A Few Model Related Questions

[Backtrack]

Hi guys, I was wondering if someone can kindly answer a few quick questions I have about John's post made in the model thread about half an hour ago?

For those worrying-needlessly I might add as no one not even Mr Corbyn, have much idea what will happen longer term, take a look at the charts for early November and switch to 20 November>

Have a look at early November 1962 or 1946.

Stop worrying and chasing snowbeams on every run. The weather will do whatever it wants no matter how hard we try and forecast what it should do.

Mild is the key word for a while yet.Nothing in the 500mb charts out to mid November to suggest otherwise apart from the prob of a surface high possibly developing over or near the country giving, depending on cloud cover, some frost and fog overnight.

AO and NAO in the fairly reliable time frame out to 15-20 days are not suggesting much in the way of cold.

MJO and 30mb temp=wait and see at the moment it seems to me?

Regarding the 30mb temp profile. It is my own view with no science to really back it up, other than it has happened on about 3 occasions in the last 3-4 years, IF the temp rises rapidly from where it is within the next 2-3 days then it MIGHT signify colder weather 20-25 days down the line-I said MIGHT and IF?

That's his post right there, my questions are:

1) What are the 500mb anomaly charts?

2) How does reading these charts tell us anything about what our weather might be like?

3) How can I read the charts? (And where if possible?)

4) What is the 'AO' & how can I read it? And where can I find it?

5) What is the 'NAO' how can I read this, and where can I find it?

6) What is the 30mb temperature profile?

7) What influence does the polar vortex and it's positioning have on the UK, and generally, what is the PV?

Really appreciate any answers anyone can give me.

Thanks, Backtrack.

[Isolated Frost]

Hi mate.

The AO is the 'arctic oscillation', the NAO is the 'north american oscillation'. They are basically pressure anomalies (1013mb being 0mb anomaly). Usually a positive AO and NAO means atlantic dominated weather- and usually mild. While negative oscillations can mean cooler weather for us.

The 30mb temperature profile might be the temperature at 30mb (stratosphere), but I'm unsure about that.

http://raleighwx.americanwx.com/models/ecmwf.html

I'm unsure but I think the 500mb charts have something to do with geopotential height/dam and the overall anomaly from the average?

[Backtrack]

Hi mate.

The AO is the 'arctic oscillation', the NAO is the 'north american oscillation'. They are basically pressure anomalies (1013mb being 0mb anomaly). Usually a positive AO and NAO means atlantic dominated weather- and usually mild. While negative oscillations can mean cooler weather for us.

The 30mb temperature profile might be the temperature at 30mb (stratosphere), but I'm unsure about that.

http://raleighwx.ame...dels/ecmwf.html

I'm unsure but I think the 500mb charts have something to do with geopotential height/dam and the overall anomaly from the average?

Thanks Arjan

So by 0mb anomaly, you mean that's normal?

Do positive AO & NAO always mean mild, and the same for negative, do they always mean cold?

By positive and negative, would positive be above 1013mb, and negative below 1013mb?

Where can I find these charts?

Thanks again.

[Costa Del Fal]

Hi mate.

the NAO is the 'north american oscillation'.

Just to clarify im pretty sure the NAO actually means the North Atlantic Oscillation.

[Isolated Frost]

Just to clarify im pretty sure the NAO actually means the North Atlantic Oscillation.

Oops! Yes Luke, my mistake!

[Backtrack]

Oops! Yes Luke, my mistake!

You messing with my brain IF?

[chionomaniac]

Hi guys, I was wondering if someone can kindly answer a few quick questions I have about John's post made in the model thread about half an hour ago?

For those worrying-needlessly I might add as no one not even Mr Corbyn, have much idea what will happen longer term, take a look at the charts for early November and switch to 20 November>

Have a look at early November 1962 or 1946.

Stop worrying and chasing snowbeams on every run. The weather will do whatever it wants no matter how hard we try and forecast what it should do.

