The Novice's Chart Thread

[SMU]

Hi Daisy/All-

Ive got a spare while at work- so I will put a few things down- its off the bat, and I appologise for any errors/typo's etc-

I suppose before we go into teleconnection an educated understanding of what it all means- for example Im not a baker- but I know what a good loaf of bread tastes like-

So with that in mind Teleconnections are measures & variations of the Sea surface temperatures and atmospheric Pressure-

The reason the teleconnections are called oscillations are because at regular intervals they the components of their make up are predisposed to a certain state-

The teleconnections are as follows-

SST' driven are-

ENSO- El nino Southern oscillation- ( the actual measure though in terms of reference & forecast is the SOI)

PDO- Pacific Decadal oscillation

Atmospheric Pressure Driven

AO- Artic oscillation

NAO- North Atlantic Oscillation

QBO- Quasi-Biennial Oscillation

MJO- Madden-Julian oscillation

PNA-Pacific/North American

( for reference to the QBO read GP's pacific pointers thread)

It would probably take hours & hours to describe them ALL- however its all very similar to a tug of war-

Lets assume we have on one side a Cold UK winter & on the other a MILD UK winter-

THE winner of the tug of war will be the combination of the teleconnections which predisposes the atmosphere towards- either warm or cold-

* NB: what is cold for the UK MAY not mean cold for the other areas of the GLOBE-

You would think that way forwards is to put into rank order the teleconnections that MOST apply to OUR neck of the woods- However its not that straight forward- ALL of them are interlinked and often Mute another-

The 'classic' Teleconnection is the El nino - IF this is positive in a big way ( Or negative La nina) it has massive effects on global circulation patterns- This isnt really the thread for going in depth on this one- BUT it is NEUTRAL this season & has NO further effects-

Many people fall into the trap of viewing the UK under the microscope- interms of looking at patterns over the atlantic BUT thats TO narrow a viewpoint-

EVERYTHING starts in the pacific & works its way EAST- firstly manifesting in America & then down the line to the UK-

So this i why we look upstream to see developments-

I suppose the way to gradually increase knowledge here is to NOT try to understand each & every one, but develop knowledge on ONE subject that be the Jet stream-

The reason I say this is All the above oscillations are are measures measures of anomlies-

If you havent got a sound base of knowledge on these to make the jump from these measures to forecast then the best thing to do is work your way back from a common denominator-

That be the jet stream-

At the end of the day when all said & done the END result of the teleconnections working in harmony provides us with the likely position of the jet stream-

I hope there is a little knowledge here from the readers point of view-

but once we can get a definative steer on jet stream location ALL forecasting becomes a hell of a lot easier-

With a base knowledge of this, but studying the continued locations of the jet stream & strength you can work backwards and make assumptions about the phase of the teleconnections-

So I would when studying the charts ( and anyone for that matter) make a POINT of looking at the 200's & 300 Mb charts for the jet stream-

Click this link And goto Northern Hemisphere then 200Mb charts

Understanding this is Key-........

Below is a few teleconnection pointers-

AO- the mean pressure differential between the pole & the Equator-

When Strongly negative it indicates that there is High lattitude blocking & low pressures taking a southerly track around the globe-

This is GOOD news for the UK getting cold as we do need high lattitude blocking to our North to send the cold air south

Even though the AO MAYBE sharply negative the UK can still be on the mild side- as the Negativity of the AO may only apply at that point the Pacific

I mentioned this earlier though ( and forgive me for going a little statistical again)

there is a linear correlation between the AO & NAO being Negative -

Linear correlation is basically a statement regarding how well 2 parties associate with one another-

+1 being they match perfectly 7 Work in tandem, 0 meaning they have NO direct impact,

and -1 would be they are opposite-

A Classic -1 Linear correlation would be an icelandic Low & a Negative NAO- it doesnt happen-

However the correlation between negative AO & negative NAO is ~ 0.6+- which means once the AO is neg it is often ( but NOT always long before the NAO follows)

The NAO- probably the most talked about teleconnection on the forums-

Remember all the measure is is the pressure differential between ~ the Azores & iceland

Its almost IMPOSSIBLE to get very cold with a positive NAO-

but there are manifestations of both neutral & negative that can provide the UK with the Bitter Stuff-

The 'Classic' NAO in everyones imagination is the Greenland High and low pressure to our South East giving that Cold feed-

However cast your mind back to the Armagedden charts of last nights 18z and that was a Neutral NAO because there was A high pressure just to the NW of the UK but LP over Iceland & low pressure to the SE- so the differential was LOW-

I think the term Negative is after a measurement of -1 NAO if you are every checking the links-

