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Weather => Forecasting => Topic started by: Hugh Westacott on August 05, 2012, 04:01:54 PM

Title: Cloud movement and direction
Post by: Hugh Westacott on August 05, 2012, 04:01:54 PM
The movement of clouds is sometimes different from wind direction. Does anyone know of a technique that can be used by walkers to establish, with reasonable accuracy, the direction in which clouds are moving?

I've tried tracking cloud movement along the direction of travel line on the mirror of my Suunto MC-2 , but it's not easy because the mirror is too small to be accurate.

Hugh
Title: Re: Cloud movement and direction
Post by: adi on August 05, 2012, 06:10:28 PM
Let me clarify something, clouds always travel in the direction of the wind at the height of the cloud which may be different to that at ground level.

When weather observations are made the wind is measured at a height of 10 meters above ground level this is to help to eliminate friction with the ground and micro climates that both effect the measurements.

How complicated do you want me to answer this? Basically when you have a weather forecast it is based on sea level where ever on the planet you are although now a days the Met Office do forecast for the average height of an area. So on Cairngorm you are going to get a more average forecast for the height than that at sea level.

When wind blows in a different direction at altitude than that at ground level is known as shear or more precisely vertical shear. Most upper level clouds are driven by what is known as the jet stream, as are low pressure systems and cumulonimbus. The jet stream brings our weather to our shores but has little effect on how the wind moves around obstacles on the ground such as building, mountains and the list goes on. 

It is difficult to work out the exact wind direction at altitude without floating a sounding balloon through that layer.

What I do is look at upper atmosphere weather charts to give me this information.
Title: Re: Cloud movement and direction
Post by: Lost Soul on August 06, 2012, 10:39:52 AM
Basically wind is affected by friction of the earth’s surface and rotation (Coriolis forces).  Which ensures the surface winds are different to upper winds.  Aviator’s use a simple rule of thumb to determine winds at 2000 feet-ish.  As height increase so do the numbers for speed and direction.  Add 30 degrees to the surface direction to get the 2000 foot direction.  So if surface direction is 210 deg then at 2000 feet it will be 240 deg. 

Now this is a rule of thumb and wind direction is notoriously fickle and difficult to predict.  However, this rule is reasonably accurate for the heights at which all that fluffy and broken stuff exists - 1000 to 5000 feet.  Which realistically is the stuff you are going to be able to observe and follow its motion.

The Met Office ( http://www.metoffice.gov.uk/aviation/ga-briefing-services ) produces spot wind height charts for aviators.  Form F214.  And if you want to know what cloud type and heights to expect then try looking at F215 Low Level Weather Chart which provides weather and cloud up to 10,000 feet.  It is written in an internationally standardised “code” but decode material is readily available from the Met Office Web site.

Going back to the F214.  For to-day the predicted winds for 5230n 0230W are

1000 feet    280 deg      10 kts
2000      280      10
5000      270      15
10000      250      15
18000      260      10
24000      300      15

As you can see a reasonably consistent westerly.

So in answer to you question Does anyone know of a technique that can be used by walkers to establish, with reasonable accuracy, the direction in which clouds are moving?  Suggest you try using the aviators rule of thumb.  Add 30 deg to the surface wind and see how you get on.

Hope this helps.
Title: Re: Cloud movement and direction
Post by: Lyle Brotherton on August 06, 2012, 02:03:26 PM
Great to see you back from your travels Adi and good your fit and well :)

Really interesting post Adi and I have not encountered this system before Leon.

Weather systems fascinate me and I know that you two are much better informed then I am ;)

Two books that I refer to and think are excellent are:

The Cloudspotter’s Guide, by Gavin Pretor-Pinney, (Pub by Sceptre, 2007)
One of those novel books that has really taken off and I can see why. It very entertainingly explains how and why clouds form, and demystifies a lot of the meteriorlogical science and keep the Latin names to the bare minimum. But it goes further than this and explores man’s relationship with clouds and how we have engaged with them in art and literature. The fact that I liked was that the Greek playwright, Aristophanes, described them as the ever-present, subtle backdrop to the whole of human existence.