Mild is the key word for a while yet.Nothing in the 500mb charts out to mid November to suggest otherwise apart from the prob of a surface high possibly developing over or near the country giving, depending on cloud cover, some frost and fog overnight.

AO and NAO in the fairly reliable time frame out to 15-20 days are not suggesting much in the way of cold.

MJO and 30mb temp=wait and see at the moment it seems to me?

Regarding the 30mb temp profile. It is my own view with no science to really back it up, other than it has happened on about 3 occasions in the last 3-4 years, IF the temp rises rapidly from where it is within the next 2-3 days then it MIGHT signify colder weather 20-25 days down the line-I said MIGHT and IF?

That's his post right there, my questions are:

1) What are the 500mb anomaly charts?

2) How does reading these charts tell us anything about what our weather might be like?

3) How can I read the charts? (And where if possible?)

4) What is the 'AO' & how can I read it? And where can I find it?

5) What is the 'NAO' how can I read this, and where can I find it?

6) What is the 30mb temperature profile?

Really appreciate any answers anyone can give me.

Thanks, Backtrack.

Hi Backtrack - the thing is with metereology I find is that questions lead to more questions, but it is good that you are asking as you will pick up a lot this winter.

Answers to questions:

1&2. 500 mb is a pressure value that is normally found at a certain height in the atmosphere. This height is not fixed. If it is at a greater height than average then we say that it is a positive anomaly and if it is at a lower height than normal then it is a negative anomaly. Hence we can derive an anomaly chart from this. Low heights =troughs. High heights = ridges. Therefore we can deduce from the anomaly charts the placement of the main upper troughs and ridges from these charts.

If someone doesn't beat me to it I will demonstrate this on a chart when I get home.

4. The AO is the Arctic Oscillation which is a measure of pressure differentials between the Arctic and latitudes further south. It effectively measures the strength of the polar vortex. If the AO is positive then the presure differential is increased - ie the polar vortex is stronger with increased jet stream strength. If the AO is negative then the pressure differential is reduced. This is seen when the vortex is reduced with high pressure ridges sitting somewhere in the arctic. The jet stream is slower and tends to be deflected around these ridges - known as high latitude blocking.

5. The NAO is similar in principle to the AO but covers a smaller region - The North Atlantic (not American!!) and so is the North Atlantic Oscillation. The pressure differential readings cover just the North Atlantic and so is very relevent to the UK. Once again a positive NAO suggests an increased differential - ie lower pressure over Greenland /Iceland area, whereas a negative NAO suggestd lower pressure in the mid Atlantic and Greenland higher pressure .

6. 30mb is another pressure reading in the atmosphere but is far higher than 500mb. This pressure is found in the mid levels of the stratosphere and once again the height that this pressure is recorded differs depending on different circumstances. The temperature of the stratosphere is influential in determining how strong the polar vortex is - but you best read the first post of the stratosphere thread for a better idea there!

c

[Isolated Frost]

You messing with my brain IF?

Doesn't take that much!! Just joking of course mate

They don't always mean mild/cold- but are a very good signal.

Positive NAO/AO usually means the flow is normal (we get westerlies) as high pressure is in the normal, atmospherical areas. For negative AO/NAO, we usually need a change in atmospherical conditions, and it's important to watch the Stratosphere thread- and also read chiono and gp's posts.

And here's good old chiono now- there you go!

[Backtrack]

Hi Backtrack - the thing is with metereology I find is that questions lead to more questions, but it is good that you are asking as you will pick up a lot this winter.

Answers to questions:

1&2. 500 mb is a pressure value that is normally found at a certain height in the atmosphere. This height is not fixed. If it is at a greater height than average then we say that it is a positive anomaly and if it is at a lower height than normal then it is a negative anomaly. Hence we can derive an anomaly chart from this. Low heights =troughs. High heights = ridges. Therefore we can deduce from the anomaly charts the placement of the main upper troughs and ridges from these charts.

If someone doesn't beat me to it I will demonstrate this on a chart when I get home.

