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-   -   The BA Cloud! (https://www.flyertalk.com/forum/british-airways-executive-club/1349294-ba-cloud.html)

BotB Jun 1, 2012 2:32 am


Originally Posted by Herman ze German (Post 18677871)

A nice day for a flight!

Okay, so I see two types of cloud here with an additional two features (and to help...both features are at the higher cloud level)...

Anyone care to take a guess at what two cloud types we have here? EDIT: ColdWalker has guessed one of them...some fair weather Cumulus...And the other type?

For bonus points: What subspecies of the higher cloud can be seen in the upper left corner?

And what Man made phenomenon (cloud) can we see in this picture?

I'll buy the person that guesses correctly a beer at the DO tomorrow or at the next opportunity!:)

ColdWalker Jun 1, 2012 2:37 am

Uhum BotB :


Originally Posted by ColdWalker (Post 18678055)
@herman ze German.

That is a very unusual picture! LHR with sunshine and fair weather Cu! To be specific cumulus flufia lamius if I'm am not mistaken ;)

That wasn't a guess. It was a reasoned scientific opinion!

To which I would like to add contrailius (Ct) and cirrus maximum upia (CsUp+)

Should one be using the F word (floccus) too ;)

BotB Jun 1, 2012 2:52 am


Originally Posted by ColdWalker (Post 18678083)
Uhum BotB :

That wasn't a guess. It was a reasoned scientific opinion!

:D



To which I would like to add contrailius (Ct) and cirrus maximum upia (CsUp+)

Should one be using the F word (floccus) too ;)
^ The crowd goes wild.... (and I owe you a drink!) ;)

So yes, Cumulus Fractus below (they are still looking a bit ragged as they have just started to form) and the upper level cloud is indeed Cirrus with some undulates showing at the upper left and indeed a few condensation trails forming Cirrus as well..(aka contrail).

Okay, now we need Herman ze German to bring in some German clouds for the advanced class...:D

Herman ze German Jun 1, 2012 3:06 am

We don't have Clouds in Germany, the Sun is always(!) shining :cool:

But to get us off-track a bit. The German News portal "Spiegel online" had an artivle about a Book from the British Cloud appreciation society (BotB, are you a member?) and had some rather impressive pictures http://www.spiegel.de/fotostrecke/wo...cke-82928.html
have a look at number 8 and find the 747

BotB Jun 1, 2012 3:41 am


Originally Posted by Herman ze German (Post 18678152)
We don't have Clouds in Germany, the Sun is always(!) shining :cool:

But to get us off-track a bit. The German News portal "Spiegel online" had an artivle about a Book from the British Cloud appreciation society (BotB, are you a member?) and had some rather impressive pictures http://www.spiegel.de/fotostrecke/wo...cke-82928.html
have a look at number 8 and find the 747

:) Well, it does shine more than in the UK...

Thanks for the link...I liked picture # 3 best...and not because of the broken heart! That picture shows some nice thunderstorm activity and Stratus forming below the main base of the storm...this occurs due to the precipitation that is falling causing the base of the cloud to lower or a new 'layer' of cloud to form where the air may already be saturated (if the air between the base of the cloud and the ground was not)...

:cool:

One thing that Germany does have is some extremes of weather...from the extreme humidity of Karlsruhe area...to the incredible rime icing that can occur on the Brocken, part of the Harz mountains...due to the combination of topography and abundance of moisture that are present...The weather can be more extreme here than in the many polar areas...

I've always wondered that any BA flights doing the run between the UK and D don't get more issues from winds/icing/storms when going to DUS or similar mid to lower regions...

Definitely a member of the Cloud Appreciation Society. Also a member of the Weather club and Royal Meteorological Society here in the UK...can recommend any of these to anyone interested in weather! ^

(or of course the equivalent society in most other countries...such as the DACH and associated Meteorologische Zeitschrift.)

BotB Jun 1, 2012 4:01 am

Seeing as we are celebrating all things British this weekend...

I am always amazed at the number of people that do not know about some of the great public resources available to them in this country...

For example: you can visit the UK Met Office Public Library and Archive free of charge and find one of the best libraries in the world relating to anything weather...there are also many historical weather items on display such as the first Beaufort Scale, one of the first weather charts (which we take for granted now but was classified as secret during the war for obvious reasons)...

