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Hello everyone. There's a number of things I don't understand about the weather. I'd love just to go into the model thread and know what everyone is talking about. Despite me being interested in the weather for about 3 years, I am still a complete newbie to it.

First of all, the chart below. What does it show? I know 528 DAM is needed for snow, so in the far right hand corner of this chart where 528 is showing would that mean any precip that falls in that area will be of snow?

Also what impact does thickness have on the weather?

528dam.png

This chart underneathe shows pressure and upper temperatures, but what do the colours mean, and at what height are the upper temperatures measured at?

h850t850eu1.png

What does the chart underneathe show?

0degisotherm1.png

What does CAPE mean, what does it do, and what numbers do I need to look for to predict a thunderstorm?

ukcapeli1.png

And I now have a few questions. :shok:

1) How do you predict a change in wind direction?

2) What is a wet bulb temperature?

3) What is a dry bulb temperature?

4) I know what the dew point does and I know that it needs to be at or below 0c for snowfall, but what actually is it?

5) What conditions do I need to look for, for frost around this time of year, other than temperatures below 0c?

6) What is a trough?

7) How do you forecast and see on a chart, a mild sector?

I know it's alot but I really want to get into this kind of thing, to who ever answers, thank you so very much!!

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Cape is the energey and unstableness in the atmosphere. The higher the cape the more unstable it is and the more energey is in the air. In a good US cell the cape is around 3500 although in the uk we get around 1000 as a maximum :shok:. So to sum it all up the more cape you have the morelikey a cell might pop up and be thundery and the more unstable the atmosphere is :cray: I am lead to belive cape is what makes in some cases towering cloumbis ( sorry been a while since i spelt it), please correct me if i am wrong :)

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Cape is the energey and unstableness in the atmosphere. The higher the cape the more unstable it is and the more energey is in the air. In a good US cell the cape is around 3500 although in the uk we get around 1000 as a maximum :(. So to sum it all up the more cape you have the morelikey a cell might pop up and be thundery and the more unstable the atmosphere is :) I am lead to belive cape is what makes in some cases towering cloumbis ( sorry been a while since i spelt it), please correct me if i am wrong :)

Thanks alot mate, really helped me understand CAPE. :D

cumulonimbus? :acute:

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What vortex forgot to mention was LI (lifted Index) which measures how boyant the airmass is the lower the number the more unstable the air is.

in this chart the air is very boyant and the cape is at 0 J/kg meaning that basically theres no chance of a storm, over belgium/netherlands they have a chance of seeing a storm as there Cape is up around 700-900 J/kg and there lifted index is -2/3 C but these conditions don't mean that you will definatley get a storm.

ukcapeli1.png

we see the cape (colours) and the LI (numbers) basically the darker more vivid the colours the more energy is in the atmophere and the lower numbers (-6/7) how unstable it is!

Just to get your head around it the strongest ever tornado was recorded on may 3rd 1999 in Moore, Oklahoma the storm that produced that tornado was feeding on nearlly 6000 J/kgs of cape which is phenomenal and -8 LI C, as we all know that tornado produced 300+mph winds.

like vortex said the UK gets no where near that and very rarely gets up too 1000 J/kg

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Thank you very much Mesoscale. So the lower that number the more unstable the atmosphere? Seems pretty straight forward. Why can't all charts be that straightforward. :winky:

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Not got a great deal of time, but will try to quickly answer some of your questions:

First of all, the chart below. What does it show? I know 528 DAM is needed for snow, so in the far right hand corner of this chart where 528 is showing would that mean any precip that falls in that area will be of snow?

Also what impact does thickness have on the weather?

Thickness in this case is a measurement of the height difference between 500mb and 1000mb (these are measures of air pressure), the further between the two heights, the warmer the airmass is. 528DAM (DAM stands for decameters - 1 dam = 10 metres) is a commonly used rain/snow line, so as a general rule for there to be a risk of snow the thickness needs to be below 528.

This chart underneathe shows pressure and upper temperatures, but what do the colours mean, and at what height are the upper temperatures measured at?

That chart is showing the temperature at 850mb (or hpa), which is approx 1.5km above sea level. The colours show the temperature in celcius. If you're looking for snow risk, you need the temperature to be below -5c as a general rule.

What does the chart underneathe show?

That's the freezing level (0c isotherm), so the figures on there are metres, and shows the level that the temperature is at 0c. Again it's a useful chart for snow prediction - you'll be looking for the 0c isotherm to be at 200-300 metres or below for snow to fall at sea level in most instances. It's also a handy chart for predicting whether showers/storms will produce hail.

