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Old January 12th 19, 04:14 AM posted to uk.sci.weather
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Default What causes (Sudden) Stratospheric Warming (SSW)?

Clearly major SSW events can, but not necessarily always, lead to significant cold spells in the U.K. While these warnings seem closely associated with an increased probability of more strongly blocked upper tropospheric flow, the orientation of key components in the flow pattern is crucial for impacts on U.K. weather. We have had repeatly long lived blocking highs close to and SW of the UK since before Christmas 2018, long before the recent major warming. So it would interesting to know if there is any increase in probability of significant winter cold in the U.K when a major warming happens and the upper pattern is already blocked, as opposed to occasions when the flow has been predominantly zonal.

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Old January 12th 19, 08:28 AM posted to uk.sci.weather
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Default What causes (Sudden) Stratospheric Warming (SSW)?

On 11/01/2019 21:25, wrote:



A BBC met bod vague wittering about SSW yesterday evening. GFS has no
trace of any NH SSW out to 15 days. So is the significance a week or 2
after a SSW, , so a "consequence" of the 06 Jan 2019 one?


I've read that it takes typically 2-3 weeks for the effects of a SSW to
make themselves felt down in the troposphere. So yes.
--
John Hall
"Hegel was right when he said that we learn from history
that man can never learn anything from history."
George Bernard Shaw (1856-1950)

Being a bit cynical, I cant' help noticing that every cold spell we get seems to be down to SSW. If it occurs at the same time or just after, then it's the cause. If it occurs 3 weeks after, it's still the cause due to the reason you describe.

I appreciate it takes time to work down to the troposphere, but it is rapidly become the explanation for all our cold spells (makes a change from SST anomalies or El Nino I suppose) without (seemingly) anyone doing a decent job of explaining a the formation SSW event. What explanations there are being at a very general level, as this thread demonstrates. Similar to geography 'O' level (ox-bow lakes are caused by a river meandering) without any explanation of why rivers meander.

Wait for the next fashionable explanation.

Graham
Penzance


You can't expect one weather type at the surface to follow exactly n days/weeks after another event at a different level in the atmosphere Graham. You know there are many other variables and feedbacks in the mix.

Precisely, that was my point really. People dash out to forecast snow, ice & beasts from the east, on the basis of a process they don't fully understand, which may or may not result in a cold spell anything from a day or 2 to a few weeks hence. If it occurs (which given the vagueness involved is a distinct possibility through chance alone) they all shout "we saw it coming", which is all a bit Daily Express!

Graham
Penzance Sunniest day of the year down here.


Oh I have said this so many times. However some *want* snow and will leap on anyone who says they *may* not get it.

I have the scars! It is especially true of SSWs. Some want to believe it will produce snow and cold, but the data do not back this up. It's a 'might'. Even if cold and snow follows a SSW, we still can't be sure about causation, though sometimes the link appears to be clearer than at other times.

-------------------------------------------------------------------------
If the Met Office says it is going to happen. It is going to happen.
;-)
https://www.metoffice.gov.uk/news/re...weather-coming

Len
Wembury
--------------------------------------------------------------------------


They seem to be stretching out the prescience to 6 to 8 weeks after an
event. Just as I was getting used to the idea of 2 to 3 weeks after the
06 Jan 2019 SSW. If you're allowed to move the goal posts then all is
possible.

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Old January 12th 19, 09:17 AM posted to uk.sci.weather
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Default What causes (Sudden) Stratospheric Warming (SSW)?

On Saturday, 12 January 2019 09:28:30 UTC, N_Cook wrote:
On 11/01/2019 21:25, wrote:



A BBC met bod vague wittering about SSW yesterday evening. GFS has no
trace of any NH SSW out to 15 days. So is the significance a week or 2
after a SSW, , so a "consequence" of the 06 Jan 2019 one?


I've read that it takes typically 2-3 weeks for the effects of a SSW to
make themselves felt down in the troposphere. So yes.
--
John Hall
"Hegel was right when he said that we learn from history
that man can never learn anything from history."
George Bernard Shaw (1856-1950)

Being a bit cynical, I cant' help noticing that every cold spell we get seems to be down to SSW. If it occurs at the same time or just after, then it's the cause. If it occurs 3 weeks after, it's still the cause due to the reason you describe.

I appreciate it takes time to work down to the troposphere, but it is rapidly become the explanation for all our cold spells (makes a change from SST anomalies or El Nino I suppose) without (seemingly) anyone doing a decent job of explaining a the formation SSW event. What explanations there are being at a very general level, as this thread demonstrates. Similar to geography 'O' level (ox-bow lakes are caused by a river meandering) without any explanation of why rivers meander.

Wait for the next fashionable explanation.

Graham
Penzance


You can't expect one weather type at the surface to follow exactly n days/weeks after another event at a different level in the atmosphere Graham. You know there are many other variables and feedbacks in the mix.