So next time you are down Exeter way...do stop in and see some history! @:-)

henkybaby Jun 1, 2012 4:10 am

https://fbcdn-sphotos-a.akamaihd.net...03806406_n.jpg

The quoting became too complicated... :) To answer BotB's question where this was taken: Yellowstone Ntl Park. In May.

angeloedades Jun 11, 2012 3:38 am

It has been raining for 2 days non-stop now here in the Sydney CBD and I thought these were mean-looking clouds! :cool:

https://fbcdn-sphotos-a.akamaihd.net...20001199_n.jpg

https://fbcdn-sphotos-a.akamaihd.net...19839433_n.jpg

/AE

Moomba Jun 11, 2012 3:54 am

It has been raining for two years non stop in London. :mad:

henkybaby Jun 11, 2012 7:01 am

It is kind of nice here. No, no heavy aftereffects.

https://fbcdn-sphotos-a.akamaihd.net...24664384_n.jpg

Short Final Jun 11, 2012 7:26 am


Originally Posted by BotB (Post 18630650)
-Post detailed METAR or TAF (and any other relevant weather) information during periods of weather delays or interruption at an airport BA use in the hope it helps those travelling in their plans

Do we seriously want to waste space reposting TAF/METAR data that is easily and readily available elsewhere without any effort or registration required to gain access to it ?

Second, Meteorology For Pilots by Mike Wickson is the book to buy and read cover-to-cover if you want to understand the hows and whys of meteorology as it affects aviation and how to interpret the various forecast data. (ISBN 1840372842)

T8191 Jun 11, 2012 7:48 am

Possibly not, although some readers now have an idea how to decode a TAF/METAR. Fortunately I was trained to be able to do that.

But then we don't really need threads on Clouds, Trip Reports, discussion on champagne in the FLounge, Celebs on BA or advice on where to go on holiday.

What should we be discussing? I'm accused of posting drivel, so I shan't make any suggestions.

henkybaby Jun 11, 2012 7:58 am


Originally Posted by T8191 (Post 18735551)
What should we be discussing?

I believe the biggest killer on any forum is the meta discussion. Discussing the validity of a post, poster, topic or even the entire forum is a prayer without an end and should be avoided at all cost. Hence my conviction that the self appointed forum police (not the moderators) are creating more noise than they are preventing.

I do NOT believe Short Final is one of those by the way. I think his question was quite valid. I like clouds but I have no need for decoding the meteo-speak. If I want to understand that, I will buy the suggested book.

Ideally I want to post a picture of the evening sky and ask the experts if I need to bring my garden cushions inside. :)

T8191 Jun 11, 2012 8:04 am


Originally Posted by henkybaby (Post 18735613)
I believe the biggest killer on any forum is the meta discussion. Discussing the validity of a post, poster, topic or even the entire forum is a prayer without an end and should be avoided at all cost. Hence my conviction that the self appointed forum police (not the moderators) are creating more noise than they are preventing.

I do NOT believe Short Final is one of those by the way. I think his question was quite valid. I like clouds but I have no need for decoding the meteo-speak. If I want to understand that, I will by the suggested book.

Ideally I want to post a picture of the evening sky and ask the experts if I need to bring my garden cushions inside. :)

I concur, henky ... and my slightly piquant comment was certainly not aimed at Short Final.

The self-appointed Forum Police are a different matter.

henkybaby Jun 11, 2012 8:05 am


Originally Posted by T8191 (Post 18735648)
I concur, HIDDY ...

Quick! Change it before the mad expat finds out you think I am he!

:D :D :D

HIDDY Jun 11, 2012 8:09 am


Originally Posted by henkybaby (Post 18735320)
No, no heavy aftereffects.

Your photos are great henk but they always have a strange feel. Do you use an HD effect on them? It might just be the border which I think is ghastly. :p

henkybaby Jun 11, 2012 8:11 am


Originally Posted by HIDDY (Post 18735686)
Your photos are great henk but they always have a strange feel. Do you use an HD effect on them? It might just be the border which I think is ghastly. :p

They are shot on an iPhone with Pro HDR indeed. The edge is getting really old, really fast, I do admit. They work better on the black background on which they are normally used.

The 'strange feel' is what I am aiming for by the way. :D

T8191 Jun 11, 2012 8:11 am


Originally Posted by HIDDY (Post 18735686)
Your photos are great henk but they always have a strange feel. Do you use an HD effect on them? It might just be the border which I think is ghastly. :p

Broadly agree ... they would nice framed on a wall, but somehow the effect is too distorted.

Short Final Jun 11, 2012 8:54 am


Originally Posted by T8191 (Post 18735551)
Possibly not, although some readers now have an idea how to decode a TAF/METAR. Fortunately I was trained to be able to do that.

I was trained in that too.

However, there are many websites out there that will decode them for you (at least in a manner good enough for a non-pilot). So my point still stands. :D

Reminds me of a certain other forum I lurk on where if there's an incident, you're guaranteed to get some armchair investigator posting a TAF/METAR even if the weather is CAVOK with a mild breeze. Grrr.....


Originally Posted by T8191 (Post 18735551)
But then we don't really need threads on Clouds, Trip Reports, discussion on champagne in the FLounge, Celebs on BA or advice on where to go on holiday.

Indeed.


Originally Posted by T8191 (Post 18735551)
What should we be discussing? I'm accused of posting drivel, so I shan't make any suggestions.

