Winter 2023/24 - Discussions & Forecasts

[MattStoke]

6 minutes ago, Met4Cast said:

Nope, it's the other way around. 

A more energised jet stream allows bigger peaks and deeper troughs compared to a more sluggish jet stream which is why we tend to see the jet stream be a lot more "wobbly" in winter and much "straighter" during summer. Stronger jet streams lead to stronger anticyclonic wave breaking events. 

I believe that's the CFS.

That is the complete opposite to reality - 

The Jetstream - What It Is and How It Affects Our Weather - Netweather.tv

WWW.NETWEATHER.TV

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Learn about the jet stream - what it does and how it affects our weather.

 

[Met4Cast]

3 minutes ago, MattStoke said:

That is the complete opposite to reality - 

The Jetstream - What It Is and How It Affects Our Weather - Netweather.tv

WWW.NETWEATHER.TV

---

Learn about the jet stream - what it does and how it affects our weather.

 

I'm sorry but I'm 99% you are incorrect on this. 

Think of the ocean, large waves require more energy in the system not less, big waves have far higher peaks and far deeper troughs compared to a calm ocean, the same principle applies to the jet stream. To get a highly amplified jet stream (and thus, areas of blocking & troughs) you need energy injected into it, it's the exact reason why you see a far more amplified jet stream in the winter compared to the summer. 

The jet has more energy in winter due to the thermal temperature difference and thus is able to be more amplified compared to the weaker energy during the summer.

[sundog]

Surely a fired up jet stream is bad for the chance of cold spells and a sluggish one is better.  For example when the eastern states get a cold spell that can fire up the jet across the Atlantic bringing us plenty of rain and little cold.

[Met4Cast]

Just now, sundog said:

Surely a fired up jet stream is bad for the chance of cold spells and a sluggish one is better.  For example when the eastern states get a cold spell that can fire up the jet across the Atlantic bringing us plenty of rain and little cold.

Yes, but that's more regional, I'm talking on a hemispheric scale. A sluggish jet stream tends to be flatter overall across the hemisphere and therefore with smaller peaks/troughs you get less amplification, i.e mid latitude blocks rather than high latitude blocks, if it's cold you're after then the latter is what you need.

[SqueakheartLW]

14 minutes ago, Met4Cast said:

Nope, it's the other way around. 

A more energised jet stream allows bigger peaks and deeper troughs compared to a more sluggish jet stream which is why we tend to see the jet stream be a lot more "wobbly" in winter and much "straighter" during summer. Stronger jet streams lead to stronger anticyclonic wave breaking events. 

I'm sure that when the jet is strong it typically gets much flatter.

The winters of 2013/14 and 2019/20 both had a strong and flat zonal flow. Many times the jet got up to 200mph. The flat, zonal jet had more energy due to the stronger polar vortex and there was little to no amplification of the jet.

The same principle applies in rivers where the fast flowing parts are generally fairly straight whilst the slow areas have meanders.

In contrast winters of 2009/10 and 2012/13 had a much slower and therefore less energetic jet stream. Both of these winters featured frequent amplification and northern blocking as a result due to a weaker polar vortex.

[CoventryWeather]

23 minutes ago, MattStoke said:

A more energized jet stream is less amplified, not more. It's a weaker jet stream that allows mid to high latitude blocking high pressure to set up.

I'm not a professional, but I think they can both lead to blocking patterns. A weaker jet in summer for instance amplifies the highs towards Europe, and a strong jet can deepen the trough and ridges, thus making the pattern amplified. 

I normally like to think about it like a tropical low influencing things, as soon as the low gets influenced by the jet, it strengthens it and cause a huge ridge and trough scenario. 

Hopefully I've gotten that right :/

[MattStoke]

I feel like I've gone into a parallel world.

Jet stream is weaker and more amplified (meridional) in summer due to less of a thermal gradient than in winter when the opposite is true. Blocking high pressure and wave breaking the occurs more frequently in summer and when the jet stream is weaker. Conversely, a greater thermal gradient that occurs in winter leads to a stronger and more zonal jet stream with fewer incidents of blocking high pressure.

This has always been the case in every related weather report, study, professional meteorological video forecast, the Fundamentals of Meteorology uni course I studied, etc etc etc. 

5 minutes ago, CoventryWeather said:

I'm not a professional, but I think they can both lead to blocking patterns. A weaker jet in summer for instance amplifies the highs towards Europe, and a strong jet can deepen the trough and ridges, thus making the pattern amplified. 

I normally like to think about it like a tropical low influencing things, as soon as the low gets influenced by the jet, it strengthens it and cause a huge ridge and trough scenario. 