4. The AO is the Arctic Oscillation which is a measure of pressure differentials between the Arctic and latitudes further south. It effectively measures the strength of the polar vortex. If the AO is positive then the presure differential is increased - ie the polar vortex is stronger with increased jet stream strength. If the AO is negative then the pressure differential is reduced. This is seen when the vortex is reduced with high pressure ridges sitting somewhere in the arctic. The jet stream is slower and tends to be deflected around these ridges - known as high latitude blocking.

5. The NAO is similar in principle to the AO but covers a smaller region - The North Atlantic (not American!!) and so is the North Atlantic Oscillation. The pressure differential readings cover just the North Atlantic and so is very relevent to the UK. Once again a positive NAO suggests an increased differential - ie lower pressure over Greenland /Iceland area, whereas a negative NAO suggestd lower pressure in the mid Atlantic and Greenland higher pressure .

6. 30mb is another pressure reading in the atmosphere but is far higher than 500mb. This pressure is found in the mid levels of the stratosphere and once again the height that this pressure is recorded differs depending on different circumstances. The temperature of the stratosphere is influential in determining how strong the polar vortex is - but you best read the first post of the stratosphere thread for a better idea there!

c

Wow thanks so much for such a detailed response chionomaniac. I didn't fully understand everything in there, but I'll read over it 10 more times to get it into my head, I'm sure I will then!

Could you tell me what influence does the polar vortex and it's positioning have on the UK, and generally, what is the PV?

Also, am I right in thinking that a negative NAO would lead to blocking in the Atlantic due to increased pressure over Greenland? Obviously a block isn't always the case, but would we generally need a negative NAO for a block to be established?

Again, thanks so much, I really appreciate that.

Doesn't take that much!! Just joking of course mate

They don't always mean mild/cold- but are a very good signal.

Positive NAO/AO usually means the flow is normal (we get westerlies) as high pressure is in the normal, atmospherical areas. For negative AO/NAO, we usually need a change in atmospherical conditions, and it's important to watch the Stratosphere thread- and also read chiono and gp's posts.

And here's good old chiono now- there you go!

How dare you! :lol:

Thanks for that too. I would read GP's posts, but I've gotta be honest, I don't understand a word he says. He's a meteorological genius.

[Isolated Frost]

Chiono is reading the topic- so he will have a brill answer coming up- but for it's worth:

The polar vortex is a elongated shaped cyclone in the arctic (well the northern hemispherical one is)... it's positions are usually baffin island canada and ne siberia. They are positioned in the upper troposphere and stratosphere. A strong pv usually contains all the cold air in the arctic- but when it moves south, and/or weakens, usually cold seeps south.

Take 16 dec 2010 for example. that low to the ne is part of the polar vortex. it let the arctic floodgates open for deep cold to reach the uk.

*waits happily for chiono's correct answer*

[Backtrack]

Chiono is reading the topic- so he will have a brill answer coming up- but for it's worth:

The polar vortex is a elongated shaped cyclone in the arctic (well the northern hemispherical one is)... it's positions are usually baffin island canada and ne siberia. They are positioned in the upper troposphere and stratosphere. A strong pv usually contains all the cold air in the arctic- but when it moves south, and/or weakens, usually cold seeps south.

Take 16 dec 2010 for example. that low to the ne is part of the polar vortex. it let the arctic floodgates open for deep cold to reach the uk.

*waits happily for chiono's correct answer*

Well this is certainly one of the more easy to understand subjects, cheers for that.

What happens if the PV is in a bad position? E.G far West of Greenland?

[chionomaniac]

Could you tell me what influence does the polar vortex and it's positioning have on the UK, and generally, what is the PV?

Also, am I right in thinking that a negative NAO would lead to blocking in the Atlantic due to increased pressure over Greenland? Obviously a block isn't always the case, but would we generally need a negative NAO for a block to be established?

No problem, b.