The state of BA and its fleet, its place in the current marketplace. New routes. Useful tips & advice. All sorts... but anything other than the stuff you listed above.

T8191 Jun 11, 2012 9:02 am


Originally Posted by Short Final (Post 18735990)
The state of BA and its fleet, its place in the current marketplace. New routes. Useful tips & advice. All sorts... but anything other than the stuff you listed above.

With you up to that point! ;)

But from there on, is that really what FT is about? I thought it was Miles and Points? As to new BA routes, that's pure conjecture, isn't it?

Tips and advice ... Yes! But not apparently from Silvers and below, or those who fly less that n times a month :D

Fly safe ^

Stez Jun 15, 2012 11:09 am

From my TR,

This one is in east London somewhere around 9:45pm, I guess it is a broken nimbostratus and bits of altrostratus higher up maybe?

http://i.imgur.com/oMppul.jpg


Just starting approach to Singapore around 4pm, some hazy clouds and cumulus maturing?

http://i.imgur.com/tPNs8l.jpg

Aloxford Jun 15, 2012 1:31 pm


Originally Posted by T8191 (Post 18735551)
Possibly not, although some readers now have an idea how to decode a TAF/METAR. Fortunately I was trained to be able to do that.

I have no idea, I was not trained to do that, but its quite interesting to learn something new about the clouds one spends so long looking at


Originally Posted by T8191 (Post 18735551)
But then we don't really need threads on Clouds, Trip Reports, discussion on champagne in the FLounge, Celebs on BA or advice on where to go on holiday.

Yes we do!


Originally Posted by T8191 (Post 18735551)
What should we be discussing? I'm accused of posting drivel, so I shan't make any suggestions.

Anything and everything that is remotely relevant to travel on BA.

BotB Jun 15, 2012 6:03 pm

Sorry, been negligent in my duties...hadn't noticed the new posts as I've been busy doing the day job...:)

Down to it:


Originally Posted by angeloedades (Post 18734705)
It has been raining for 2 days non-stop now here in the Sydney CBD and I thought these were mean-looking clouds!

https://fbcdn-sphotos-a.akamaihd.net...20001199_n.jpg

https://fbcdn-sphotos-a.akamaihd.net...19839433_n.jpg

/AE

The first picture is of some Stratus that has formed below the base of the cloud that is providing the precipitation, the stratus appears quite well defined so the air below the main cloud deck is not as saturated although with time this will change if it continues and the two clouds can start to form together and join...

The second one is interesting but I can't tell what type unfortunately...nice picture though! ^ Can you provide any details of the weather during this time? Was there a warm front passing through? Is this photo very recent (last day or so? If so I can try to look at some satellite photos and come back on this...)

Thanks for posting! Hope the trip is going well...


Originally Posted by Moomba (Post 18734749)
It has been raining for two years non stop in London.

Certainly feels like, doesn't it :rolleyes:

Although we can use the moisture back in the UK soil, it would be better if it was more continuous and drizzle rather than convective showers.

Right now we are getting one system after another coming straight at us from across the Atlantic in what is known as zonal weather rather than meridional weather pattern...this is due to the fact that the typical Azores High has not built in as strong as it used to and therefore systems do not get weakened before they hit the UK and they do not have to travel up and over and then back down to the UK after weakening over colder water / land and losing energy...afraid it will be more of the same until we get a good blocking high pressure system in place...


Originally Posted by henkybaby (Post 18735320)
It is kind of nice here. No, no heavy aftereffects.

https://fbcdn-sphotos-a.akamaihd.net...24664384_n.jpg

Nice photo HB ^, some Altocumulus that has flattened and is becoming Altostratus as the vertical energy goes out of the air mass...see comment below about bringing the cushions in...:D


Originally Posted by Short Final (Post 18735433)
Do we seriously want to waste space reposting TAF/METAR data that is easily and readily available elsewhere without any effort or registration required to gain access to it ?

Second, Meteorology For Pilots by Mike Wickson is the book to buy and read cover-to-cover if you want to understand the hows and whys of meteorology as it affects aviation and how to interpret the various forecast data. (ISBN 1840372842)

Good to hear a different opinion and viewpoint. ^ Thanks for looking at the thread. I do hope that I am not just repeating a METAR or TAF without any further value...What I hope I have brought to the mix is some insight into why the TAF is calling for that weather and how the finer details of the TAF or METAR can help to interpret the situation (where it is causing a BA delay or issue)...see my posts up thread about the Jersey or Gatwick fog for example...I find a lot of the automated conversions for METAR or TAF fail at the important details and obviously don't give insight...Maybe this will change your mind about the value of them here...but I am happy to go with what others find of value and drop what they do not...please do remember that many reading the thread are not pilots or ATC controllers, etc...and may find the odd occasion of some info of interest and use. Hope this makes this thread more interesting.

