets can be in depressions in the country. Being on the Plains, there are tons of them. It can drop 5-10 degrees in a very short span, then revert when you leave the low spot.

  23. Doesn’t the long post by Paul (15:28:19) : belong in a different thread? If he agrees it was mis-posted, I suggest that it be deleted.

  24. If 80% of the population is in the cities them so would the factories and employment. This would mean more electrical consumtion being drawn to the cities as well.

    Hmmmm.

  25. Ref – Hu Duck Xing (16:47:11) :
    “Eighty percent of the U.S. population now lives in cities. ”
    I don’t know why,,, but I’ve never read that statistic before. I’m sitting here stunned! Must go look for my jaw! I think I may have kicked it under my desk somewhere. I feel foolish that I didn’t know this,,,,,,,,,,,,,,,
    _________________________
    Believe nothing you read and only half of what you see. It really only looks that way at night from 45,000 feet. During the day it’s actually closer to 70%. But there too, you must realize that “cities” start at populations of 5,000 and go up from there:-) Americans just luv city-life. (Have no idea why.)

    Ref – Jimbo (17:24:09) :
    “From “killer Co2 domes” to “murderous UHI thunder & lightning effects.” Whatever next? The science is settled I tells ya.
    “Seriously, the warmists will not pay any attention to this as it’s not caused by manmade Co2.”
    ___________________________
    I hope you’re correct but I fear you’re not. Give Fat Albert and his gang half a fact and they’ll be out demanding another $450,391,759,975.98 Trillion to move all the city areas West of their current center line in order to avoid these “Mann-made” destructive effects of AGW. Shusssssssssh

  26. São Paulo Brazil is another city where you can see this effect. Before extensive urbanisation, the area was famous for “Manchester England” like drizzle. But now every afternoon during the summer enormous black clouds build up producing huge thunderstorms with torrential rain and flooding.

  27. Billy Liar (17:22:06) : “Not true. The color coding is given on the left hand side of the first image in the post and it relates to intensity of precipitation – higher dBz=more intense precipitation.”

    Of course you are correct. I should have been more specific as I was referring to the weather radar most of us get via our local forecasters, Accuweather and Intellicast.

  28. ” Billy Liar (17:22:06) :

    @Tom in Florida (15:36:14) :

    You said:

    ‘“On weather radar displays, highly reflective areas are thunderstorms, which are typically color-coded in hot colors (i.e., reds, oranges) to make it easy to identify their size and location”

    I believe the color coding is for temperature of the cloud tops, the “hot” reds really being colder cloud tops. The temps are used to determine the height of the cloud tops, higher being colder.’

    Not true. The color coding is given on the left hand side of the first image in the post and it relates to intensity of precipitation – higher dBz=more intense precipitation.”

    Still not right, quite. The colours signify the strength of the reflection of the radar off the density of water in the atmosphere – it need not signify precipitation, necessarily. The picture is of a classical thunderstorm, with leading edge notch (NE is front and the anvil end), and the direction of travel is SW to NE. At the back it has the telltale notch (SW, bottom side) of a weak echo region where the main updraft is going up. Looks like it might have another inflow jet on the other side, opposite. Look like there’s slight rotation to the updraft due to the high echo pattern near the inflows. Heaviest rain will be just SW of the highway “shield” near the center. The purple in the centre suggests there’s light to moderate hail up in the storm. Storm has well defined front and rear downdrafts, so there’s probably lots of wind coming out of it.

    The colours are not temperature based as they would be in an infared scan, but density based.

  29. The colours, btw, are entirely arbitrary. The NWS uses a defined set, but there are many variations in common use, and the colour table can be customised to enhance specific features. All the radar spits out is numbers.


  30. diane (15:55:00) :

    Not that many airports are being built these days, but this does suggest that commercial airports should be placed upwind from cities. DFW, for instance, is downwind from Ft. Worth, and has an interesting record of thunderstorms and microbursts.

    Take a look at the orientation of the majority of the runways at DFW; N-S.

    Ft. Worth is *west* of DFW and runways are laid out taking _prevailing_ winds into consideration …

    .
    .