Pocket Weather Forecaster by Simon Keeling (Pub by Simon Keeling, 2009)
This guy is as fanatical about weather systems as I am navigation and I have enjoyed some great conversations with him. He runs 2/3 day weather courses, mainly for aircraft pilots and maritime navigators, and when I find time I intend to go on one.

I think that this subject is so closely aligned with navigation it should have its own topic setting, anyone second my proposal?
Title: Re: Cloud movement and direction
Post by: Lost Soul on August 06, 2012, 03:54:24 PM
Hi Lyle

Yes I second your proposal and agree with your reasons for it.  Understanding weather, what you've got what you are likely to get influences (or should) route planning and micronav.  As your own material informs us, headwinds slow you down so pacing and timing is going to be affected.

Hill Walking and Winter Skills both published by Mountain Leader Training UK have chapters on weather aimed specifically at walkers.

Also you might like to try this web site http://www.raintoday.co.uk/  Radar pictures of where the wet stuff, whom it is currently laying waste to, who is likely to get it next and when.  And try this one for your Smartphone / PDA   pda.meteox.com
Title: Re: Cloud movement and direction
Post by: Hugh Westacott on August 06, 2012, 04:40:40 PM
As the OP (original poster), i support your suggestion of a topic dedicated to the weather.

Thanks for your responses. I understand the basics of meteorology. However, the purpose of my query was practical rather than theoretical. When leading walks on a showery day, I'm often asked by my lovely ladies whether they should keep wearing their rain gear once a shower has passed. I've often wondered whether there is a technique that would allow me to quickly establish the direction of cloud movement and relate this to my general direction of travel so that I could  make an educated guess as to whether we were going to be caught by the next black ground.

Any ideas?

Hugh
Title: Re: Cloud movement and direction
Post by: adi on August 06, 2012, 07:45:19 PM
I find doing my own forecasts are far better than that offered by the MetO. because i can forecast for my desired area and take the accuracy up. Weather companies around the world only need to give a accuracy of around 80% because they forecast to many people over a large area.

The MetO are very protective over their data, they earn millions of pounds from it so can't blame them although they is they do publish some info if you spend the time looking.

They limit the amount of model data they publish to only 2 model run, first at 1200 hours and the second at 0000 hours and they only publish data out to 120 hours, the most famous is the FAX chart.

There are loads of weather models produced every day by different countries. Some are GFS (Global forcast system, from the US); NOGAPS  (U. S. Navy's Operational Global Atmospheric Prediction System); ECMWF (support to European meteorological organizations) that is just 3 of many more. All offer data to some extent or other.

GFS offers the most data which goes out to 384 hours although at this distance the data is known as FI (fantasy island), It is relatively reliable out to 180 hour. GFS publish 4 runs a day and they publish all of their data a large amount of it is free the rest is by subscription from any one of the many providers.

Each model has its strengths and weaknesses, GFS often over cooks Rain fall amounts, wind speeds and for the UK convective potential, saying that though it is one of the only models that makes convective data available. ECMWF have the most accurate plotting for low pressure systems. MetO has many strengths but sadly most are not available to the public, one being the highest resolution data for mush of the world. Of course they make FAX charts available which are very useful.

Access to some free basic charts http://www.netweather.tv/index.cgi?action=nwdc;sess=

One of the most annoying things about the MetO is that they are moving to computerised data collection which is fine for station observations but they are slowly closing all the upper air sounding stations. I use this data for convective weather forecasting. The Charts are known as Skew T

Skew T can be seen here http://meteocentre.com/upper/uk.html?lang=en click on the chart.

For me upper air observations give me information that is vital for convective weather

Right I have posted links to enough charts to confuse you for a life time so I will shut up now.

Title: Re: Cloud movement and direction
Post by: adi on August 06, 2012, 07:55:20 PM
Subscribe to one of the many rain radar apps on your mobile and look at that or keep an eye up wind, may be?
Title: Re: Cloud movement and direction
Post by: Lost Soul on August 06, 2012, 08:03:12 PM
I don't think you are going to get much more accurate than I said in my origional reply.

However,  as a complete technique try this.