Personally, any source, be it a book, website, video, etc...providing information that is useful to a person is good, so I am glad that you found that book of particular use. I am not familiar with it and will definitely have a look. ^


Originally Posted by henkybaby (Post 18735613)
<snip>...
Ideally I want to post a picture of the evening sky and ask the experts if I need to bring my garden cushions inside.

In the case of the above photo...No, you can leave the cushions outside :D


Originally Posted by Short Final (Post 18735990)
However, there are many websites out there that will decode them for you (at least in a manner good enough for a non-pilot). So my point still stands.

Reminds me of a certain other forum I lurk on where if there's an incident, you're guaranteed to get some armchair investigator posting a TAF/METAR even if the weather is CAVOK with a mild breeze. Grrr.....

Indeed.

The state of BA and its fleet, its place in the current marketplace. New routes. Useful tips & advice. All sorts... but anything other than the stuff you listed above.

Hope my above elaboration of why the TAF and METAR along with extra info may be of interest and use, however, as mentioned, if people don't find this of interest...I'll happily stop! :)

I'm a firm believer in trying to generate interest and foster knowledge...So if someone takes an interest in a weather event and asks I hope I can be of help.

I do believe the weather affects travelling and some BA operations here in the UK as well as enroute / outstations and for those interested in the best IFE going...I hope to help them tune into that channel and get more out of it ;)

At the end of the day, appreciate the feedback on this thread. We may have to agree to disagree...


Originally Posted by T8191 (Post 18736038)
Tips and advice ... Yes! But not apparently from Silvers and below, or those who fly less that n times a month

I disagree...Maybe the forum has a 'feeling' about it that stops Blue/Bronze/Silver people from posting about what they find of interest...but I do not see any guideline stating that they cannot post their thoughts and trip reports in World Traveller...I just think most posts are from those people that are willing to put finger to keyboard and express themselves...I hope we get a balance and have the spectrum available on here...I am sure things will swing back to 'normal' from the current F overdose...:)


Originally Posted by Stez (Post 18762317)
From my TR,

This one is in east London somewhere around 9:45pm, I guess it is a broken nimbostratus and bits of altrostratus higher up maybe?

http://i.imgur.com/oMppul.jpg


Just starting approach to Singapore around 4pm, some hazy clouds and cumulus maturing?

http://i.imgur.com/tPNs8l.jpg

Full marks for the first picture Altostratus call...however, the lower layer is Stratus that is turning into Stratocumulus, this lower layer is not very thick and you can see the 'rolls' (undulates) and ground between the breaks in the cloud...if it was Nimbostratus, you wouldn't and the Nimbostratus would extend from that lower layer all the way up to 10,000 feet or far higher... (think of Nimbostratus as a cube of fog that extends one or several Km in all directions...instead of a cloud that looks like a sausage like these ones do...) Good guesses though...you have the right 'type' of cloud, formed in stable air conditions...

The second photo is harder but a great photo ^

I believe we are seeing some ACC (or Altocumulus Castellanus) which is mid level turbulent clouds and some lower level Cumulus as well...the reduced visibility I believe is due to a large presence of particles for saturated air to 'wrap' around and start to form cloud...the conditions appear correct to form cloud but for some reason the cloud does not build uniformly in this photo...you see reductions to visibility because the light is being scattered away by these particles and does not reach your eye...in any case the 'haze' here is saturated conditions and plenty of CCN (Cloud Condensation Nuclei) allowing the start of cloud formation which reduces the visibility but as the conditions do not allow cloud growth everywhere we see some ACC forming in some places and only 'haze' in others...I expect that there is/was a high pressure that has been over the region for a few days or weeks and with all the particles in the air not being transported away and simply get trapped in this mid to upper levels until a new air mass comes in and 'cleans' the air out...There is some very good detail of the lower 'fibrous' cloud that develops into ACC as it hits a pocket of upward vertical potential and creates the well known bumpy cauliflower type heads (hence the castellanus term)...You can see this in the cloud in the middle of the picture on the left side (at the same position as the outer engine but on the left edge...where the cloud is darker and shears away, almost like a iceberg but in reverse...quite typical of ACC cloud...a clearer, less polluted photo of what you have here is:

Example of ACC developing


Originally Posted by Aloxford (Post 18763119)
I have no idea, I was not trained to do that, but its quite interesting to learn something new about the clouds one spends so long looking at

Yes we do!

Anything and everything that is remotely relevant to travel on BA.

Agree, and glad that you find this of interest.^

Sorry for the incredibly long post, hope the explanations are of interest.

BotB Jun 16, 2012 4:08 am

Lesson 3: Air Masses
 
http://farm9.staticflickr.com/8165/7...110698e4ee.jpg
The World is a Bunch of Bubbles by kind permission of NOAA, on Flickr

So, from previous posts we now know that we have weather because of temperature variations and the movement of that air to try to balance out the temperature which causes wind and modification of that parcel of air, causing cloud, precipitation, sunny weather, etc…we also know a bit more about the various clouds and if they are stable or unstable…but an important middle piece is missing…

Why is it that we get stable conditions and weather in some locations and unstable conditions in other areas…for example…the UK tended to get fairly moderate weather conditions year round whereas say in Florida you can get Hurricanes!…why? Shouldn't we just be one big air pocket that is colder at the top and warmer at the bottom and continuously mixing?

