Forecasting and understanding ULL's

[Cyclonicjunkie]

My knowledge of upper air meteorology is pretty limited and I would like to understand upper level lows better than I currently grasp them.

How do ULL's form?

What causes them to form?

What model graphics do you use to forecast them? 500Mb?

What graphics are used to track them?

Any info regarding ULL's would be greatly appreciated

[Amped]

My knowledge of upper air meteorology is pretty limited and I would like to understand upper level lows better than I currently grasp them.

How do ULL's form?

What causes them to form?

What model graphics do you use to forecast them? 500Mb?

What graphics are used to track them?

Any info regarding ULL's would be greatly appreciated

A low is where the atmospher above you weigths less than average.

A 500mb low is where the atmosphere above 500mb weighs less than average. Usually means a low stratosphere.

Goto this site for more info. We're in storm mode now. wait for the Warminster revenge January thaw to ask more question.

http://www.theweathe...om/habyhints/2/

[Cyclonicjunkie]

A low is where the atmospher above you weigths less than average.

A 500mb low is where the atmosphere above 500mb weighs less than average. Usually means a low stratosphere.

Goto this site for more info. We're in storm mode now. wait for the Warminster revenge January thaw to ask more question.

http://www.theweathe...om/habyhints/2/

Thanks Cheese, I will bump this thread when the torch settles in.

[Confuzzled]

How do upper level lows form?

My limited understanding is too look for areas of speed and directional divergence aloft. When you have more air leaving than coming in you end up with lower pressure aloft.

I always wanted to better understand why upper level lows are offset from their surface counterpart though...

[am19psu]

This has the potential to be a very good teaching thread. Bump it next week after the storm and I (or another met) will try to answer all your questions.

[Rob]

This would be a very good thread to discuss information on. Upper level lows have brought several good snows to the Tennessee area, including last year in West Tennessee. This last snow in Nashville was just that. BNA reported 2.6" of snow while I reported 4" 20 miles away and 6" 25 miles from me west. Favored areas of lift and associated deformation bands would be a good start.

[Confuzzled]

I'll bump this now since I am interested in the topic as well and the storm is a wash.

[thunderman]

How do upper level lows form?

My limited understanding is too look for areas of speed and directional divergence aloft. When you have more air leaving than coming in you end up with lower pressure aloft.

I always wanted to better understand why upper level lows are offset from their surface counterpart though...

Mainly due to the fact that the best horizontal divergence and corresponding lift is located where you have the best Differential Positive Geostrophic Absolute Vorticity Advection (PGAVA) via the Omega equation. This is located ahead of the upper level low. Thus, the height axis tilts UP the thermal wind (you can generally think of the thermal wind as blowing parallel with 1000-500 thickness contours with lower thickness....and cold air.....to the left). Consequently, when the system becomes "stacked" the upper level low has essentially overrun the position of the surface low and thus the surface low is no longer in an area of good differential PGAVA....which reduces upward motion....and low decays as mass accumulates in the column (causing the pressure at the surface to rise). This brings me to an important concept about the synoptic scale, DEVELOPMENT IS FORCED FROM ALOFT!

[thunderman]

here is a descent explanation of the Omega equation and how it works:

http://www.atmos.millersville.edu/~adecaria/ESCI343/esci343_lesson02_QG_omega_eqn.pdf

[baroclinic_instability]

here is a descent explanation of the Omega equation and how it works:

http://www.atmos.mil...G_omega_eqn.pdf

He wants a description of ULL's, not the Quasi-geostrophic Omega equation. Not to mention you should post the Chi equation if you want to talk about the development of ULL's from a dynamic standpoint.

Probably should start with a more basic description since the OP doesn't have a meteorology background.

[thunderman]

He was also asking why the height axis is tilted. I posted the omega equation b/c i referenced it and thought maybe somebody might want to see more about it. I can see where the Chi equation would be of interest too so here it is:

http://www.atmos.millersville.edu/~adecaria/ESCI343/esci343_lesson01_QG_tendency_eqn.pdf

[thunderman]

He wants a description of ULL's, not the Quasi-geostrophic Omega equation. Not to mention you should post the Chi equation if you want to talk about the development of ULL's from a dynamic standpoint.