1.  Roughly face into the wind.  Close your eyes, and slowly turn your whole body this way and that until you feel the wind equally in both cheeks.  Keep your position open your eyes and take a compass bearing facing forward.  This is the direction the wind is coming from. e.g 210 deg

2.  Add 30 degrees to it.  This is the direction the clouds are coming from. e.g 240 deg

3.  If less than 180 deg then add 180 or, if more than 180 subtract 180.  This gives you the direction of travel of the clouds. eg. 240 - 180 = 060.

4.  Draw a prominent arrow line on your map pointing 060.

5.  From the map, by knowing your position and current direction of travel you will have a pictorial representation of cloud travel in relation to your direction of travel.

Hope this helps
Title: Re: Cloud movement and direction
Post by: adi on August 06, 2012, 08:22:41 PM
Basically wind is affected by friction of the earth’s surface and rotation (Coriolis forces).  Which ensures the surface winds are different to upper winds.  Aviator’s use a simple rule of thumb to determine winds at 2000 feet-ish.  As height increase so do the numbers for speed and direction.  Add 30 degrees to the surface direction to get the 2000 foot direction.  So if surface direction is 210 deg then at 2000 feet it will be 240 deg. 

Now this is a rule of thumb and wind direction is notoriously fickle and difficult to predict.  However, this rule is reasonably accurate for the heights at which all that fluffy and broken stuff exists - 1000 to 5000 feet.  Which realistically is the stuff you are going to be able to observe and follow its motion.

The Met Office ( http://www.metoffice.gov.uk/aviation/ga-briefing-services ) produces spot wind height charts for aviators.  Form F214.  And if you want to know what cloud type and heights to expect then try looking at F215 Low Level Weather Chart which provides weather and cloud up to 10,000 feet.  It is written in an internationally standardised “code” but decode material is readily available from the Met Office Web site.

Going back to the F214.  For to-day the predicted winds for 5230n 0230W are

1000 feet    280 deg      10 kts
2000      280      10
5000      270      15
10000      250      15
18000      260      10
24000      300      15

As you can see a reasonably consistent westerly.

So in answer to you question Does anyone know of a technique that can be used by walkers to establish, with reasonable accuracy, the direction in which clouds are moving?  Suggest you try using the aviators rule of thumb.  Add 30 deg to the surface wind and see how you get on.

Hope this helps.

Interesting Post Lost Soul. I have not seen this before. Is it something from aviation weather?

I need to question it because I have seen many Hodographs showing vertical shear greater than 30°.

On this sounding from today the wind can be seen to come form 180° to that at ground level.

 
Title: Re: Cloud movement and direction
Post by: Lost Soul on August 06, 2012, 09:16:24 PM
Yes, what I wrote there is bog standard piloting technique - been taught that way for the past 100 years.  It works believe me, not withstanding local wind effects which you wont really get in open countryside.  And yes that was the official UK Met Office aviation weather forcast for this morning for altitudes from 1000 feet to 24000 feet.  Basically its what all pilots of light aircaft and commuter aircaft use.  Irrespective of whether they get it direct from the Met Office or from a service reseller.  I have never had any real problem with them.  As long as one accepts them for what they are, forecasts, best guesses.  The only true informations about weather are of course actuals and aftercasts.  The former tells you, yes the wind is blowing from this direction and the later that the wind was blowing in that direction.  The former you use to make real time decisions about what your next action is going to be and the latter for accident investigation and coroners inquests!!
Title: Re: Cloud movement and direction
Post by: adi on August 06, 2012, 09:59:13 PM
Ok please bare with me I am dyslexic and need to sort things out in my head before I understand something.

From what I read of your post you are saying that the surface wind blows at 0° degrees then it can only blow +/-30° above the surface at 2000'.

So are you saying the wind can only change direction by 30° in a 2000' layer of space?  You have lost me completely. 

Not many aircraft fly at 2000'.

If you ever get the chance to storm chase a supercell storm you can see vertical shear of greater than 30° in action.

I have just found this video that clearly shows the low level cloud travelling in the opposite direction from the upper level cloud.

http://www.youtube.com/watch?v=bIY9dfZNhZE
Title: Re: Cloud movement and direction
Post by: Skills4Survival on August 06, 2012, 10:54:17 PM
funny, never saw clouds move so fast  :)  Help me here pls, why do I want to know the direction clouds are moving (on micro level), is that crucial knowledge to predict local weather or has it other reasons? I do not have a lot of experience with mountain wheather (a few weeks in cairgorms did make me consider some things now and then though).  I just use the wet finger a few times before I pitch camp.
Title: Re: Cloud movement and direction
Post by: adi on August 07, 2012, 02:12:37 PM
The cloud is moving so fast because it is a time lapse film.