In a simplified world the answer is no. Although we have one atmosphere and of course all of this is mixing, we define the weather an area is experiencing by the air mass that happens to be over it at the time or by the weather that is between two air masses with different characteristics.

Starting with the UK, we are on an island and in a bit higher latitude…so our weather is typically quite moist (as we are surrounded by Ocean and have lots of moisture available…and the temperature is moderate…not too hot but not too cold either…this type of air mass (stereotyping now) is a 'm' for maritime, denoting the high moisture, and 'P' for Polar, again denoting the temperature, put together they give us the moisture and temperature characteristics of that air mass…so 'mP' means that the air typically is quite moist and moderate in temperature.

An air mass that we are talking about here is a large scale phenomenon…typically several hundred miles across and all the air in that 'bubble' has the same characteristics…so an air mass moving across the Atlantic towards the UK and Ireland will be uniform in moisture (as it is over the Ocean and is not being modified) and generally in temperature (if it is not moving North or South as well but rather mostly just at the same latitude…

This large mass of air defines the 'ability' of that air to produce weather and develop…as you can imagine…if the air is very warm and very moist…it can develop into much more dangerous weather than a cold and dry air mass (as there is little temperature difference between the bottom and top and little moisture for it to form cloud or precipitation…

A chap named Bergeron came up with a general air mass classification that we still use today (slightly modified) and helps us to understand what potential the air that is moving towards us is capable of and what weather will be associated with the transition zone between two air masses…

So, what do the letters stand for and why are they important: (using the first image above that is in the public domain and kindly provided by NOAA)

m = maritime (read moisture laden)
c = continental (read dry as over land so less moisture)

second letter describes temperature:

A = Arctic (or cold!)
P = Polar (or moderate temperatures)
T = Tropical (hot)
E = Equatorial (very hot)

There are others but these are the main culprits…

In addition: there are now a few other factors added to these descriptors...such as the stability of the airmass and (if known) how it is developing...Stable or Unstable are self explanatory...essentially giving some idea if this will develop Cumuloform cloud / Thunderstorms or not...(see the wiki article below for more info on this as well as identifiers for what attributes the air mass is taking on and modifying to...)

You can see an air mass called cA over the Arctic of North America and Greenland in the diagram…this air would be quite cold and have very little moisture…as cold air cannot hold much moisture, so typically would be very stable air and have very little 'weather' associated with it…this is why you do not generally get thunderstorms in the Arctic…and typically also get less turbulence over such regions (unless they are jet stream induced)…

Over the Equator, you see an mT air mass…this is a hot, very moist air mass that can produce strong thunderstorms, hail, turbulence, flooding, etc…as the only limitations are the air mass itself…it is not limited in growth by the amount of moisture available, nor by the temperature stopping the amount of moisture that it can hold…

Now, if the air was stationary this would be easy…we would know what weather to expect in each air mass…but as the air is constantly moving…the air masses change as they move over new ground…if the warm moist air mass moves over a cold winter landscape in continental Europe for example…it would cool down and lose its source of moisture (the Ocean) so would modify to become a cP air mass eventually…

On top of this situation, we have the transition zones between air masses…this relatively strong change over a short horizontal distance (around 1 to 10 miles wide) is the area where cold and warm air clash…and are what we call a 'weather front'….a cold front is the transition area where a cold air mass is advancing….a warm front is where a cold air mass is retreating…(for some reason we decided to always describe what the cold air is doing!)

two examples of air masses are below…(the 'bubble' of air over a flat ground surface being looked at from the side instead of from above as shown with the main NOAA image above)

http://farm9.staticflickr.com/8001/7...984dba59c7.jpg
mP air mass, 8 Km high by BA_pics, on Flickr

Here is a maritime Polar air mass (moderate in height, representing temperature potential and showing a cold front on the right hand side with a warm front on the left hand side)…guess what my next lesson will be! Fronts…even if they are not at the front of the queue….

Below is a representation of a mT air mass…much more vertical height to represent the increased temperature difference from hot below to cold up top…and smaller in horizontal size…typically mT weather is more convective...

http://farm6.staticflickr.com/5442/7...281fbe0a_m.jpg
mT air mass, 16 Km high by BA_pics, on Flickr

Cold fronts tend to be more defined and a much more abrupt transition between the air masses so the weather is also more dramatic…the warm front is more gradual and can be spread over 100 miles in some cases so the weather is more cloud and less showery precipitation…

The air masses tend to follow the wind patterns which in turn are based on temperature convection cycles that dominate at that latitude and also are influenced by the Ocean currents and temperatures of water and land…so depending on the season and surface beneath you, you will experience different patterns…around the UK we see generally a West to East movement and typically little strong deviation from the mP air masses…

However, as we have seen of late…we are starting to see more mT air masses coming to the UK and even some cA air masses in winter…giving us much more varied weather than we are used to…cold, snowy winter periods for several weeks and thunderstorms and heavy convective showery rain in Spring and Autumn…causing no end of frustration for BA as these unexpected changes in weather will affect how much staff they need, fuel to fly, airport movements, even down to how much and what we eat!