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hi

I'm not very well so answering those questions is beyond me at the moment but Paul has done a good job. I gather you feel the guides are not showing the things you want but try this link

http://forum.netweather.tv/forum/5-the-netweather-guides/page__prune_day__100__sort_by__Z-A__sort_key__last_post__topicfilter__all__st__25

dewpoints, weather systems and air masses are described there, they seemed to work a few mins ago.

The main thing, please don't feel I'm talking down to you, is walk before you try to run. Meteorology is a very complex subject, its best to start simple and slowly build up. I know the section on skew-t diagrams has some problems but that will, if you spend time on it, help you understand about the atmosphere. Please do read the Guides, several of us have posted in there and they are worth reading.

If, when you have done all that you have any questions, then like you have above, ask questions, someone on Net Wx will try to answer you.

enjoy the weather.

John

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Not got a great deal of time, but will try to quickly answer some of your questions:

Thickness in this case is a measurement of the height difference between 500mb and 1000mb (these are measures of air pressure), the further between the two heights, the warmer the airmass is. 528DAM (DAM stands for decameters - 1 dam = 10 metres) is a commonly used rain/snow line, so as a general rule for there to be a risk of snow the thickness needs to be below 528.

That chart is showing the temperature at 850mb (or hpa), which is approx 1.5km above sea level. The colours show the temperature in celcius. If you're looking for snow risk, you need the temperature to be below -5c as a general rule.

That's the freezing level (0c isotherm), so the figures on there are metres, and shows the level that the temperature is at 0c. Again it's a useful chart for snow prediction - you'll be looking for the 0c isotherm to be at 200-300 metres or below for snow to fall at sea level in most instances. It's also a handy chart for predicting whether showers/storms will produce hail.

hi

I'm not very well so answering those questions is beyond me at the moment but Paul has done a good job. I gather you feel the guides are not showing the things you want but try this link

http://forum.netweat...er__all__st__25

dewpoints, weather systems and air masses are described there, they seemed to work a few mins ago.

The main thing, please don't feel I'm talking down to you, is walk before you try to run. Meteorology is a very complex subject, its best to start simple and slowly build up. I know the section on skew-t diagrams has some problems but that will, if you spend time on it, help you understand about the atmosphere. Please do read the Guides, several of us have posted in there and they are worth reading.

If, when you have done all that you have any questions, then like you have above, ask questions, someone on Net Wx will try to answer you.

enjoy the weather.

John

Paul and John, words cannot describe how grateful I am at the moment, thank you so very bloody much! Maybe now I can go into the model output discussion and understand what they are actually saying!

Thanks John, i'll read your Skew-T guides right now. Thanks again guys I appreciate this so much!

:good:

Edit: Hope you get well soon John!

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Not got a great deal of time, but will try to quickly answer some of your questions:

Thickness in this case is a measurement of the height difference between 500mb and 1000mb (these are measures of air pressure), the further between the two heights, the warmer the airmass is. 528DAM (DAM stands for decameters - 1 dam = 10 metres) is a commonly used rain/snow line, so as a general rule for there to be a risk of snow the thickness needs to be below 528.

That chart is showing the temperature at 850mb (or hpa), which is approx 1.5km above sea level. The colours show the temperature in celcius. If you're looking for snow risk, you need the temperature to be below -5c as a general rule.

That's the freezing level (0c isotherm), so the figures on there are metres, and shows the level that the temperature is at 0c. Again it's a useful chart for snow prediction - you'll be looking for the 0c isotherm to be at 200-300 metres or below for snow to fall at sea level in most instances. It's also a handy chart for predicting whether showers/storms will produce hail.

One last question if you don't mind Paul. I'm actually a big fan of hail, and living so close to the Irish sea I get more than pretty much everywhere in Winter. How would I predict hail?

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hello backtrack

thanks for the good wishes I'll survive.

re these

And I now have a few questions. :(

1) How do you predict a change in wind direction?

2) What is a wet bulb temperature?

3) What is a dry bulb temperature?

4) I know what the dew point does and I know that it needs to be at or below 0c for snowfall, but what actually is it?

5) What conditions do I need to look for, for frost around this time of year, other than temperatures below 0c?

6) What is a trough?

7) How do you forecast and see on a chart, a mild sector?

I will get round to trying to explain them, dewpoint in particular is very inmportant, give me time and I'll drop a pdf link into this thread.

John

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hello backtrack

thanks for the good wishes I'll survive.

re these

And I now have a few questions. :(

1) How do you predict a change in wind direction?