First, the polar vortex (PV) is a large vortex or cyclone centred around the north or south pole that extends from the middle layers of the troposphere way up into the stratosphere. It is very strong and powerful and sets up in winter when the polar temperatures drop creating a large temperature and pressure differential between the poles and latitudes further south. The vortex is demarcated by the polar front jet stream to the south. The stronger the polar vortex, the stronger the jet stream becomes and tighter to the pole - a classic positive AO signature.

What we like to see is a disrupted or weakened polar vortex during winter with resultant high latitude blocking such as the Greenland high. A high pressure or upper ridge over Greenland would lead to a negative NAO as you suggest. The negative NAO is formed as a result of the decreased pressure differential and is not a something that drives it.

[Isolated Frost]

Well this is certainly one of the more easy to understand subjects, cheers for that.

What happens if the PV is in a bad position? E.G far West of Greenland?

The Pv is usually elongated, and so is in two locations at one (take now, nw siberia and just nw of the canadian arctic).

I'm not sure about if the PV is in west greenland (or west of greenland), regarding our weather.

good post chiono aswell

[chionomaniac]

Chiono is reading the topic- so he will have a brill answer coming up- but for it's worth:

The polar vortex is a elongated shaped cyclone in the arctic (well the northern hemispherical one is)... it's positions are usually baffin island canada and ne siberia. They are positioned in the upper troposphere and stratosphere. A strong pv usually contains all the cold air in the arctic- but when it moves south, and/or weakens, usually cold seeps south.

Take 16 dec 2010 for example. that low to the ne is part of the polar vortex. it let the arctic floodgates open for deep cold to reach the uk.

*waits happily for chiono's correct answer*

Your answer is correct as well and a lot quicker!!

Backtrack you are touching on getting to grips with the fundamental meterology here that affects our country. I found it very difficult to visualise first time around. Here is a site full of answered questions - but for an American audience.

http://www.theweatherprediction.com/habyhints/

[Backtrack]

No problem, b.

First, the polar vortex (PV) is a large vortex or cyclone centred around the north or south pole that extends from the middle layers of the troposphere way up into the stratosphere. It is very strong and powerful and sets up in winter when the polar temperatures drop creating a large temperature and pressure differential between the poles and latitudes further south. The vortex is demarcated by the polar front jet stream to the south. The stronger the polar vortex, the stronger the jet stream becomes and tighter to the pole - a classic positive AO signature.

What we like to see is a disrupted or weakened polar vortex during winter with resultant high latitude blocking such as the Greenland high. A high pressure or upper ridge over Greenland would lead to a negative NAO as you suggest. The negative NAO is formed as a result of the decreased pressure differential and is not a something that drives it.

Right! Thank you so much again!

I've gotten my head around the NAO now. I think that's sunk in pretty well

So for cold it would be desirable to have a weak PV. By weak is there a specific reading that is the cut off point for strong and weak? And do I need to be a Net Weather extra subscriber to view the chart for it? I only have the radar unfortunately.

Your answer is correct as well and a lot quicker!!

Backtrack you are touching on getting to grips with the fundamental meterology here that affects our country. I found it very difficult to visualise first time around. Here is a site full of answered questions - but for an American audience.

http://www.theweathe....com/habyhints/

This will come in very handy too, will have a good read of that now, thanks!

[chionomaniac]

So for cold it would be desirable to have a weak PV. By weak is there a specific reading that is the cut off point for strong and weak? And do I need to be a Net Weather extra subscriber to view the chart for it? I only have the radar unfortunately.

This is where it gets a little trickier to explain. We said earlier that the level or height in the atmosphere at which the pressure 500mb can be measures differs. Another way of looking at this is that we can measure upwards from sea level to the level at which the height is 500mb - also known as the geopotential height. This height value fluctuates depending upon the strength of the polar vortex - the lower it resides the stronger the polar vortex. This brings us nicely to the most common chart seen on nw - the 500mb hgt chart.

The height at which the 500mb is measured is indicated by the colours of the chart with the polar vortex induced lower heights being indicated by the blues and purples.