Probably should start with a more basic description since the OP doesn't have a meteorology background.

My bad, I thought he was a student at Rutgers for some reason. Not sure where I got that from, lol

[Yes_Probably_Maybe_No]

And there I was...in the first grade thinking, "man this addition, subtraction, and math thing is easy"...

[Cyclonicjunkie]

Mainly due to the fact that the best horizontal divergence and corresponding lift is located where you have the best Differential Positive Geostrophic Absolute Vorticity Advection (PGAVA) via the Omega equation. This is located ahead of the upper level low. Thus, the height axis tilts UP the thermal wind (you can generally think of the thermal wind as blowing parallel with 1000-500 thickness contours with lower thickness....and cold air.....to the left). Consequently, when the system becomes "stacked" the upper level low has essentially overrun the position of the surface low and thus the surface low is no longer in an area of good differential PGAVA....which reduces upward motion....and low decays as mass accumulates in the column (causing the pressure at the surface to rise). This brings me to an important concept about the synoptic scale, DEVELOPMENT IS FORCED FROM ALOFT!

Thanks for taking the time to post this, as I do understand most of it and look forward to you maybe explaining in detail how to recognize and understand how ULLS should behave in upper air graphics of global models?????

And there I was...in the first grade thinking, "man this addition, subtraction, and math thing is easy"...

No thanks

[LIsevereWX]

Good stuff to learn! Thanks to those that helped explain things. We should have a separate forum for educational topics. Didn't EUSWX used to have that?

[Cyclonicjunkie]

This has the potential to be a very good teaching thread. Bump it next week after the storm and I (or another met) will try to answer all your questions.

Bump

[Amped]

Uneven heating by the sun or by land sea temperatures and the fact that the earth is rotating (Coriolis force) is the original source of most ULL, though it's hard to trace on a weather map. Terrain also plays a role in creating uneven drag hence vortices.

[am19psu]

My knowledge of upper air meteorology is pretty limited and I would like to understand upper level lows better than I currently grasp them.

1. How do ULL's form?

2. What causes them to form?

3. What model graphics do you use to forecast them? 500Mb?

4. What graphics are used to track them?

Any info regarding ULL's would be greatly appreciated

1. What do you mean by ULLs? Do you mean full latitude troughs? Cutoff lows? Shortwaves? The mechanisms behind them are all different.

2. See 1.

3. Most American meteorologists will use 500mb (roughly, but slightly above, the level of non-divergence), but many European meteorologists prefer 300mb (roughly the level of the jet stream).

4. Any old 500mb graphic will do. Using one that included a vorticity plot will be particularly helpful.

[baroclinic_instability]

1. What do you mean by ULLs? Do you mean full latitude troughs? Cutoff lows? Shortwaves? The mechanisms behind them are all different.

2. See 1.

3. Most American meteorologists will use 500mb (roughly, but slightly above, the level of non-divergence), but many European meteorologists prefer 300mb (roughly the level of the jet stream).

4. Any old 500mb graphic will do. Using one that included a vorticity plot will be particularly helpful.

YES. Europeans destroy us Americans here. We need to analyze differential cyclonic vorticity advection at this level, not at 500 hpa. Multiple studies have confirmed that DCVA (PVA for you old-schoolers) is much more prominent at 300 hpa. The LND is also important, and we often just accept it is around 600 hpa even though it can vary significantly.

[am19psu]

YES. Europeans destroy us Americans here. We need to analyze differential cyclonic vorticity advection at this level, not at 500 hpa. Multiple studies have confirmed that DCVA (PVA for you old-schoolers) is much more prominent at 300 hpa. The LND is also important, and we often just accept it is around 600 hpa even though it can vary significantly.

I can see that mattering quite a bit in the short range and at the mesoscale, but does it make a big difference in the medium range and at the synoptic scale? From a thermal and dynamical point of view, I totally see where you are coming from, but I never understood why Euros got so worked up over this.

[baroclinic_instability]

I can see that mattering quite a bit in the short range and at the mesoscale, but does it make a big difference in the medium range and at the synoptic scale? From a thermal and dynamical point of view, I totally see where you are coming from, but I never understood why Euros got so worked up over this.

In the medium range, most likely not.