Precisely, that was my point really. People dash out to forecast snow, ice & beasts from the east, on the basis of a process they don't fully understand, which may or may not result in a cold spell anything from a day or 2 to a few weeks hence. If it occurs (which given the vagueness involved is a distinct possibility through chance alone) they all shout "we saw it coming", which is all a bit Daily Express!

Graham
Penzance Sunniest day of the year down here.

Oh I have said this so many times. However some *want* snow and will leap on anyone who says they *may* not get it.

I have the scars! It is especially true of SSWs. Some want to believe it will produce snow and cold, but the data do not back this up. It's a 'might'. Even if cold and snow follows a SSW, we still can't be sure about causation, though sometimes the link appears to be clearer than at other times..

-------------------------------------------------------------------------
If the Met Office says it is going to happen. It is going to happen.
;-)
https://www.metoffice.gov.uk/news/re...weather-coming

Len
Wembury
--------------------------------------------------------------------------


They seem to be stretching out the prescience to 6 to 8 weeks after an
event. Just as I was getting used to the idea of 2 to 3 weeks after the
06 Jan 2019 SSW. If you're allowed to move the goal posts then all is
possible.

The two to three week timetable is referring to the effects of the SSW being felt in the troposphere - not the arrival of cold weather in the UK. Cold weather in the UK requires any resulting block to form in an appropriate position - you could yet end up with a block that is not in the correct configuration for much cold weather. Latest modelling of flow and temperature (at 10 hPa) in the stratosphere suggest that the warming and flow reversal will persist until late January. The same modelling in the troposphere suggests that a cold spell is likely either in the last week of January or the first week of February. A note of caution, though - some model runs are suggesting mobility, so a cold spell is not clear cut.

Incidentally, the SSW started around 22nd/23rd December - not 6th January - as measured at 10hPa.

--
Freddie
Ystrad
Rhondda
148m AMSL
http://www.hosiene.co.uk/weather/
https://twitter.com/YstradRhonddaWx for hourly reports (very few tweets getting through currently)
Stats for the month so far: https://www.hosiene.co.uk/weather/st...201901JAN.xlsx
  #34   Report Post  
Old January 15th 19, 09:49 AM posted to uk.sci.weather
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Default What causes (Sudden) Stratospheric Warming (SSW)?

GFS has gone right off giving SE England laying snow, out to the end of
January as the earliest.

  #35   Report Post  
Old January 15th 19, 09:53 AM posted to uk.sci.weather
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Default What causes (Sudden) Stratospheric Warming (SSW)?

In message , N_Cook
writes
GFS has gone right off giving SE England laying snow, out to the end of
January as the earliest.


Its operational run has been all over the place in recent days. The GFS
and ECM 0Z operational runs could hardly be more different this morning.
--
John Hall
"Hegel was right when he said that we learn from history
that man can never learn anything from history."
George Bernard Shaw (1856-1950)


  #36   Report Post  
Old January 15th 19, 10:46 AM posted to uk.sci.weather
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Default What causes (Sudden) Stratospheric Warming (SSW)?

On Friday, January 11, 2019 at 9:25:04 PM UTC, wrote:
A BBC met bod vague wittering about SSW yesterday evening. GFS has no
trace of any NH SSW out to 15 days. So is the significance a week or 2
after a SSW, , so a "consequence" of the 06 Jan 2019 one?


I've read that it takes typically 2-3 weeks for the effects of a SSW to
make themselves felt down in the troposphere. So yes.
--
John Hall
"Hegel was right when he said that we learn from history
that man can never learn anything from history."
George Bernard Shaw (1856-1950)

Being a bit cynical, I cant' help noticing that every cold spell we get seems to be down to SSW. If it occurs at the same time or just after, then it's the cause. If it occurs 3 weeks after, it's still the cause due to the reason you describe.

I appreciate it takes time to work down to the troposphere, but it is rapidly become the explanation for all our cold spells (makes a change from SST anomalies or El Nino I suppose) without (seemingly) anyone doing a decent job of explaining a the formation SSW event. What explanations there are being at a very general level, as this thread demonstrates. Similar to geography 'O' level (ox-bow lakes are caused by a river meandering) without any explanation of why rivers meander.

Wait for the next fashionable explanation.

Graham
Penzance


You can't expect one weather type at the surface to follow exactly n days/weeks after another event at a different level in the atmosphere Graham. You know there are many other variables and feedbacks in the mix.

Precisely, that was my point really. People dash out to forecast snow, ice & beasts from the east, on the basis of a process they don't fully understand, which may or may not result in a cold spell anything from a day or 2 to a few weeks hence. If it occurs (which given the vagueness involved is a distinct possibility through chance alone) they all shout "we saw it coming", which is all a bit Daily Express!