There is a good Wikipedia article on air masses here for those that want to explore this in more detail or for a better description of these main drivers of the weather you will receive anywhere…

http://en.wikipedia.org/wiki/Air_mass

Please also see this excellent post from simonrp84 showing a recent satellite image of the air masses EUMETSAT can now derive from the data they collect:

post116

that post shows the large scale the air masses cover and the variation of the air mass distribution around the world ^

Hope this helps you to understand the weather a bit better and also to try to identify the clouds you see and look for fronts when you are flying next time on BA! :)

Let me know if I have made a right pigs ear of this or if anyone has any questions...:)

T8191 Jun 16, 2012 11:36 am

You are doing an extraordinary job in informing us. I really do applaud that, most sincerely.
I doubt it would happen on the VS Forum :D

So, let me pose you a question. Not UK related, but around DC.

The forecasts in DC for Spring and Fall often/always flag up thunderstorms, usually in the afternoon. Sometimes they don't happen, sometimes they do … and they're very wet when it happens! Usually with an easterly flow as well, which I would have thought would have dumped any moisture through orographic lift as it crossed the Allegheny's.

To what extent, in your view, is this created by the vast expanses of tarmac/concrete generating thermal lift?
Put it another way … do big cities cause rain?

BotB Jun 16, 2012 12:47 pm

Thanks T8191, good to hear ^

To your question(s);

Do big cities cause rain: yes, in some situations.

Do large expanses of concrete cause rain on the city, as they soak up the heat...Not necessarily :confused:

So what am I on about?

The phenomenon is called an Urban Heat Island and is a relatively new field of study in the meteorological world...although it has been known about for some time...A quick Google search brought up some good hits if you are interested:

http://www.urbanheatislands.com/

http://science.nasa.gov/science-news.../essd16mar_1m/

http://en.wikipedia.org/wiki/Urban_heat_island

and an interesting one in case there are any teachers out there...

http://www.metlink.org/weather-clima...ackground.html

Interestingly enough, big cities definitely do cause what is known as a 'local' effect...due to the ability to soak up much more solar incoming radiation they heat up and cause their own heat release from combustion sources...they are a big heat sink and therefore do radiate heat up into the atmosphere which helps on one side to develop convective type clouds and systems in the right conditions BUT at the same time the extra heat (and lift) also mean that the cloud can develop but usually the precipitation is delayed until it passes the city...as the air can hold more moisture and therefore does not saturate and absorbs the moisture it tends not to rain over the city but then does cause heavier precipitation just afterwards when there is some cooling and subsidence of the air afterwards...

So, yes, the combinations of large amounts of moisture nearby, the strong Autumnal heating through relatively little pollution, the ability of the city to absorb that heat and 'fuel' the vertical development of the cloud...the easterly wind and storm track of the systems which delivers warm, moist air to the scene bring the right ingredients to the recipe and bakes a great storm...

Hope this is interesting and of use...

Interestingly, London doesn't seem to be too bad compared to the Eastern US for the urban heating...the large green parks, plenty of variety and water along with many other factors help to reduce the effect for our carrier of choice...

Continental Europe and the Eastern US are a completely different matter (which you can see from the thermal imaging on the above web pages...

T8191 Jun 16, 2012 12:52 pm

Thanks, BoT ... My morning reading, I think. What you have said vaguely conforms with my practical experience ... They warn about it , it looks serious, but then doesn't quite happen.

In fact, .... No, forget that.

HIDDY Jun 16, 2012 1:25 pm

More clouds from today and even a video. Although a lovely sky we have a very cold polar wind blowing here today BotB.

Video can be found here. I should warn you that you might feel a bit seasick watching it as the camera moves about a bit.....the cat clawing at my leg didn't help either.
To keep it on topic the BA flight to LHR can be seen in the far distance. ;)
http://i119.photobucket.com/albums/o...s/cloud166.jpg

45128 Jun 16, 2012 1:30 pm


Originally Posted by T8191 (Post 18767236)
You are doing an extraordinary job in informing us. I really do applaud that, most sincerely.
I doubt it would happen on the VS Forum :D

So, let me pose you a question. Not UK related, but around DC.

The forecasts in DC for Spring and Fall often/always flag up thunderstorms, usually in the afternoon. Sometimes they don't happen, sometimes they do … and they're very wet when it happens! Usually with an easterly flow as well, which I would have thought would have dumped any moisture through orographic lift as it crossed the Allegheny's.