  31. Tom in Florida (15:36:14) :

    “On weather radar displays, highly reflective areas are thunderstorms, which are typically color-coded in hot colors (i.e., reds, oranges) to make it easy to identify their size and location”

    I believe the color coding is for temperature of the cloud tops,

    Satellite, you’ re probably thinking satellite imagery, not the terrestrially-based NEXRAD WSR-88D RADAR which observes ‘things’ that an RF (radio) wave can reflect off of; this includes rain, drizzle, snow, birds, space-shuttle debris …

    .
    .

  32. An acquaintence of mine related that she had grown up in Montana. In her youth, dryland farming was the predominant land use pattern. As time passed, more irrigation was installed, so that eventually, almost all of the dry land farms were now irrigated.

    Afternoon thunderstorms, never present before irrigation, became a daily feature.

    The phenomenon might be related more closely to water vapor than UHI effects.

  33. What about tornadoes? I live just a few miles NE of Dayton, Ohio and many times in the summer big storms will form 10-15 miles east of Dayton(they don’t rain on me but I can watch them build if I look east southeast. Greene county, which is 10 miles east of Dayton, has more tornado reports than other counties around Dayton. The county seat of Greene county is Xenia, which had an F5 tornado in 1974 and an F4 about 10 years ago. Some people have looked at topography as a contributor, but I have never heard any suggest UHI from Dayton as a contributor. However, it would be consistent with this article about Atlanta.

  34. Jimbo (17:24:09) :

    Seriously, the warmists will not pay any attention to this as it’s not caused by manmade Co2.
    —————————–
    Yeah, well that’s why they just invented CO2 domes over cities, that takes care of the UHI and therefore the AGW is actually causing the thunder and lightning. Boo Hoo /sarc off/

  35. Up here in the Great White North, in the summertime, we are experience a phenomena they refer to as daytime heating, which causes thunderstorms to build in the late afternoon for a hour or two. The Calgary area is very dry (low humidity) and it doesn’t matter if the daytime temperature only reaches 60°F it’s still daytime heating. It happens on sunny days and somehow draws the moisture out of the ground to create thunder storms.

  36. People living in Moscow are used to strange winter lightnings over the city, which never appear in the surrounding rural areas. These “winter thunderstorms” started in 1980s, I think, and continue to this day.

    Moscow is drastically more built-up and densely populated than almost any other region in Russia. It certainly has it’s own micro-climate these days. Having a half-mad, half-drunk mayor who uses cloud seeding, artillery, and aviation in his (futile) attempts to control weather makes life in Moscow even more interesting. Not to mention the most nightmarish traffic on Earth; I’ve driven in New York, Montreal, London, and Athens — Moscow is worse!

  37. Isn’t this actually good news?
    I mean, for real environmental/civil engineers/scientists.

    Cities,at least coastal cities similar to Atlanta, cause rain? That’s great! Georgia is out of water, so Atlanta making rain is a good thing.

    With more studies, civil engineers can determine where best to put various types of drainage, collection and reservoir type systems.
    Environmental engineers,the sane ones, could determine basically the same thing. Perhaps including wetland/forest/’green zone’ development, preservation and things of that nature.

    With the extreme weather concerns, this is also good news. It can show the weather folks where to look and what to look for, giving higher quality advanced warning.

  38. This study ties in to the thermostat hypothesis http://wattsupwiththat.com/2009/06/14/the-thermostat-hypothesis/. One question – have any quantitative studies been done on the energy conversion of thunderstorms? If so, it should be possible to do an energy budget for urban heat islands and estimate the feedback effect.

    As a resident of Panama, we live smack in the middle of the tropical convergence zone. Although weather records are scarce (no government weather service to speak of), locals tell us that there is much more precip now than in the past, including as this year, in the “dry” season. 2008 brought 310 inches to our mountain community located right at the continental divide.

  39. I live in the I95 corridor in Virginia, just a couple miles west of the Richmond city limits. When I’m watching radars often I see storms coming from the West. Downsloping often makes them fade from view just to the west of the corridor a bit south of me, a few frames later just to the east of the actual line for I95 they pop up again.

    Really weird because it looks like the storms went underground then popped up through a hole by the side of the highway. I blame the trucks. ;)

  40. That is an interesting image of a thunderstorm. As an airline pilot flying in the tropical Asia, I see many many thunderstorms and our weather radars typically paint a completely different image to the one presented above. Especially when the precipitation is heavy our radars often suffer severe attenuation. It would be interesting to know how that image was actually formed.