Graham
Penzance Sunniest day of the year down here.


Oh I have said this so many times. However some *want* snow and will leap on anyone who says they *may* not get it.

I have the scars! It is especially true of SSWs. Some want to believe it will produce snow and cold, but the data do not back this up. It's a 'might'. Even if cold and snow follows a SSW, we still can't be sure about causation, though sometimes the link appears to be clearer than at other times.

-------------------------------------------------------------------------
If the Met Office says it is going to happen. It is going to happen.
;-)
https://www.metoffice.gov.uk/news/re...weather-coming

Len
Wembury
--------------------------------------------------------------------------


I know you're tongue in cheek Len.

In December the Meto were predicting cold before now. On the Meto own website, dated 20th December

Jeff Knight, Manager of Modelling Climate Variability at the Met Office says “There is now a very high likelihood of an SSW happening around the end of the year. This increases the chances of colder-than-average weather in January and the rest of winter.”

Well, 1 month on, still waiting, it's been relentless mild here. When there eventually is a proper cold spell, I'm sure the wonders of SSW forecasting will be worshipped. If there isn't it will be quietly forgotten. As John says elsewhere in this thread, even the models are struggling what to make of it all, NW winds . . toppling ridge . . easterly . . brief northerly . . pressure staying locked to the SW . . Each day brings a new view.

Me, I think it's interesting, certainly fashionable, but as a useful forecasting tool for the general public, pretty meaningless. Of course, for the Daily Express it's manna from heaven. Forecasting 5 days ahead often turns out little better than inspired guesswork.

Graham
Penzance
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Old January 15th 19, 11:51 AM posted to uk.sci.weather
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Default What causes (Sudden) Stratospheric Warming (SSW)?

On Tuesday, 15 January 2019 11:46:38 UTC, Graham Easterling wrote:
On Friday, January 11, 2019 at 9:25:04 PM UTC, wrote:
A BBC met bod vague wittering about SSW yesterday evening. GFS has no
trace of any NH SSW out to 15 days. So is the significance a week or 2
after a SSW, , so a "consequence" of the 06 Jan 2019 one?


I've read that it takes typically 2-3 weeks for the effects of a SSW to
make themselves felt down in the troposphere. So yes.
--
John Hall
"Hegel was right when he said that we learn from history
that man can never learn anything from history."
George Bernard Shaw (1856-1950)

Being a bit cynical, I cant' help noticing that every cold spell we get seems to be down to SSW. If it occurs at the same time or just after, then it's the cause. If it occurs 3 weeks after, it's still the cause due to the reason you describe.

I appreciate it takes time to work down to the troposphere, but it is rapidly become the explanation for all our cold spells (makes a change from SST anomalies or El Nino I suppose) without (seemingly) anyone doing a decent job of explaining a the formation SSW event. What explanations there are being at a very general level, as this thread demonstrates. Similar to geography 'O' level (ox-bow lakes are caused by a river meandering) without any explanation of why rivers meander.

Wait for the next fashionable explanation.

Graham
Penzance


You can't expect one weather type at the surface to follow exactly n days/weeks after another event at a different level in the atmosphere Graham. You know there are many other variables and feedbacks in the mix.

Precisely, that was my point really. People dash out to forecast snow, ice & beasts from the east, on the basis of a process they don't fully understand, which may or may not result in a cold spell anything from a day or 2 to a few weeks hence. If it occurs (which given the vagueness involved is a distinct possibility through chance alone) they all shout "we saw it coming", which is all a bit Daily Express!

Graham
Penzance Sunniest day of the year down here.

Oh I have said this so many times. However some *want* snow and will leap on anyone who says they *may* not get it.

I have the scars! It is especially true of SSWs. Some want to believe it will produce snow and cold, but the data do not back this up. It's a 'might'. Even if cold and snow follows a SSW, we still can't be sure about causation, though sometimes the link appears to be clearer than at other times.

-------------------------------------------------------------------------
If the Met Office says it is going to happen. It is going to happen.
;-)
https://www.metoffice.gov.uk/news/re...weather-coming

Len
Wembury
--------------------------------------------------------------------------


I know you're tongue in cheek Len.

In December the Meto were predicting cold before now. On the Meto own website, dated 20th December

Jeff Knight, Manager of Modelling Climate Variability at the Met Office says “There is now a very high likelihood of an SSW happening around the end of the year. This increases the chances of colder-than-average weather in January and the rest of winter.”

Well, 1 month on, still waiting, it's been relentless mild here. When there eventually is a proper cold spell, I'm sure the wonders of SSW forecasting will be worshipped. If there isn't it will be quietly forgotten. As John says elsewhere in this thread, even the models are struggling what to make of it all, NW winds . . toppling ridge . . easterly . . brief northerly . .. pressure staying locked to the SW . . Each day brings a new view.