Know in what direction the wind is blowing can help speed you on your trip, You don't need to look at your map so often.  Hugh asked so he can try to tell his ladies if they can take their waterproofs off, Although I am not sure there is an answer to that other than having a good forecast available before you head out.

In a survival environment knowing the prevailing wind direction can be very useful. It might give you a clue to the direction out of there.

I know of a story where a Canadian Backs woodsman was blinded by an accident whilst out on the trap line and he was able to walk back to a large town some 80 miles away by using the wind and the smells that were carried by the wind. He was up on a plateau and knew the valley he needed to take him down to the lowlands was lined with Aspen and was the only one around. So once he smelled the Aspen he followed his nose, after some time the ground started to drop away, so he through snow balls down the slop, If he heard them land he moved in that direction until he was in the valley. he then headed down the valley for 6 days, sometimes up to his chest in snow to come out at the bottom and then again followed his nose and the smells that large towns give off.

I think his trip took him 9 days in total to get himself to a place of safety. Ok he had bags of local knowledge, he knew exactly were he was when the accident happened and he was lucky he was able to find the smell of the Aspen on his first day. These old pioneer stories were so remarkable at the time that they passed into folk law and were committed to print.
Title: Re: Cloud movement and direction
Post by: Skills4Survival on August 07, 2012, 06:34:02 PM
I know that, hence the smiley :-), my kind of humor.
Yes, the prevailing wind I am clear on. Also, out of which direction the wind comes...I can see with my compass, I just do not understand the whole difficulty of determining the cloud thing

1. step one, feel wind
2. step two read compass
3. do not forget..and use it if needed.

So wind, understand, cloud direction...that part I do not see yet, why that would really add value to what we would want to achieve.
Title: Re: Cloud movement and direction
Post by: Lost Soul on August 08, 2012, 07:28:51 PM
Adi,

To respond to your post.

From what I read of your post you are saying that the surface wind blows at 0° degrees then it can only blow +/-30° above the surface at 2000'.

More or less correct.   To be specific +30° in the Northern Hemisphere and -30° in the Southern Hemisphere

So are you saying the wind can only change direction by 30° in a 2000' layer of space?  You have lost me completely.

Yes , let me help your understanding.  A fundamental and undeniable fact and proven principal of atmospheric physics is that the atmosphere consists of high and low pressure systems constantly on the move.  Each system covers many hundreds of square miles of the Earth's surface.  These pressure systems have pressure gradients across them.  These gradients are represented by isobars on a weather chart in exactly the same way that we represent gradients (hills and valleys) across the landscape by contour lines.  At heights at above 2000 feet and above the air moves around the pressure systems parallel to the isobars. 

This movement of the air is of course the wind.  At heights above 2000 feet other factors may or may not come into play and disturb the direction of that flow,  Below 2000 feet friction generated by the Earth's surface causes this air movement to slowdown and in so doing change direction by 30°.  So if you are in the northern hemisphere and the wind is blowing 0° at 2000 feet on the ground level it will be 330°.  i.e backed by 30°.

This fundamental principle is taught on day one on any metrological course.  Certainly to forecasters, met observers and anyone else who has an interest in the upper winds.  It is one of the cornerstones of meteorology.  If you want a good brief explanation of it then I recommend you to read the Air Pilots Weather Guide by Ingrid Holford.  Chapter 3 deals with pressure winds.

Not many aircraft fly at 2000'.

Yes they do.  Most light aircraft to fly at that height.  When pilots are being taught to fly this is the altitude of choice for various reasons.  Not least of which is that we tend to suffer low cloud bases in this country and the vast majority of light aircraft must maintain visual contact with the ground below.  Because they just do not have the instrumentation required for them to fly in cloud and neither do the pilots have the appropriate training or qualification to do so. 