Hopefully I've gotten that right

A stronger jet stream will deepen troughs but not allow (or at least make it more difficult for) blocking areas of high pressure to develop and be maintained. 

Edited October 26, 2023 by MattStoke

[CoventryWeather]

1 minute ago, MattStoke said:

A stronger jet stream will deepen troughs but not allow (or at least make it more difficult for) blocking areas of high pressure to develop and be maintained. 

Deeper trough leads to more warm advection. Wouldn't that lead to stronger highs? 

Regardless on whether the high gets maintained, it's still an amplified jet stream in my view - doesn't necessarily need to be long lived.

Again, may be wrong - the stuff you are saying makes complete sense. Would have thought the above makes sense? 

[MattStoke]

What is the jet stream?

WWW.METOFFICE.GOV.UK

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The jet stream is a core of strong winds around 5 to 7 miles above the Earth’s surface, blowing from west to east.

 

[Met4Cast]

21 minutes ago, CoventryWeather said:

I'm not a professional, but I think they can both lead to blocking patterns. A weaker jet in summer for instance amplifies the highs towards Europe, and a strong jet can deepen the trough and ridges, thus making the pattern amplified. 

I normally like to think about it like a tropical low influencing things, as soon as the low gets influenced by the jet, it strengthens it and cause a huge ridge and trough scenario. 

Hopefully I've gotten that right

Correct. The idea that you can have deeper troughs in a more energised jet stream but not more amplified highs is bizarre, that would go against the laws of physics unfortunately. For every action there is an equal and opposite reaction. Deeper troughs mean that somewhere an amplified high must also exist. That's just basic meteorology 101.

+AAM which is often the result of +FT or +MT events essentially take energy from the rotation of the earth and transfers it into the atmosphere which leads to stronger westerlies within the overall wind budget, this in turn leads to a more disturbed jet stream (due to the injected energy). These disturbances then travel across the planet in an easterly direction leading to deeper troughs and more amplified highs. 

What you're saying is absolutely right. A strong jet stream in the Atlantic, it's true, often leads to flat zonal patterns, however I think people are confusing localised phenomena with the hemisphere. I'm talking about the energy in the overall system. 

A feature of El Nino is stronger westerly trade winds in the Pacific. There's a reason blocking is more likely during El Nino years and that reason is added westerly energy into the overall windflow budget.

Edited October 26, 2023 by Met4Cast

[MattStoke]

It's "basic meteorology 101" that a stronger jet stream is more zonal, and a weaker one more meridional and occurs more in winter than in summer due to an increased thermal gradient in the former. I cannot believe this is even being debated. Just bizarre. 

Edited October 26, 2023 by MattStoke

[Methuselah]

2 minutes ago, MattStoke said:

It's "basic meteorology 101" that a stronger jet stream is more zonal, and a weaker one more meridional and occurs more in winter than in summer due to an increased thermal gradient in the former. I cannot believe this is even being debated. Just bizarre. 

Such basic physics also explains why slow-moving streams meander, whereas fast-moving ones don't. . .

[MattStoke]

11 minutes ago, Met4Cast said:

Correct. The idea that you can have deeper troughs in a more energised jet stream but not more amplified highs is bizarre, that would go against the laws of physics unfortunately. For every action there is an equal and opposite reaction. Deeper troughs mean that somewhere an amplified high must also exist. That's just basic meteorology 101.

+AAM which is often the result of +FT or +MT events essentially take energy from the rotation of the earth and transfers it into the atmosphere which leads to stronger westerlies within the overall wind budget, this in turn leads to a more disturbed jet stream (due to the injected energy). These disturbances then travel across the planet in an easterly direction leading to deeper troughs and more amplified highs. 

What you're saying is absolutely right. A strong jet stream in the Atlantic, it's true, often leads to flat zonal patterns, however I think people are confusing localised phenomena with the hemisphere. I'm talking about the energy in the overall system. 

A feature of El Nino is stronger westerly trade winds in the Pacific. There's a reason blocking is more likely during El Nino years and that reason is added westerly energy into the overall windflow budget.

I mean, all of that is correct but it's not the same as a stronger jet stream being more amplified and occurring more in summer, or vice versa.

[Met4Cast]

1 minute ago, MattStoke said:

I mean, all of that is correct but it's not the same as a stronger jet stream being more amplified and occurring more in summer, or vice versa.

I think you might want to go back and read my initial post again, I didn't say "stronger jet" I said "more energised", i.e more energy in the overall windflow budget which does lead to a more amplified jet stream.