With reference to the above 2 teleconnection- there are LOTS of manifestations of the 'blocking' which is the pre-requsite for Cold for the UK- and so occasionally these 2 arent great at demonstrating cold if they show as Neutral-

The PNA is another differential measure of Pressure between the coasts of America-

What forecasters do when observing this is look for phases of the PNA- either +ve or –VE to demonstrate the Strength of the jet stream-

If the PNA is big +VE then that indicates there is a large amount of blocking, and this should then replicate downdstream-

However there is a NOT im afraid a direct correlation with +VE or –VE PNA to UK Cold- its just something that is a HELPFUL GUIDE-

Similar to the NAO the PNA has MANY MANY manifestations and unless again you have had experience of them all it would be hard to place a forecast just based on little experience-

The PDO-

Measures the Sea surface temperature anomalies in the North west Pacific- Some people would find it strange that this region is measured & in particular how it effects the UK But… again the Negativity or Positivity has a marked effect on the Jet stream into the Pacific North west of America-

The more NEGATIVE it is the Stronger the Pacific Jet is-

So there- ive summarised them for the best part- they all have a meaning- however with limited knowledge my suggestion is an overview for knowledge purpsoes rather than indepth knowledge-

The way forwards to ANY beginner/Novice perhaps intermediate is to spend time looking over the Jet stream patterns- that CANNOT be emphasized enough-

The location Jet stream is as I said at the start the Net result if all the PUSHING/PULLING, STRENGTHENING/WEAKENING that the teleconnections exert on it-

When looking at the runs of the models spend as long as possible on the 200’s & 300’s, they tell the story before its even happened-

Key 2 Phrases on Jet stream are-

Zonal & Meridional-

Zonal refers to a jet that is WEST to EAST & STRONG - NOT good for cold weather fans-

Meridional refers to the jet that is NORTH to SOUTH & Weak- good indicators to cold for the uk…..

Best regards

Steve

Edited January 4, 2006 by Steve Murr

[BrickFielder]

Excellent post Steve.

Jet Streams in very simple terms are fast moving ribbons of air which seperate cold air to the north and warm air to the south and are found at the upper level of the troposphere (the troposphere is where our weather is ,above which is the stratosphere). Being to the north of the jet usually means cold weather. There is a kind of feed back mechanism between the jet and weather patterns. Where there are bursts of energy (streaks) along the jet due to high temperature differences, this is where weather systems form (both low and high pressure at entrance and exit regions). These weather systems then modify the jet by moving air so that high temperature contrasts occur somewhere else (forming a new streak).

This is all tempered with surface temperatures over land and sea creating different temperature air masses which tend to direct the jet in certain directions (up around warm) This is why the azores high is a regular feature in winter out over the warm atlantic ocean with sea temperatures much slower to cool down than land temperatures. This is all further tempered by weather systems causing waves which very slowly bounce out up into the stratosphere and back down again to affect the jet and weather systems below.

I will stop there before I get complicated.

Just to say that ignoring the polar nightime jet that the jetstream ribbon circulates the world so the pacific jet is the same one as we get here.

Probably one of us will talk later about

the walker,ferrel and hadley cells

the subtropical jet and polar front jets

weather fronts and the jetstream

how to predict high and low pressures from a jet forecast and understand ridging and troughing.

[johnholmes]

thanks both of you, all good stuff.

Regarding the link between jet streams and developing low and high pressures, that is already available in our Guides. I did also do a tutorial trying to show how what left entrance and right exits mean to a developing system of low pressure. Remember back to the last really rapid low deepening in the Atlantic, some time later in the autumn I think? Off the top of my head I cannot remember the date. It is available somewhere and I'll dig it out. When I ge time I will tidy it up and put it in the Guide section

regards

John

[Daisy]

Thanks very much all for your time and effort.

I now need to read several times and digest all the information, so much to learn. I find this really fascinating and really do apprecitate the help I have been given. Good thread Smich!

I was wondering if there was a magazine on "meterology for the lay person". I bet it would sell loads in this weather obsessed nation. Maybe a future business idea for you experts?! :blink:

Best regards

Daisy

[BrickFielder]

Yes lots of good information in the current guides.

The Netweather guides

Here is a couple of extra educational links to do with the jetstream.

Upper Air Meteorology

What goes on aloft

Edited January 5, 2006 by BrickFielder

[smich]

Right, finally had time to properly read thru Steve's and BF's posts.

What a revelation (no not Steve M writing in plain English for once! :lol: )

I think half of my problem with the jetstream in particular was that I'd forgotten there was still atmosphere BETWEEN the jets - they are merely a concentration of activity in a very chaotic environment where the only given is the earth spins!