    However, I have noticed how convective activity does tend to be present around the cities. Not so good for the airplanes wanting to arrive and depart said cities! But it has to be remembered that TS requires an unstable atmosphere, generally meaning that they will form, it is just a matter of where the first suitable trigger is that the unstable air comes across first. High ground, city or simply relatively hotter terrain compared to the sea.

    I can’t imagine that UHI will cause more TS, but may affect where TS will form depending primarily on the 2000′ wind direction. Outside of the tropics, I would imagine frontal weather would be the most common trigger. UHI would be way down the list.

  41. I live in Atlanta. Each thunderstorm season (as we call spring and summer around here), I watch Wunderground’s NexRad products with the glee of a child waiting for the next thunderstorm to roll in. I’m somewhat of an amateur severe storm buff you could say.

    I’ve also noticed on many occasions that lines of storms will break around the city perimeter as well as intensify. Many times I’ve watched severe lines that tracked for hundreds of miles simply fall apart around the city and then re-intensify when they’ve gone by.

    So yes, the heat island is there, although I don’t think we can say that it will intensify each storm that rolls through. I’d wager to guess that it’s probably about half.

  42. I realized recently that under the right conditions my own property appears to create a mini-UHI effect. I have a large shop, large house, and associated concrete shop apron and blacktop driveway, probably the largest combination of those for miles around in a sea of dark green forest. On certain cold, calm days a temperature inversion will exist, until a bubble of warm air near the surface bursts through the cold layer. When that happens the ravens detect it, their version of the “Surf’s up!” cry goes out, and they fly into it for a free ride up several thousand feet. When their lift in the bubble tops out, they do formation aerobatics and their grab-ass play on the way back down. By watching where they are circling and where they kick out of the bubble, you can see its location and height. For years I’ve enjoyed watching this directly overhead, and finally made the connection that it’s my own property which may be triggering the bubble to burst through the inversion. Now the question is how do the ravens find it — does one of them have to feel the lift by accidentally flying through it, or can they see an atmospheric optical disturbance caused by the warm air, or do they recognize the suite of conditions, including my mini-UHI, that will create it?


  43. Tony (07:05:27) :

    That is an interesting image of a thunderstorm. As an airline pilot flying in the tropical Asia, I see many many thunderstorms and our weather radars typically paint a completely different image to the one presented above. Especially when the precipitation is heavy our radars often suffer severe attenuation. It would be interesting to know how that image was actually formed.

    Tony, that RADAR image above is the kind of imagery that is rendered from data generated by the USA’s NEXRAD WSR-88D system.

    Basically, the NEXRAD WSR-88D uses an S-band frequency (2.7 to 3.0 GHz band and sometimes described as “10 cm” RADAR), a 28 foot dish which at S-band frequencies yields a beamwidth of under 1 degree with a corresponding gain of 45.5 dB. Maximum range is spec’d at 248 nm.

    The transmitter output stage musters 750,000 peak Watts, while average power works out to be only 1,560 Watts on account of the pulse width and duty cycle employed.

    ‘Rain’ penetration is superior to other RADAR bands normally employed for meteorological purposes (C-band and X-band) and is therefore desirable for the mission and desired accuracy of the WSR-88D RADAR. TV Stations employing their own weather RADAR usually employ a C-band model which for 1 degree angular resolution only requires a 14 foot dish antennna.

    The use of S-band for the WSR-88D results in reduced attenuation of both the initial incident RF ‘wave’ impinging on precip deep within a thunderstorm but *also* reduced attenuation of that back-scattered energy as it is reflected off the precip back to the RADAR site.

    Contrast this with airborne civilian ‘weather’ RADAR as used by the air transport professionals, an X-band (sometimes referred to as a 3 cm RADAR) which is much more attenuated by precip than C or S but results in a smaller dish thereby retaining some finer angular resolution. These beamwidth can be 3 and more degrees resolution but the overall size of the ‘dish’ is kept small (for aircraft nose-mounting installations).