So as you can well imagine there are many hundreds of flights per day at 2000 foot level or there abouts.  Also many helicopters fly at these levels or lower.  The vast North Sea offshore helicopter support operations running out of Aberdeen and Sumburgh fly at the 2000 to 3000 foot level.  And on a good day there are more flights across the North Sea Oil fields by helicopters then there are out of Heathrow on a peak summer weekend.

If you ever get the chance to storm chase a supercell storm you can see vertical shear of greater than 30° in action.

Yes I am fully aware of the vertical shear that exists in a super cells or even lesser thunderstorms.  The vertical winds traveling both up and down to devastating effect.  On the down motion it can burst out of the bottom of the storm cloud hit the ground with considerable energy and disperse in all directions of the compass.  Its effect being felt up to 20 miles away.  This is what is known as a micro burst and is of course a localised atmospheric wind effect.

I have just found this video that clearly shows the low level cloud travelling in the opposite direction from the upper level cloud.

Yes the video demonstrate horizontal wind shear.  Probably a very localised phenomena brought about by features of the landscape.  If you know where to look on the Internet you can find all sorts of videos showing weird and wonderful weather effects.  But they do not disprove the fundamental principles of air mass movement around an atmospheric pressure system.  Surface winds are affected by all sorts of low-level effects such as hills, valleys, buildings and surface heating. 

Which is something you are clearly very conversant with and is also discussed in the book reference given above.  As I said in my very first post wind direction is notoriously fickle and difficult to predict; particularly at ground level for the reasons given above.  However, on open ground such as the Essex Marshes, Exmoor the tops of the South Downs etc those effects don’t really exist other than perhaps on-shore breezes on a very hot day, so the wind backing by 30° at the surface will hold good.  But there again for an on shore breeze to form to any great effect general surface winds have to be light.  Which indicates the presnce of a high pressure system, clear skies and no likely hood of any weather.

And yes I appreciate that for your local area you like to predict convective weather (ultimately thunderstorms I assume ) from tepigrams.   Building up a data base, if only a mental one, of what sort of patterns in a tepigram will give a probability of a thunderstorm in your local area is a neat skill indeed.  However, what we have done I believe is both answered Hugh Westacott’s question from differing view points.

As he says he just wants to be able to tell his ladies if they need to keep their water proofs on or not.  And I very much doubt if they will be venturing out when the weather is serious and thundery or in remote mountain areas.  Interestingly MLTs Hill Walking Manual which discusses weather doesn’t go into any of this stuff about upper winds that you and I have been going on about. Unfortunately, we have done what so often happens in these forums.  We have hijacked a simple question and set it off spinning in a different irrelevant direction.  All Hugh required was a simple, practical, instantly usable answer to a simple question.

As Skills4Survival says in his posts: Yes, the prevailing wind I am clear on. Also, out of which direction the wind comes...I can see with my compass, I just do not understand the whole difficulty of determining the cloud thing

1. step one, feel wind
2. step two read compass
3. do not forget..and use it if needed.

So wind, understand, cloud direction...that part I do not see yet, why that would really add value to what we would want to achieve.
 
I just use the wet finger a few times before I pitch camp.


That neatly brings it all back on track and we should leave it there.
Title: Re: Cloud movement and direction
Post by: Skills4Survival on August 08, 2012, 10:02:23 PM
Just to make sure, it was not meant in a bad way. I understand a little bit of what has been said, just because I studied geography a long time ago. I honestly did not see the fit into practical navigation or survival for that matter (but open for suggestions!)

It is however insightfull and I thank you for it. I do believe that knowing a little bit about wind, weather systems, high/low pressure, pressure changes, etc. can be helpful in specific situations.

greetz,

Ivo

Title: Re: Cloud movement and direction
Post by: Rescuerkw on August 08, 2012, 11:43:27 PM
Well guys you've completely lost me with all that technical stuff. In the lowland areas of East Anglia where I reside, the prevailing wind in a useful indicator of direction, but of course we don't have those large protrusions in our landscape that you guys call hills and mountains. In our 'big sky' part of the UK an approaching weather change is usually quite easy to see and because it's not subject the massive terrain undulations that one will find in the Peaks or the Lake district, it tends to be a lot more predictable and more often than not does what it looks like it going to do. So, when I'm out with the ladies and I see a big black cloud approaching, I usually suggest that we all put our waterproofs on. As you can tell, an incredibly scientific approach - but in fact as you will know if you've read some of my other posts I love to keep all this stuff as simple as possible (maybe a reflection of my character?)
Title: Re: Cloud movement and direction
Post by: Skills4Survival on August 09, 2012, 09:07:15 AM
I do the same and sometimes I do it in the morning  :D . If possible I know the general (local) wheather forecast, more related to day planning if needed and just be a bit more comfortable on possible risks, e.g. snowfall and prepare smartly.
Title: Re: Cloud movement and direction
Post by: Lyle Brotherton on August 09, 2012, 11:48:10 AM
I have learned more from this thread than all the books I mentioned earlier, really interesting and some fantastic info.