I know see how the oscillations are truly a force to be reckoned with when they correlate in the right way. These seem to be the driving force of the weather closer to the surface.

Given last months conflict re SST's and Prospects for winter, it's interesting to note that the NAO is not driven by SST's...

Thanks guys, and as for Hadley Cells - I actually came across these helping my wife with the Planetary Science element of her degree........but I haven't heard them mentioned once on the Net weather forums!

Thanks again

Smich

[smich]

Hello again! Thought I'd keep things moving along here, so I'm going to go off on a different (but topical) track...

Much has said in the models threads recently about those who take one run and make hasty decisions without checking out what trends are actually appearing. It is actually recommend by virtually all the forecasters here to study one run and compare each days charts as this is the best way to spot trends. On John Holmes' advice I decided to start saving 06z charts to see what might "appear".

It takes some effort and patience, but it's worth it! Here is a simple illustration of how it works: I'm going to post 3 charts (edit - 2charts and a link!). All predict what the GFS thinks will be happening at 6am on Saturday 14th Jan 2006. The first chart was saved on Saturday:

The second chart was saved on Sunday:

sundays_forecast_for_14jan06z.bmp

Compare the two. Despite being virtually out in Fantasy Island, they are remarkably similar - High pressure dominates Scandinavia, Central and Eastern Europe and even the mid Atlantic. The small high pressure over Greenland is surrounded by little low pressure systems also. But there is one BIG difference - yup the large deep low pressure off the NE of Newfoundland is significantly downgraded, and positioned much further south. Also, the low to the east of Iceland is now further south and west and has taken on an oval North/South shape. Here is the third chart which I saved today(Monday):

More changes, some very subtle. The big deep low is now "confirmed" as being much weaker, and see how the low to the SW of Iceland is now even further south and west - nearly in the middle of the Atlantic! This allows an extra ridge of high pressure to push Northwards to the east of it , strengthening the scandinavian/european high...

Now check out the top right hand corner of all three charts. In the first, there is a small area of high pressure poking it's nose into the picture from the top - it's almost directly above the Scandinavian high and trying to link up with it. In the second, it has moved further south (you can now see the "H") and it is a little nearer. In todays chart the isobars are now virtually touching. I wonder if tomorrow the two will have connected...?

Well, these are the trends I THINK I've been spotting! They tell me that the atlantic might get quieter, that low pressure systems are likely to be further south and that the high pressure over europe and scandinavia might stretch westwards ("retrogress"). This is all good if you like cold btw!

Hope this is useful for some of you, sorry it's a bit poorly done. I'm an amateur afterall! And for any of the experts popping in, please tell me if I'm picking up trends incorrectly ! :o

Keep 'em peeled!

Smich

Edited January 9, 2006 by smich

[smich]

Rather than provoke any arguing on the models threads, I'm going to post todays 06z here. Don't forget, we are now looking at just 96 hours til Sat 6am...

tuesdays_06z.bmp

I'm must confess I'm puzzled now. There is a major change as far as I can see - low pressure has suddenly spread eastwards, completely blocking the High Pressure from linking up, north of Scandinavia.

Either GFS has picked up a new signal that warrants this change of heart, or I've been chasing shadows/talking complete hogwaDoh a dumb swear filter got the better of me

This is presumably the kind of change that is causing such strange charts at the moment?

rgds

A Puzzled Novice

[armleyred]

Hello everyone

I have a question as i'm trying to understand the charts albeit very slowly i have a quick question. On the last few GFS runs, Low pressure splits our high pressure moving throught Scandinavia, my question is after this passes through why doesn't pressure rise allowing a link up of our high pressure with the Russuian one? Is this because of the slow moving nature of the low pressure or is it due to the strength of the jet stream?

Cheers Gareth

[Thundery wintry showers]

Someone with more knowledge of modern-day meteorology than me might be able to answer that one, but I don't have a clue, and I'm not sure that anyone else does, for that matter!

Normally, one would expect the two highs to link up, maybe not immediately, but certainly that would be odds-on to happen within a week or so. The fact that it hasn't done is probably not unprecedented, but certainly goes against the "rules" of meteorology.

[BrickFielder]

Well lets have a quick look at a jetstream chart at +48hours.

Notice how low pressure systems form along the jetstream at the right entrance and left exit from a jetstreak (jetstreak is a fast moving part of the jet). Notice how the high pressure forms in the arch between the jetstream.

Lets now look at a mid level temeprature chart.