2) What is a wet bulb temperature?

3) What is a dry bulb temperature?

4) I know what the dew point does and I know that it needs to be at or below 0c for snowfall, but what actually is it?

5) What conditions do I need to look for, for frost around this time of year, other than temperatures below 0c?

6) What is a trough?

7) How do you forecast and see on a chart, a mild sector?

I will get round to trying to explain them, dewpoint in particular is very inmportant, give me time and I'll drop a pdf link into this thread.

John

Ok, thanks alot John, take your time, I am in no hurry :nonono:

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John my friend you are a legend. Thank you so damn much for your help! I appreciate this so much, and admire your knowledge of the weather.

Please, is there any way I can re-pay you?

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John just having another flick through now, and you said that both of the charts show a trough. How do we see a trough on a model and what is it?

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John just having another flick through now, and you said that both of the charts show a trough. How do we see a trough on a model and what is it?

I'll go into a trough and front, and the difference next time-glad its helping, and of course there is nothing to repay, I enjoy passing on knowledge I learnt when I started out as a meteorologist in 1957 having been a weather enthusiast from about 8 or 9. I just hope that folk don't feel I'm talking down to them.

Next one in a day or so.

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I'll go into a trough and front, and the difference next time-glad its helping, and of course there is nothing to repay, I enjoy passing on knowledge I learnt when I started out as a meteorologist in 1957 having been a weather enthusiast from about 8 or 9. I just hope that folk don't feel I'm talking down to them.

Next one in a day or so.

I don't feel you're talking down to me at all, you're passing on your knowledge at a level I can understand. Obviously if you talked at the level you are familiar with, I wouldn't have a clue what you're talking about. :)

Thanks alot John, :)

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Having talked it over with Paul, apart from the 2nd half of the qu-ans for Backtrack, further ideas on meteorology will be dropped into the general Guides area with the initial link being shown in the most used thread= Model discussion.

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Having talked it over with Paul, apart from the 2nd half of the qu-ans for Backtrack, further ideas on meteorology will be dropped into the general Guides area with the initial link being shown in the most used thread= Model discussion.

Ok John, thank you so much for the effort you are putting into this!

Sounds really good. :D

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Hi guys,

Well it seems alittle silly coming into this thread and asking a question, when there is no one talking about it lmao.

Anyways, i dont understand the models or charts by a long shot, they only thing i tend to look at is the precip charts crap i know. However everyone in the model thread is talking about something coming to far west, what is it? and why do we need it to move back east? and if it moves weast would it still bring widespread snow or just to the eastern side of the uk

cheers for the help :)

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just looking at the metoffice atlantic chart, this must be one of the longest cold fronts I have seen

post-2911-0-72397300-1292630930_thumb.jp

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Hi guys,

Well it seems alittle silly coming into this thread and asking a question, when there is no one talking about it lmao.

Anyways, i dont understand the models or charts by a long shot, they only thing i tend to look at is the precip charts crap i know. However everyone in the model thread is talking about something coming to far west, what is it? and why do we need it to move back east? and if it moves weast would it still bring widespread snow or just to the eastern side of the uk

cheers for the help :)

A low pressure system.

The GFS always over do's lows. Wrapped around a low in a setup like this is snow. So you want the centre of that low as close to you as possible to ensure you get some snow.

Merry Christmas. smiliz64.gif

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Hope someone can help..? Maybe a simple answer that'll get me kicking myself :blush:

I've tried searching this site for an explanation of what a 'shortwave' is... certainly gets mentioned quite a lot on the model discussion thread (I'm still none the wiser and dare not ask there) I'm looking for a visual example ie a chart with one clearly marked on it and some explanation on how they develop, what they are and what they contain that makes everyone talk about them.

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Some good information here:

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Some good information here:

http://forum.netweat...ost__p__1791876

Many thanks Paul for your reply.. I found this within the link you quoted

http://www.theweathe...com/charts/700/

It'll certainly keep me busy for a while - there's certainly more to this than I imagined :rolleyes:

on first glance it looks like a shortwave is a Kink in the isobars... I see my other query mentioned what is a 'WAA".. and there was me thinking it was an enthusiastic abbreviation

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thought i would add this link in, it helps explain the charts in a simple way!

and there is the link to the models from Wetterzentral there to.

http://weatherfaqs.org.uk/node/189 - charts explained

-

main site -

http://weatherfaqs.org.uk/

-

http://weatherfaqs.org.uk/node/144 - this page is for upper air meteorology

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