    Nowadays, the FAA’s TDWR (Terminal Doppler Weather RADAR) are also available for RADAR weather imagery on the few dozen plus locale’s where they are installed; this is a C-band RADAR with less range (and half the dish size) than the WSR-88D as the TDWR fulfills a different mission than the WSR-88Ds.

    WSR-88D Quick specs: http://www.qsl.net/n9zia/pdf/wsr-88d.pdf

    Wx RADAR Wiki: http://en.wikipedia.org/wiki/Weather_radar

    Rockwell Collins: WXR-2100 commercial aircraft RADAR

    Rockwell Collins: User manual WXR-2100 including section on interpreting RADAR imagery for the WXR-2100

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  44. I’ve discussed this with other Naturalists in Texas.

    Our observations point to a collapsing of marginal surface based storms as they enter the UHI of Dallas-Fort Worth. My guess is that the humidity is less in the urban areas as there is less vegetation respiring to recharge the low-levels.

    On birds – and updrafts – they can feel it – just like ultra light or glider pilots can feel it.

  45. As a professional civil engineer (now retired), with a career as a transportation engineer, I am of the opinion that the UHI effect of asphalt concrete (AC) is significantly underestimated.

    This is somewhat of an extreme, but circa 1970, the temperature (in August, mid afternoon) of a recently constructed section of state highway near Tucson, AZ was measured by the state of AZ highway engineering department at 167 degrees F. Many municipal jurisdictions cover the AC streets every 5 or so years with a mixture of fine aggregate and asphalt, returning them to a very low albedo once again, so that is not so extreme a temperature after all, particularly in cities here in the southwest.

    Just got me a new toy a couple of days ago, a non-contact temperature measuring device, so just gave it a try. 2:00 PM here in Phoenix, AZ,
    March 18, 2010, air temperature (nearby weather station per Weather Underground) was 80 degrees F. Sidewalk (Portland cement concrete, PCC) was 110 degrees F. AC pavement (somewhat weathered) was 117 degrees F, and last years crack seal material was 121 degrees F.

    AC attains a significantly higher temperature in sunlight (thus storing lots more heat) than other construction materials commonly used. When the sun “goes down”, the AC continues to warm the much cooler air due to conduction (at the surface of the AC), and because of convection keeps warming new cooler air, and radiates IR to other structures in line of sight.

    For doubters, here is a great physical experiment to do this summer: At mid afternoon on a sunny day, just place your bare foot first on PCC curb/gutter or sidewalk, then place it on the AC pavement (you won’t be keeping your bare foot on the AC all that long, as it will be quite painful).

    Asphalt concrete combined with sunlight is the “gift” of heat that keeps on giving – long after sunset, as well as during daylight hours.

  46. I haven’t seen anything written up about it, but there’s another urban effect for towns on the Great Plains, including those along the Colorado Front Range. This area was virtually a desert when people first began living here. The only trees in Colorado Springs were those along the several ridgelines in town (almost exclusively evergreens) and cottonwoods and willows along the few year-round creeks. Today the city has more than two million trees, including a majority of deciduous varieties. Add in green lawns, and you have a serious increase in humidity – and moderation of temperatures – in the city and downwind. I’m sure the thunderstorm frequency on the plains east of Denver is also greater, with both a large urban heat-island effect and an increase in general moisture content of the ambient air.

    Jim – enjoyed your comment on RADAR. You are exactly right.


  47. Austin (11:32:50) :

    I’ve discussed this with other Naturalists in Texas.

    Our observations point to a collapsing of marginal surface based storms as they enter the UHI of Dallas-Fort Worth.

    That’s not really the sense we storm spotters who are often glued to RADAR and satellite imagery during thunderstorm events have. In fact, given the surface ‘flow’ of moisture from from the GOM (Gulf of Mexico) Ft Worth is less in that moisture flow than Dallas is (check a map, drop straight south from Ft. Worth).

    I have literally witnessed initiation of a ‘squall line’ late in the afternoon along the dryline along I-35E in Dallas. In fact, being a ‘naturalist’, you should note the change in plant life basically east of I-35 owing to increased seasonal rainfall amounts (this is also very apparent in which Corp of Engineers reservoirs take longer to fill up, etc, in the Ft. Worth area vs Dallas) … and becomes especially apparent by the time you reach east Texas …

    For this ‘sense’ you guys have, is it based on any observations (a time or two) … or more speculation? It would help to know, one could go back and look at other factors that may have intervened.