To what extent, in your view, is this created by the vast expanses of tarmac/concrete generating thermal lift?
Put it another way … do big cities cause rain?

Problems at La Pouquelaye, T8191? :D

T8191 Jun 16, 2012 2:22 pm


Originally Posted by 45128 (Post 18767708)
Problems at La Pouquelaye, T8191? :D

I am locally rural, thank you.

Greater DC gets more rain than I do!

angeloedades Jun 17, 2012 3:55 am


Originally Posted by Moomba (Post 18734749)
It has been raining for two years non stop in London. :mad:

Haha! You haven't missed much here in SYD. It did remind me of London when it rained non stop! Thankfully its mild days this week around 18-25!

Having a wet look for my new job did not give the right impression on my first day!

/AE


Originally Posted by BotB (Post 18764351)
Sorry, been negligent in my duties...hadn't noticed the new posts as I've been busy doing the day job...:)

Down to it:

The first picture is of some Stratus that has formed below the base of the cloud that is providing the precipitation, the stratus appears quite well defined so the air below the main cloud deck is not as saturated although with time this will change if it continues and the two clouds can start to form together and join...

The second one is interesting but I can't tell what type unfortunately...nice picture though! ^ Can you provide any details of the weather during this time? Was there a warm front passing through? Is this photo very recent (last day or so? If so I can try to look at some satellite photos and come back on this...)

Thanks for posting! Hope the trip is going well...

Apologies for the very delayed reply. I have just started my new job and it is sucking my life away!

Very interesting indeed regarding the explanation above. They were very scary from my point of view... at one point in, the far distance it was started to swirl but it was just an illusion of a tornado! (I am not even sure if we get that here in Australia).

The pictures were taken on the day when it was uploaded but I think I might be too late for satellite images! Let me try and have a search from history records! My other half who is more versed at understanding the whether said that it was almost like two front's met that day. We did observe some wind changes but I could not tell you any more than that!

I have to say this thread is definitely keeping me busy at work! So much information! :D

Can we make this into a sticky?

/AE

BotB Jun 17, 2012 3:59 am


Originally Posted by HIDDY (Post 18767691)
More clouds from today and even a video. Although a lovely sky we have a very cold polar wind blowing here today BotB.

Video can be found here. I should warn you that you might feel a bit seasick watching it as the camera moves about a bit.....the cat clawing at my leg didn't help either.
To keep it on topic the BA flight to LHR can be seen in the far distance. ;)
http://i119.photobucket.com/albums/o...s/cloud166.jpg

;)

Nice Cirrus clouds there HIDDY, love the strong colour contrast of the white and blue...seems you are blessed with very little air pollution where you live.

Had a look at the forecast and satellite info...looks like this Cirrus is some higher spin off cloud from a weak weather front that is going over you right now...Nothing too serious though from the look of it.

Thanks for the video, looks like some lenticular clouds are also around (to the bottom and left side of the video when you are panning around...maybe this was just the way the Cirrus looked through that lens! Quite windy though!

Curious how the cloud developed today...

henkybaby Jun 17, 2012 4:05 am


Originally Posted by HIDDY (Post 18767691)
Video can be found here.

"So peaceful and quiet" I thought, until at 0:19 I discovered you live near a race track. Or what that the mrs Hiddy taking the tractor for a spin?

:D

BotB Jun 17, 2012 4:16 am


Originally Posted by angeloedades (Post 18770096)
Having a wet look for my new job did not give the right impression on my first day!

Apologies for the very delayed reply. I have just started my new job and it is sucking my life away!

Very interesting indeed regarding the explanation above. They were very scary from my point of view... at one point in, the far distance it was started to swirl but it was just an illusion of a tornado! (I am not even sure if we get that here in Australia).

The pictures were taken on the day when it was uploaded but I think I might be too late for satellite images! Let me try and have a search from history records! My other half who is more versed at understanding the whether said that it was almost like two front's met that day. We did observe some wind changes but I could not tell you any more than that!

I have to say this thread is definitely keeping me busy at work! So much information! :D

Can we make this into a sticky?

/AE

Hope the new job goes well, congrats! Make sure to take lots of cloud pics when travelling around and back to the UK ;)

Kind of you to ask about making this a sticky but I don't imagine it appeals to enough of the FT'ers to be that useful! ^ I'm hopeful that enough pics and posts will keep it in the first 7 pages in any case!

To your cloud photo and comments...


Originally Posted by angeloedades (Post 18734705)


Actually, this highlights an interesting point about how people describe weather...