So these colours don't indicate temperature or surface pressure but the geopotential height at which 500mb is measured and the stronger the polar vortex the darker the colour

[Backtrack]

This is where it gets a little trickier to explain. We said earlier that the level or height in the atmosphere at which the pressure 500mb can be measures differs. Another way of looking at this is that we can measure upwards from sea level to the level at which the height is 500mb - also known as the geopotential height. This height value fluctuates depending upon the strength of the polar vortex - the lower it resides the stronger the polar vortex. This brings us nicely to the most common chart seen on nw - the 500mb hgt chart.

The height at which the 500mb is measured is indicated by the colours of the chart with the polar vortex induced lower heights being indicated by the blues and purples.

So these colours don't indicate temperature or surface pressure but the geopotential height at which 500mb is measured and the stronger the polar vortex the darker the colour

Okay I think I get the height measuring. So the colours don't indicate the pressure gradient, just the height in which the PV is being measured?

Am I right in thinking that higher pressure over the Arctic will lead to a weaker PV making it more beneficial to cold fans in Winter?

Also, one more question (sorry, I'm such a noob), I've just read that the PV usually stays in between the Baffin Islands and Canada, is what I've circled the PV? If so, why is it over Russia?

[Isolated Frost]

Okay I think I get the height measuring. So the colours don't indicate the pressure gradient, just the height in which the PV is being measured?

Am I right in thinking that higher pressure over the Arctic will lead to a weaker PV making it more beneficial to cold fans in Winter?

Also, one more question (sorry, I'm such a noob), I've just read that the PV usually stays in between the Baffin Islands and Canada, is what I've circled the PV? If so, why is it over Russia?

On wiki it says Baffin island and NE Siberia. Baffin island is part of Canada

[Backtrack]

On wiki it says Baffin island and NE Siberia. Baffin island is part of Canada

Oh right. I must of mis-read then.

I'm good at geography but I've never heard of Baffin Island.

To be beneficial to us, would we want the PV directly North of the UK?

[Isolated Frost]

Oh right. I must of mis-read then.

I'm good at geography but I've never heard of Baffin Island.

To be beneficial to us, would we want the PV directly North of the UK?

maybe a touch to the north east;

Bloody weather porn that is!

[Backtrack]

maybe a touch to the north east;

Bloody weather porn that is!

Haha, we can only dream of charts like that this year.

[chionomaniac]

Okay I think I get the height measuring. So the colours don't indicate the pressure gradient, just the height in which the PV is being measured?

Am I right in thinking that higher pressure over the Arctic will lead to a weaker PV making it more beneficial to cold fans in Winter?

Also, one more question (sorry, I'm such a noob), I've just read that the PV usually stays in between the Baffin Islands and Canada, is what I've circled the PV? If so, why is it over Russia?

Yes you have circled the heart of the PV.

The PV normally starts the winter in two segments with the main segment situated over the cold plains of northern Siberia (the other segment over Baffin but certainly not as guaranteed as the Siberian segment). As winter progresses the PV becomes more centrally placed in the Arctic. Of course the position of the PV is not fixed and can be split up into numerous vortices.

[Backtrack]

Yes you have circled the heart of the PV.

The PV normally starts the winter in two segments with the main segment situated over the cold plains of northern Siberia (the other segment over Baffin but certainly not as guaranteed as the Siberian segment). As winter progresses the PV becomes more centrally placed in the Arctic. Of course the position of the PV is not fixed and can be split up into numerous vortices.

Wow this is really interesting stuff. Thanks again for your replies

Do you have any idea where I can find the current states of the AO and NAO.

[knocker]

Wow this is really interesting stuff. Thanks again for your replies

Do you have any idea where I can find the current states of the AO and NAO.

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/ao.shtml

[Backtrack]

http://www.cpc.ncep...._index/ao.shtml

Thanks WS

Jesus these look hard to understand.... :o

Right, so looking at those NAO charts, am I right in thinking that we've gone from a negative NAO to a positive NAO from the start of October?

Not a strong +NAO though?