    Like – take into consideration meteorological factors such as powerful thunderstorm-inhibiting factors, like as measured by the CIN or CInh (Convective Inhibition) or more informally ‘the cap’ (the capping inversion); it is the primary factor that determines, 9.9 times out of 10, when and if we will have severe thunderstorm activity here in North Central Texas esp during the spring and summer thunderstorm season. The flow at this level is a little more variable than the boundary layer (which is predominantly S in spring/summer).

    THEN there is the location of the ‘jet’ or any other upper level low-pressure activity (SW trough, etc) that can influence T-storm initiation and progress and lifetime, before ‘cap’ effects begin to dominate, but I digress …

    See ‘cap': http://www.srh.noaa.gov/jetstream//append/glossary_c.htm

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  48. LarryOldtimer (15:07:08) :


    Just got me a new toy a couple of days ago, a non-contact temperature measuring device, so just gave it a try. 2:00 PM here in Phoenix, AZ,
    March 18, 2010, air temperature (nearby weather station per Weather Underground) was 80 degrees F. Sidewalk (Portland cement concrete, PCC) was 110 degrees F. AC pavement (somewhat weathered) was 117 degrees F, and last years crack seal material was 121 degrees F.

    Any compensation for (surface) emissivity (of the test subject)? That seems to be the biggest problem with non-contact thermal measurements; EVERYONE trusts that miraculous little digital display, whether or not it is anywhrere close!

    It would be nice to double-check those surfaces with a contact temperature measurement device, just to establish the correlation.

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  49. ” Tony (07:05:27) :

    That is an interesting image of a thunderstorm. As an airline pilot flying in the tropical Asia, I see many many thunderstorms and our weather radars typically paint a completely different image to the one presented above. Especially when the precipitation is heavy our radars often suffer severe attenuation. It would be interesting to know how that image was actually formed.”

    Tony, the additional information on the display indicates that the WSR88D is operating in VCP mode 212 (Volume coverage pattern 212). It doesn’t give you the specific nexrad product, but its most likely “base reflectivity .05&0176;” or, the lowest tilt, as this is the usual tilt for looking for low level tornados in reflectivity data.

    VCP 212 is a scan protocol that steps through 14 tilt angles (5 deg – 19.5) in 4 1/2 minutes. Its a fast scan used for rapidly evolving, widespread severe convective storms. Since it is likely .5 degree tilt, you’re looking at no more than about the first 10K feet of vertical storm (above ground). In this storm there is likely another 40Kfeet of stuff above! The pattern presented therefore represents the structure for only the lower part of the storm. In the 4 1/2 minute scan the radar is also doing doppler wind and outputting a bunch of derived products too, and the operator or data feed recipient can also step through the other tilts to see additional structure or visualize the storm in 3D. The pattern shown is characteristic of an HP supercell.

  50. An unemphasized aspect of this report is the value and quality of fieldwork in observation and analysis of real weather. This sort of work was the main driver of operational research through the first three-quarters of the 20th Century. In recent years much of the work has moved indoors to the laboratories of academic institutions where the understanding of weather relies on remote sensing, often retrospectively, and the modeling of weather systems from the macroscale through the mesoscale to the microscale has blurred the detailed and often chaotic character of actual weather systems to produce overly smoothed depictions so beloved by many modelers who use insufficient resolution to capture the fine details that could provide for more insightful hypothecation.

    On the subject of UHI effects on convective storm systems, field studies of these systems were carried out in great detail from the late 1940s and early 1950s. These studies were undertaken shortly after the end of WWII when radars became available for real time observations of such storms in three dimensions. Although such work is still going on today, namely at places like OU where storm chasing has been elevated to a genuinely academically involved study, it has not been as well supported by the percentage of funding being doled out to the meteorological research community that it commanded back in the good old days when field observations reigned supreme.

