Author Topic: Cloud movement and direction  (Read 18771 times)

Hugh Westacott

  • Sr. Member
  • ****
  • Posts: 306
    • View Profile
    • Walk with Westacott
Cloud movement and direction
« 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

adi

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 548
    • View Profile
Re: Cloud movement and direction
« Reply #1 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.
"We do not belong to those who only get their thought from books, or at the prompting of books - it is our custom to think in the open air, walking, leaping, climbing or dancing, of lonesome mountains by preference, or close to the sea, where even the paths become thoughtful." Friedrich Nietzsche

Lost Soul

  • Sr. Member
  • ****
  • Posts: 265
    • View Profile
Re: Cloud movement and direction
« Reply #2 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.
« Last Edit: August 06, 2012, 03:33:36 PM by Lost Soul »

Lyle Brotherton

  • Administrator
  • Hero Member
  • *****
  • Posts: 939
  • Competent and safe navigation sets you free.
    • View Profile
Re: Cloud movement and direction
« Reply #3 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?
“Opinion is the medium between knowledge and ignorance” - Plato

Lost Soul

  • Sr. Member
  • ****
  • Posts: 265
    • View Profile
Re: Cloud movement and direction
« Reply #4 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

Hugh Westacott

  • Sr. Member
  • ****
  • Posts: 306
    • View Profile
    • Walk with Westacott
Re: Cloud movement and direction
« Reply #5 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

adi

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 548
    • View Profile
Re: Cloud movement and direction
« Reply #6 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.

"We do not belong to those who only get their thought from books, or at the prompting of books - it is our custom to think in the open air, walking, leaping, climbing or dancing, of lonesome mountains by preference, or close to the sea, where even the paths become thoughtful." Friedrich Nietzsche

adi

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 548
    • View Profile
Re: Cloud movement and direction
« Reply #7 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?
"We do not belong to those who only get their thought from books, or at the prompting of books - it is our custom to think in the open air, walking, leaping, climbing or dancing, of lonesome mountains by preference, or close to the sea, where even the paths become thoughtful." Friedrich Nietzsche

Lost Soul

  • Sr. Member
  • ****
  • Posts: 265
    • View Profile
Re: Cloud movement and direction
« Reply #8 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

adi

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 548
    • View Profile
Re: Cloud movement and direction
« Reply #9 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.

 
"We do not belong to those who only get their thought from books, or at the prompting of books - it is our custom to think in the open air, walking, leaping, climbing or dancing, of lonesome mountains by preference, or close to the sea, where even the paths become thoughtful." Friedrich Nietzsche

Lost Soul

  • Sr. Member
  • ****
  • Posts: 265
    • View Profile
Re: Cloud movement and direction
« Reply #10 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!!

adi

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 548
    • View Profile
Re: Cloud movement and direction
« Reply #11 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.

<a href="http://www.youtube.com/watch?v=bIY9dfZNhZE" target="_blank">http://www.youtube.com/watch?v=bIY9dfZNhZE</a>
"We do not belong to those who only get their thought from books, or at the prompting of books - it is our custom to think in the open air, walking, leaping, climbing or dancing, of lonesome mountains by preference, or close to the sea, where even the paths become thoughtful." Friedrich Nietzsche

Skills4Survival

  • Full Member
  • ***
  • Posts: 235
  • Know the concepts !
    • View Profile
Re: Cloud movement and direction
« Reply #12 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.
Ivo

adi

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 548
    • View Profile
Re: Cloud movement and direction
« Reply #13 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.
"We do not belong to those who only get their thought from books, or at the prompting of books - it is our custom to think in the open air, walking, leaping, climbing or dancing, of lonesome mountains by preference, or close to the sea, where even the paths become thoughtful." Friedrich Nietzsche

Skills4Survival

  • Full Member
  • ***
  • Posts: 235
  • Know the concepts !
    • View Profile
Re: Cloud movement and direction
« Reply #14 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.
Ivo