You guys are experts - Ron, I am currently at your level of understanding ;)
Title: Re: Cloud movement and direction
Post by: adi on August 09, 2012, 09:38:13 PM
I will point out you are correct about the surface wind being at 30° to the Isobars of a pressure system this is known as the angle of indraft.

I have just emptied my shelf of all my meteorological books and I am now sat in the middle of them.
Title: Re: Cloud movement and direction
Post by: adi on August 10, 2012, 12:02:43 AM
Right I have got to the bottom of this. Quoting the book Weather and Forecasting by Storm Dunlop & Francis Wilson, Octopus Publishing Group, 1982 'The angle which the winds make to the Isobars depends on the surface friction and will be at least (about 10° - 20° over sea and greater (about 25° - 35°) over land. This frictional effect lessons with height and so gives rise to a shift in the wind direction. At 500 - 1000 meters (1640 - 3280 ft) the wind is flowing freely along the isobar.' Cloud is usually above this dirty air so are not effected by friction so normally show the real wind direction although it is important to remember wind at different heights can go in different directions.   

One small paragraph in one book out of 12!   

LOL I wish i did only predict convective weather for my location, I produce convective forecasts for the States, much of Europe and the whole of the UK depending where people are at the time. Today I gave two general 3 day forecasts, one was for Winston-Salem, North Carolina and Washington, Virginia and a convective forecast for Whitesburg, Kentucky, this one is for a local radio station that I have a contract to give out of hours weather updates when they are under a watch.
Title: Re: Cloud movement and direction
Post by: Callum on August 10, 2012, 08:23:37 AM
This posting has taken a lot of re-reading for me to get to grips with, and I think that I have now.

Lost Soul and Adi, yes it has spun off in different directions, but I personally am pleased that it has, as it has made me study the subject in greater detail and actually fired up my interest, so again, thanks guys :)
Title: Re: Cloud movement and direction
Post by: Pete McK on August 10, 2012, 05:41:16 PM
Like Cal, I have really enjoyed this thread, which book would you guys recommend as a beginners introduction?
Title: Re: Cloud movement and direction
Post by: Skills4Survival on August 10, 2012, 06:00:52 PM
you could look at chapter 8 of "hillwalking" of steve long. I also like "how to identify the weather" by storm dunlop 2002, harper collins
Title: Re: Cloud movement and direction
Post by: adi on August 10, 2012, 06:00:59 PM
wow Pete that is a hard one, it depends how technical you want.

This might be a good place to start it covers the basics
http://www.amazon.co.uk/Weather-Hillwalkers-Climbers-Leisure-Interests/dp/0750910801 (http://www.amazon.co.uk/Weather-Hillwalkers-Climbers-Leisure-Interests/dp/0750910801)

Title: Re: Cloud movement and direction
Post by: Lost Soul on August 10, 2012, 06:50:55 PM
From a practical point of view to get you started with very little technicalities involved.  I suggest you try Chapter 8 of Hill Walking by Steve Long.  That will give you a basic introduction.  Follow that up with Chapter 3 of Winter Skills by Cunningham and Fyfe.  That gives a top for winter conditions.  Both published by Mountain Leader Training.

I am not sure if this one is still published but it’s very useful.  Instant Weather Forecasting by Alan Watts published by Adlard Coles.  Basically a pictorial guide to sky conditions and what they mean and what you can expect in terms of approaching weather. Actually that would be useful to Hugh re his original posts – when do I advise my ladies that they can remove thier waterproofs / they need to keep them on.

On a similar vein try the Cloud Book by Richard Hamblyn, Published by the Met Office.