    A good example of the kind of work that was being done in those early days can be found in a comprehensive report on the activities of the Illinois Water Survey covering the latter half of the 20th Century. People like Stan Changnon, Floyd Huff, Dick Semonin, Ken Kunkel among many others, produced a stream of papers on the studies of weather and hydrology with emphasis on the impact to crops and local flooding. The report can found here. Note especially the extensive bibliography of the papers they authored including numerous studies of the UHI created by the city of St Louis and its effect on the inadvertent modification of convective storm systems over and downwind of the city. Much of this work was done between 1968 and 1979 with Changnon the lead author.

    The principal difference between their studies and a lot of the stuff that’s being done today was that the observational data came first. The theories and conclusions were derived after the data was collected and analyzed. Today we see many examples of the theories or more properly the hypotheses being determined in advance before a search was undertaken to find data to support them.

    For a near current illustration of all that is wrong with today’s climate science, it’s worth reading Steve McIntyre’s account of going to Colorado on a working vacation to actually drill a few cores from a grove of bristlecone pines where several trees had been used in paleometeorological studies and trying to get some of the actual dendroclimatologists from Boulder to take a couple of hours’ drive to join him in the effort. They wouldn’t leave the comfort of their ivory tower to take him up on that, even when Steve pointed out that there was a Starbucks within easy range of the groves in question. His reports can be found here.


  51. Austin (11:32:50) :


    My guess is that the humidity is less in the urban areas as there is less vegetation respiring to recharge the low-levels.

    Hi Austin, me again, on another point this time.

    Actually, I think the contrary is true –

    – we now have a) reservoirs and b) landscape/yard irrigation c) a lot of humans (they exhale CO2 and H2O) and d) a lots of hydro-carbon combustion (products of combustion CO2 and H2O)

    Also, our ‘flow’ is up from the GOM, so a _lot_ of what we generate locally is going to wind up downwind from us, which is going to be the Red River valley and into Oklahoma (speaking of the source as the Dallas area now).

    Current surface conditions … and on Friday they will indicate winds from the south for the Dallas area (given the prognostications)

    In fact, lets take a look at the Convective Outlook from by the SPC for Friday into Saturday here in NCTexas where they discuss moisture:

    DAY 2 CONVECTIVE OUTLOOK …
    1243 PM CDT THU MAR 18 2010

    AN UPPER-LEVEL TROUGH IS FORECAST TO DIG SEWD ACROSS THE FOUR CORNERS REGION FRIDAY AND INTO THE SRN ROCKIES FRIDAY NIGHT. AHEAD OF THE SYSTEM…A LOW-LEVEL JET WILL STRENGTHEN IN THE SRN PLAINS ALLOWING MOISTURE TO ADVECT NWD ACROSS CNTRL AND NORTH TX. BY FRIDAY AFTERNOON

    ALLOWING MOISTURE TO ADVECT NWD is the money quote, and that moisture comes from the Gulf on this occasion …

    Storm Prediction Center outlooks: http://www.spc.noaa.gov/products/outlook/

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  52. I couldn’t agree with this more (anecdotally speaking).

    I was stationed east of Cleveland at a Nike missile base HQ around 1970, back before the Clean Air & Water Act had a chance to have an effect.

    It was in the heart of an area called “The Snow Belt.” And the base was also on top of the highest land in the county, which contributed some cooling (and thus condensation was accentuated). But there was all kinds of pollution – especially as compared to today.

    The freaking rain storms were just ridiculous, filling up the wastewater ditches usually inside of five minutes. I still marvel at the downpours there, and just shake my head.

    It was explained to me by someone stationed with me about the weather coming across Lake Erie and the water condensing on particulates in the air from the heavy industry and the pre-catalytic converter cars. And I believed him; the evidence was right there. It was the only place in the US I’ve ever compared to monsoons.

    Yeah, it is one of those “Don’t you know the difference between weather and climate?” things, but I will forever remember the army buildings getting flooded as often as not. I have a hugely funny weather story about one of the dumbest Warrant Officers in the history of the world. Think Frank Burns… ROFL just thinking about him.

    Good memories!

    And all about rain.

    Oh, snow, too. SNOW. MANY intense, intense snowfalls there.

  53. This isn’t surprising. If you watch time-loop sat cloud views of the tropics, islands are preferred Tstorm locations compared to open ocean. This is because the land heats more than the ocean during the day, and a contrast is setup between the two. Such localized contrasts are what help Tstorms to develop. Night-time Tstorms can also develop just offshore of coasts or islands for the opposite reason — land cooling off more than the adjacent ocean during the night.