Edited October 26, 2023 by Met4Cast

[Metwatch]

Think we need @MattH and also @Tamara to give us a better insight into the physics of the mid latitude polar jetstream and its associated impacts

Edited October 26, 2023 by Metwatch

[MattStoke]

7 minutes ago, Met4Cast said:

I think you might want to go back and read my initial post again, I didn't say "stronger jet" I said "more energised".

More energized = stronger. 

Maybe it's just a misunderstanding of semantics. To me, more energy = stronger. 

Still makes completely wrong the claim that a more amplified jet stream occurs in winter. The jet stream is more energised by greater thermal gradients, which occur more in winter, leading to more zonality.

Edited October 26, 2023 by MattStoke

[Met4Cast]

2 minutes ago, MattStoke said:

More energized = stronger. 

Maybe it's just a misunderstanding of semantics. To me, more energy = stronger. 

Still makes completely wrong the claim that a more amplified jet stream occurs in winter. The jet stream is more energised by greater thermal gradients, which occur more in winter.

But.. it does.. the jet stream is more amplified in winter, or at least has the ability to be.

The jet stream doesn't dig nearly as far N>S in summer compared to winter.. you've somewhat contradicted yourself there. Maybe we're disagreeing on what we mean by "amplified".  To me, i'm talking about how big the "waves" are, i.e between troughs and peaks, in winter, those are far greater, in summer they are smaller. 

Edited October 26, 2023 by Met4Cast

[MattStoke]

9 minutes ago, Met4Cast said:

But.. it does.. the jet stream is more amplified in winter, or at least has the ability to be.

The jet stream doesn't dig nearly as far N>S in summer compared to winter.. you've somewhat contradicted yourself there. Maybe we're disagreeing on what we mean by "amplified".  To me, i'm talking about how big the "waves" are, i.e between troughs and peaks, in winter, those are far greater, in summer they are smaller. 

So the size and depth of ridges and troughs, then. Not the frequency and regularity of alternating ridges and troughs, with greater incidences of both seen in winter and what is normally what people refer to when saying the jet stream is more amplified when weaker.

That makes more sense.

[damianslaw]

1 hour ago, MattStoke said:

A more energized jet stream is less amplified, not more. It's a weaker jet stream that allows mid to high latitude blocking high pressure to set up.

All depends on where the jet aligns. You can have an energised more southerly tracking jet as current and for the foreseeable. 

[damianslaw]

1 hour ago, Met4Cast said:

I'm sorry but I'm 99% you are incorrect on this. 

Think of the ocean, large waves require more energy in the system not less, big waves have far higher peaks and far deeper troughs compared to a calm ocean, the same principle applies to the jet stream. To get a highly amplified jet stream (and thus, areas of blocking & troughs) you need energy injected into it, it's the exact reason why you see a far more amplified jet stream in the winter compared to the summer. 

The jet has more energy in winter due to the thermal temperature difference and thus is able to be more amplified compared to the weaker energy during the summer.

The more energised the jet, the deeper the lows and conversely stronger the ridges/highs, as the strength of the jet is aligned to thermal temp differentials which are greater in winter, resulting in much lower pressure, and sudden cyclogenesis. 

The atlantic SST profile is a factor in this regard, the anomalous warmth whilst conducive to more intense rain, might be a factor in sending the jet more south, given the temp differentials between north and south atlantic are much lower than if the north atlantic was colder than normal and mid atlantic warmer... I might be completely wrong in my logic.

Edited October 26, 2023 by damianslaw

[MattStoke]

The wonders of the English language causing untold confusion! Especially to my Aspie brain.

[sebastiaan1973]

Quite impressive https://charts.ecmwf.int/products/extended-anomaly-10t?base_time=202310260000&projection=opencharts_arctic&valid_time=202312110000

[bluearmy]

57 minutes ago, sebastiaan1973 said:

Quite impressive https://charts.ecmwf.int/products/extended-anomaly-10t?base_time=202310260000&projection=opencharts_arctic&valid_time=202312110000

Yes considering it’s  six weeks out and it’s the follow on from the warming anomoly that’s been showing consistently for the week before - interesting to say the least 

Edited October 26, 2023 by bluearmy

[Uncertainty]

There are 3 solid weeks of Ural blocking preceding that rather remarkable ec 46 stratospheric temp anomaly. If the former manifests the latter could too. Easy to see then how the long time seasonal model prediction of blocking this winter could actually occur. We look east / ne with baited breath…

What a chart btw! Anomaly shows how unusual it is to have a warming forecast in early dec…

[northwestsnow]

That looks a big 'un ..

I'll take the pain and rain if we get a SSW early December ..