From the pictures, and if I had no background info...I would say that this second photo especially is indeed quite threatening...and a convective type cloud coming from daytime heating (convection) or a cold frontal passage...however, when you said that it had been raining for two days straight...this would, on the face of it, indicate a warm front and stable cloud (as unless there were breaks in the rain, a convective cloud cannot rain that long)...so difficult to call this one. There are cases where two fronts meet (called an occluded front) which can indeed have prolonged rain and stable cloud but with some 'embedded' convective clouds such as towering Cumulus or Cumulonimbus...I'll try to have a look and see if I can get some satellite pics or weather data from then and come back to this but I do suspect the cloud you show here is a CB and the quite strange 'scoop' we see here is an 'outflow with some precipitation forming cloud as it is funnelled downwards...I can believe you that there may have been a funnel' cloud which is the start of a Tornado and occurs more than people realise...as long as it didn't touch down no worries...but not a good thing to fly through...regardless of size of aircraft!

This was why I asked about the second picture as it is a great photo and indicative of very serious downdrafts...I expect there were microbursts in that cloud...to have it embedded in a warm front would make it that much more dangerous as unless pilots know about this development they may not realise there is a CB hidden in there...Although the satellite and other data would show this at some stage.

^^

T8191 Jun 17, 2012 5:15 am


Originally Posted by BotB (Post 18767568)
Interestingly enough, big cities definitely do cause what is known as a 'local' effect...due to the ability to soak up much more solar incoming radiation they heat up and cause their own heat release from combustion sources...they are a big heat sink and therefore do radiate heat up into the atmosphere which helps on one side to develop convective type clouds and systems in the right conditions BUT at the same time the extra heat (and lift) also mean that the cloud can develop but usually the precipitation is delayed until it passes the city...as the air can hold more moisture and therefore does not saturate and absorbs the moisture it tends not to rain over the city but then does cause heavier precipitation just afterwards when there is some cooling and subsidence of the air afterwards...

Many thanks again … especially for all those links. ^

It now makes more sense, and sort of conforms with my observations - especially the precipitation being down-wind of the city. Taking a fairly typical air stream, it seems to rain more heavily to the northeast of DC [into Maryland] than it does where we go [southwest of DC].

simonrp84 Jun 17, 2012 5:52 am

To go back to the air mass talk from the previous page I thought that this might be of interest:
http://farm8.staticflickr.com/7102/7...67cf399c_c.jpg
A larger image is here: http://farm8.staticflickr.com/7102/7...7d5ef47e_o.png

It's a satellite-derived map of air mass that we produce, this image is from yesterday afternoon. The air mass types are the same as BotB mentioned and also included is an indicator of whether the air is stable or unstable. Because it's from satellite data the image isn't a direct measurement of air mass type - we can't get that information directly - but instead it uses some clever tests on the data we do have in order to derive an indirect 'guess' or the air mass type. In most conditions it does a pretty good job but occasionally it gets confused - a few times I've seen it conclude that air over the Sahara is polar, for instance.

BotB Jun 17, 2012 7:26 am

WOW...

Things have really moved on...brilliant ^ thanks simonrp84

I'll come back to this later this evening, really grateful you posted that ^

Right now I need to get out and enjoy the Sun with the other half or she will divorce me...:eek:

HIDDY Jun 17, 2012 8:04 am


Originally Posted by BotB (Post 18770105)
;)
Thanks for the video, looks like some lenticular clouds are also around (to the bottom and left side of the video when you are panning around...maybe this was just the way the Cirrus looked through that lens! Quite windy though!

Curious how the cloud developed today...

Thanks BotB...I was shooting into the direction of the sun which distorted the lens. The sky cleared not long after. Overcast today with a bit of rain.


Originally Posted by henkybaby (Post 18770120)
"So peaceful and quiet" I thought, until at 0:19 I discovered you live near a race track. Or what that the mrs Hiddy taking the tractor for a spin?

:D

No it was my 77 year old mother in law arriving on her new trail motorbike. She's been warned before about taking it out for a spin during siesta time.

BotB Jun 17, 2012 1:05 pm


Originally Posted by HIDDY (Post 18770754)
Thanks BotB...I was shooting into the direction of the sun which distorted the lens. The sky cleared not long after. Overcast today with a bit of rain.

No it was my 77 year old mother in law arriving on her new trail motorbike. She's been warned before about taking it out for a spin during siesta time.

Ah, was wondering if it was a scratch or water on the lens...still very good, thanks. ^

Saw that the forecast was calling for cloud but didn't see any precipitation being forecast...obviously developed more than they expected...

I can't believe no one has commented on your mother in law bit yet...Sounds like a scene from a movie :D Hope I am as fit at her age! ^

HIDDY Jun 17, 2012 1:17 pm


Originally Posted by BotB (Post 18772038)
Saw that the forecast was calling for cloud but didn't see any precipitation being forecast...obviously developed more than they expected...

A question BotB...I took a look at the Met offices satellite images for my area. It does show some cloud over the province but how do you tell if it's rain cloud or not? It's been constant moderate rain all day here yet the cloud shown looks quite thin.


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