    A large city surrounded by cooler forest or farmland can be just like an island.

  54. Kind of continuing to demonstrate how ‘weather’ comes together across an area I am familiar with (the DFW area), here’s an excerpt from the Day 1 Convective Outlook from this morning:

    DAY 1 CONVECTIVE OUTLOOK …
    0722 AM CDT FRI MAR 19 2010

    VALID 191300Z – 201200Z …

    …TX/OK…
    A DEEP UPPER LOW/TROUGH IS SETTLING SOUTHEASTWARD
    ACROSS CA/NV…WHILE A STRONG COLD FRONT DRIVES SOUTHWARD ACROSS THE CENTRAL HIGH PLAINS THIS MORNING. INCREASING SOUTHERLY LOW LEVEL WINDS AHEAD OF THE UPPER TROUGH WILL TRANSPORT ONLY MARGINALLY MOIST AND UNSTABLE AIR NORTHWARD AHEAD OF THE FRONT…WITH ONLY LOW/MID 50S DEWPOINTS EXPECTED BY THIS EVENING OVER TX/OK.

    (Emphasis mine))

    And indeed winds are winding up a little with nice flow off the GOM and dew points in the upper 50’s (50 deg. F) just onshore in Texas and 40’s (40 deg. F) further into Texas and into Oklahoma:

    Surface obs Friday, 2-19-2010 1433 UTC (9:33 AM CDT) (This link is a ‘capture’ of the surface obs image from rap.ucar.edu/weather/surface and locked in time via an image saved on tinypic.com)

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  55. Continuing to look at the developing wx system … this is a fairly typical scenario setting up prior to a front coming through with warm, somewhat moist air coming off the Gulf (GOM); note that the wind has picked up quite noticeably from earlier (many of the wind ‘flags’ have 1 1/2 to two barbs showing – see the nice SE wind swoop off the Gulf then N into TX and OK):

    Surface obs Friday, 2-19-2010 2033 UTC (3:33 PM CDT) (Link goes to a ‘capture’ of the surface obs image from rap.ucar.edu/weather/surface locked in time via tinypic.com image)

    The meat of the size-up from the SPC (Storm Prediction Center) Day 1 Outlook:

    SEVERE THUNDERSTORM POTENTIAL WITH THIS SYSTEM REMAINS
    MARGINAL THRU THE FORECAST PERIOD…PRIMARILY DUE TO SUCH A MEAGER RETURN OF GULF MOISTURE IN THE WARM SECTOR.

    DEWPOINTS ONLY INTO THE LOW/MID 50S ARE ABOUT THE BEST THAT CAN BE EXPECTED SRN PLAINS PRIOR TO FROPA.

    HOWEVER A TYPICAL EARLY SPRINGTIME EML IS SPREADING EWD ACROSS THE SRN PLAINS AND COMBINED WITH SUFFICIENT HEATING SHOULD LEAD TO A REMOVAL OF MUCH OF THE CINH BY MID AFTERNOON. SURFACE BASED THUNDERSTORMS ARE EXPECTED TO DEVELOP AFTER 21Z ALONG AND JUST AHEAD OF THE SEWD MOVING COLD FRONT SWRN OK INTO NWRN TX.

    The “EARLY SPRINGTIME EML’ I had not seen before in Convective Outlooks, EML standing for “Elevated Mixed Layer”.

    For more on EML see: The Elevated Mixed Layer

    and

    A Synoptic Climatology of the Elevated Mixed-Layer Inversion over the Southern Great Plains in Spring. Part I: Structure, Dynamics, and Seasonal Evolution

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  56. And – to tie the ribbon on it … we today in N. Central Texas on Sunday the 21st of March have received approximately 4.5 inches of snow from the wx system that ultimately resulted from this southerly flow a day or so earlier … here is the unscientific snow measurement taken on the top of my car this AM:

    4.5 inch snowfall in Collin County (north of Dallas) 3-21-2010

    As we had gusty winds with this system, we had smallish drifts here and there, and initially a lot of the snow on concrete/road surfaces melt … snow depth on the sidewalk measured 1 inch, the road surface proper about 1/2 inch.
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