And Adi, re your post of this morning I am pleased we concur on all points raised.
Title: Re: Cloud movement and direction
Post by: adi on August 10, 2012, 07:05:22 PM
Yeah Instant Weather Forecasting by Alan Watts is a good book to learn now-casting by looking at the sky.

And one of the best books on synoptic weather is 'Outlook Weather maps and Elementary Forecasting' By G.W. White, first published in 1967. unfortunately it is like rocking horse poo to get now. And some of the stuff covered has been superseded by better understanding and modern technology but it is one of the best books for describing air masses and frontal systems.
Title: Re: Cloud movement and direction
Post by: Hugh Westacott on August 19, 2012, 06:51:49 AM
Thanks chaps for all your responses.

The reason for posting my question bordered on the frivolous but I feel vindicated because it resulted in a fascinating discussion from which I, and I suspect other members of this forum, have learnt a lot.

Hugh
Title: Re: Cloud movement and direction
Post by: adi on August 19, 2012, 05:51:57 PM
Not a problem Hugh there is no such thing as stupid question only stupid answers!

I leaned something from lost Soul. surface wind measurements for the meteorologist are measured at 10 meter above the ground and these blow at 30° to the isobars at this height thanks to friction. What I learnt was that from 500 to 1000 meters the wind is no longer effected by friction. Not that important for server weather forecasting but hugely important for aviation. 
Title: Re: Cloud movement and direction
Post by: MoonMan on September 15, 2013, 08:06:07 AM
I take note of cloud direction, versus ground wind, if either be available. Today's upper level wind usually is tomorrow's ground wind. Comes in handy for how to pitch a shelter, overnight. Buy-Ballot's Law is handy to heed: Northern Hemisphere version, with wind at back, Low Pressure Cell is on Left & ahead; Southern Hemisphere version: Low Pressure Cell is on Right & ahead. The stronger the wind, the closer the cell.
Title: Re: Cloud movement and direction
Post by: Callum on September 15, 2013, 09:16:12 AM
We used to have a small booklet, A5 size, that had colour glossy photographs, each page,  of different cloud formations and instructions on each of these pages about which way to face, regarding wind direction versus cloud movement. It was a really handy booklet and very reliable in its forecasts, however its owner was not so reliable and not only lost it but can't even remember what it was called ::) Can anyone remember it possible title?
Title: Re: Cloud movement and direction
Post by: Hugh Westacott on September 15, 2013, 10:06:33 AM
Callum

I have two books that cover the subject:

Mountain Weather by David Pedgley, Cicerone, 2nd ed 1997. (There may be a later edition)
Mountain Weather for Climbers by David J. Unwin, Cordee, 1978. (Cordee has cesed publishing and is now a book distributor)

Hugh
Title: Re: Cloud movement and direction
Post by: Pete McK on September 15, 2013, 10:16:08 AM
Cal, I suspect you might be referring to Simon Keelings book - The Pocket Weather Forecaster I have checked it is still available and it is a great read :)

Hugh, I don't know these titles, which would you recommend please?
Title: Re: Cloud movement and direction
Post by: Hugh Westacott on September 15, 2013, 12:41:32 PM
Pete

Unwin's book was published in 1978, has not been updated and is out of print

The 2nd ed of Pedgley's book was published in 2009. The author is an OBE (Order of the British Empire) and has worked s a weather observer, forecaster, and instructor in the Meteorological Office so he should know his onions.

I have only a passing interest in the weather but, judging from the publication date and the numerous photographs of cloud formations, I'm inclined to the opinion that Pedgley has written a more useful book. Howevr, it does not match the description of the book that Callum had in mind.

Hugh
Title: Re: Cloud movement and direction
Post by: Callum on September 16, 2013, 05:33:31 PM
Spot on Pete, many thx:) I was given my dog eared copy by a colleague who was retiring and had just started to get into the habit of using for forecasting with it, when I left it on some fell – I think I need lanyards for everything nowadays
Title: Re: Cloud movement and direction
Post by: MoonMan on September 17, 2013, 08:12:42 AM
Collins GEM WEATHER photoguide covers just about everything that is seen in the Sky by way of Clouds & other phenomena; was UKP 3.99, fits into the pocket