Notice how the boundary between cold and warm air is where the jetstream was on the previous chart. Now look at the where the low pressure is coming down over scandinavia. This dragging cold air south which will force the jetstream south and a little east. Here is the lower level chart to go with the mid level one and you can see more cold air is dragged south at this level.

So the answer is the high pressure does not reform because the jet moves in behind and it moves in behind because cold air has been brought south.

From this you should gather that low pressure systems form around the jet, but those low pressure systems once created change the jet.It is a lot more complicated than that with sea surface temperatures, snow cover ,mountains, wave properties all coming into play but you might get the general idea.

Here are some more charts from a little further on. These also illustrate how the jet reflects the boundary of cold and warm and notice how the low off Labrador wraps up the warm air round it bringing warm air north.There will always be warm air in the mid atlantic because the sea does not cool down from the summer as quickly as the land and thats why we tend to have mild weather in the UK.

[smich]

Hi everyone! Keeping the thread alive and all that...

...ever wondered what an "outlier" was? As I understand it, the GFS charts we look at represent the operational run, and other runs are calculated at the same time, with adjustments made for flawed data etc. These runs are all referred to as "members".

Occaisionally, the operational run is completely at odds with all the other members. Finally, I have a good example:

When this type of chart appears, a lot of experienced members here will say it should be "binned".

It's obvious why!

Cheers pop-pickers!

Smich

[John Cox]

Hi everyone! Keeping the thread alive and all that...

...ever wondered what an "outlier" was? As I understand it, the GFS charts we look at represent the operational run, and other runs are calculated at the same time, with adjustments made for flawed data etc. These runs are all referred to as "members".

Occaisionally, the operational run is completely at odds with all the other members. Finally, I have a good example:

When this type of chart appears, a lot of experienced members here will say it should be "binned".

It's obvious why!

Cheers pop-pickers!

Smich

Hi Smitch,

Well put.

An Outlier is one that is odds with the rest of the members. In other words, if the control run shows the warmest temps compared to the rest of the "members" then it is a "warm" Outlier. In other words "It is less likely" to be the warm result it is showing.

Hope this helps.

Edited January 25, 2006 by John Cox

[acbrixton]

Re outliers: here is a pm to John Holmes and his response:

John may I please trouble you for some guidance.

I have often mused as to precisely what test is applied to the ensembles when the term "outlier" is used (either regarding the control run, or more rarely, other runs)

It seems to me that there may be several ways of tackling this:

1. There is no strict definition in that "outlier" is not a formally defined term (rather like "Bartlett" it is no more than an informal but useful shorthand term) and thus requires an exercise of subjective judgement with the inevitable result that there may properly be disagreements as to the application of the term in border line cases.

2. There is a precise mathematical formula applied e.g. a particular run is [x c] above or below the mean or some other benchmark.

3. There is the test applied by TEITS and Kold Weather (apropos the 00z London ensemble where I described the control run at the end of the period as a "considerable cold outlier") where if a run is "supported" (i.e, I assume, other runs at various times show a similar value) then there can, by definition, be no outlier. If this is the case how many other runs' support is required and over what period?

Sorry to make a meal out of this (but what do you expect from a lawyer...)

Many thanks

kind regards

Andrew

hi Andrew

Sorry I'm so late with any reply. I saw it early yesterday and then forgot about it!

I'm no expert on Ensembles but am not aware of any objective guidance. This is the best I can do and was posted by Paul a short time ago.

http://www.net-weather.co.uk/forum/index.php?showtopic=25663

hope it helps

regards

John

[smich]

thanks for your extra input John and acb.

It was so hard for me to spot a true outlier - the vast majority of runs have operationals that are "mild" or "cold", but they don't don't really deviate from the vast majority.

When I saw that one, I thought "Blimey! THATS an outlier!"

Smich

[Hairy Celt]

thanks for your extra input John and acb.

It was so hard for me to spot a true outlier - the vast majority of runs have operationals that are "mild" or "cold", but they don't don't really deviate from the vast majority.

When I saw that one, I thought "Blimey! THATS an outlier!"

Smich

Time and place to resurrect this one...

Seems to me that outliers are often identified by folk by looking at the ensemble plots - a member that's out on its own is, by some subjective criteria, called an outlier. Fine, but unless you have the tools to investigate why a member is out on its own, it's pretty meaningless. I've not been able to discover how the GFS data is varied to produce the different runs, and even if I had, I may well not make much sense - cos I'm not a serious student of meteorology!!! So, my point is, without some further interpretation, the ensembles aren't really very helpful to novices other than to see that there's either good agreement or lots of scatter. Maybe that's all we want though. Okay, midnight ramble over...

Edited February 11, 2006 by Hairy Celt