In the short-range, I believe it does, and I always believed that incorrect analysis/analyses errors grows rapidly with time. Sooner or later, we have no idea why we are even analyzing what we analyze. In other words, why 500 hpa for DCVA/PVA? What does DCVA/PVA mean? Do the models solve all this non-sense for us? Yes, sort of. As forecasters, we still need to give a probability to an event, and we can't do that unless we analyze what is truly happening (see the "ensemble/deterministic modeling" thread).

"From a thermal and dynamical point of view, I totally see where you are coming from, but I never understood why Euros got so worked up over this."

Sooner or later, we can't allow misconceptions to become the rule. PVA has become a meteorological mainstay, yet it actually is completely incorrect in its meaning. It may seem like a small complaint, but where do we draw the line?

[am19psu]

In the medium range, most likely not.

In the short-range, I believe it does, and I always believed that incorrect analysis/analyses errors grows rapidly with time. Sooner or later, we have no idea why we are even analyzing what we analyze. In other words, why 500 hpa for DCVA/PVA? What does DCVA/PVA mean? Do the models solve all this non-sense for us? Yes, sort of. As forecasters, we still need to give a probability to an event, and we can't do that unless we analyze what is truly happening (see the "ensemble/deterministic modeling" thread).

I've always sort of assumed the answer to this question is because the greatest UVVs should occur near the level of non-divergence from bowstring theory and that's how 500mb became the American standard, but I don't have a better answer than that.

[Cyclonicjunkie]

1. What do you mean by ULLs? Do you mean full latitude troughs? Cutoff lows? Shortwaves? The mechanisms behind them are all different.

Sorry, i'm just now starting to learn upper air stuff and excuse my ignorance, but i'm talking about the type that forms in response to a surface low usually, and I think those would be considered SW's or am I wrong? (they are usually involved with a major trough) And I have been using 500mb absolute vorticity to try an track these, but they seem very badly behaved compared to a surface low.

Is there any way of trying to predict how these will behave, I mean I know how a surface low SHOULD behave but I have no clue to what drives these east or north or south. Also how are the strength of these measured (Just in vorticity?), or what causes one to strengthen or weaken or even disapate etc.

[am19psu]

Sorry, i'm just now starting to learn upper air stuff and excuse my ignorance, but i'm talking about the type that forms in response to a surface low usually, and I think those would be considered SW's or am I wrong? And I have been using 500mb absolute vorticity to try an track these, but they seem very badly behaved compared to a surface low.

Is there any way of trying to predict how these will behave, I mean I know how a surface low SHOULD behave but I have no clue to what drives these west or north or south. Also how are the strength of these measured (Just in vorticity?), or what causes one to strengthen or weaken or even disapate etc.

Can you post a map to show me what you are talking about? Almost always in mid-latitude systems, the surface responds to the upper levels.

[Cyclonicjunkie]

Can you post a map to show me what you are talking about? Almost always in mid-latitude systems, the surface responds to the upper levels.

I must of had that detail confused because I thought that upper levels responded to surface levels, but hey you learn something everyday

Here is the current 500mb av and I see an ULL over North TX is that correct?

[am19psu]

I must of had that detail confused because I thought that upper levels responded to surface levels, but hey you learn something everyday

Here is the current 500mb av and I see an ULL over North TX is that correct?

Using just a 500mb abs. vort. map, you really can't say that is much more than a vort max. Here is a link to the current is the 500mb map. Where you see that vort max in your chart, you'll see a shortwave trough over the TX Panhandle extending to the Rio Grande Valley. Does that make sense to you?

[Cyclonicjunkie]

Using just a 500mb abs. vort. map, you really can't say that is much more than a vort max. Here is a link to the current is the 500mb map. Where you see that vort max in your chart, you'll see a shortwave trough over the TX Panhandle extending to the Rio Grande Valley. Does that make sense to you?

Maybe if the chart wasn't upside down, can you spin it for me? lol But I do see the trough after spinning my cpu upside down.

[am19psu]

Maybe if the chart wasn't upside down, can you spin it for me? lol But I do see the trough after spinning my cpu upside down.

How's this?

[Cyclonicjunkie]

How's this?

Much better, and yes I see the trough.

[am19psu]

Much better, and yes I see the trough.

Ok, so now that we're clear on what we're talking about, what questions do you have about it