Me, I think it's interesting, certainly fashionable, but as a useful forecasting tool for the general public, pretty meaningless. Of course, for the Daily Express it's manna from heaven. Forecasting 5 days ahead often turns out little better than inspired guesswork.

An SSW event can lead to disruption of the tropospheric flow. That's what is known about SSWs. What isn't known is the location and orientation of any subsequent blocking systems that may occur - the genesis of which will be down to precisely how the disruption of the tropospheric flow occurs. The disruption takes two or three weeks to occur. We have had a block affecting the UK since Christmas (you mentioned your non-variable weather in another post). The block is now retrogressing, with a northwesterly jet affecting the UK. The timescale for this change is coincident with the anticipated effect of the SSW. I'm not saying it is the SSW that is responsible for the retrogression - but the timing is pretty coincidental. No doubt somebody with the resources will analyse what happened in due course.

The MO spokesperson didn't say that we would have a cold spell by now - he said it "increases the chances of colder-than-average weather..." which isn't the same thing. We should reserve judgement until after the event - especially as the disruption to the tropospheric flow is only just starting. It is going to be interesting to watch how things evolve. The different model solutions show that minor differences in the starting conditions will have a massive effect in the outcome. Hopefully in the next few days we may see more agreement in the medium range.

My money is on it being unsettled with the jet displaced to the south of the UK, bringing lows on more southerly tracks, with wild swings in temperature, but any mild spells brief - with the potential for severe weather on transition to/from cold air. I think on balance the cold air will affect us a fair bit more than the mild, leading to a spell of below-average temperatures and above-average precipitation. Although Scotland may be drier than average if the jetstream is far enough south

We shall see, come Valentine's day :-)

--
Freddie
Ystrad
Rhondda
148m AMSL
http://www.hosiene.co.uk/weather/
https://twitter.com/YstradRhonddaWx for hourly reports (very few tweets getting through currently)
Stats for the month so far: https://www.hosiene.co.uk/weather/st...201901JAN.xlsx
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Old January 15th 19, 12:29 PM posted to uk.sci.weather
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Default What causes (Sudden) Stratospheric Warming (SSW)?

On Tuesday, January 15, 2019 at 11:46:38 AM UTC, Graham Easterling wrote:
On Friday, January 11, 2019 at 9:25:04 PM UTC, wrote:
A BBC met bod vague wittering about SSW yesterday evening. GFS has no
trace of any NH SSW out to 15 days. So is the significance a week or 2
after a SSW, , so a "consequence" of the 06 Jan 2019 one?


I've read that it takes typically 2-3 weeks for the effects of a SSW to
make themselves felt down in the troposphere. So yes.
--
John Hall
"Hegel was right when he said that we learn from history
that man can never learn anything from history."
George Bernard Shaw (1856-1950)

Being a bit cynical, I cant' help noticing that every cold spell we get seems to be down to SSW. If it occurs at the same time or just after, then it's the cause. If it occurs 3 weeks after, it's still the cause due to the reason you describe.

I appreciate it takes time to work down to the troposphere, but it is rapidly become the explanation for all our cold spells (makes a change from SST anomalies or El Nino I suppose) without (seemingly) anyone doing a decent job of explaining a the formation SSW event. What explanations there are being at a very general level, as this thread demonstrates. Similar to geography 'O' level (ox-bow lakes are caused by a river meandering) without any explanation of why rivers meander.

Wait for the next fashionable explanation.

Graham
Penzance


You can't expect one weather type at the surface to follow exactly n days/weeks after another event at a different level in the atmosphere Graham. You know there are many other variables and feedbacks in the mix.

Precisely, that was my point really. People dash out to forecast snow, ice & beasts from the east, on the basis of a process they don't fully understand, which may or may not result in a cold spell anything from a day or 2 to a few weeks hence. If it occurs (which given the vagueness involved is a distinct possibility through chance alone) they all shout "we saw it coming", which is all a bit Daily Express!

Graham
Penzance Sunniest day of the year down here.

Oh I have said this so many times. However some *want* snow and will leap on anyone who says they *may* not get it.

I have the scars! It is especially true of SSWs. Some want to believe it will produce snow and cold, but the data do not back this up. It's a 'might'. Even if cold and snow follows a SSW, we still can't be sure about causation, though sometimes the link appears to be clearer than at other times.

-------------------------------------------------------------------------
If the Met Office says it is going to happen. It is going to happen.
;-)
https://www.metoffice.gov.uk/news/re...weather-coming

Len
Wembury
--------------------------------------------------------------------------


I know you're tongue in cheek Len.

In December the Meto were predicting cold before now. On the Meto own website, dated 20th December

Jeff Knight, Manager of Modelling Climate Variability at the Met Office says “There is now a very high likelihood of an SSW happening around the end of the year. This increases the chances of colder-than-average weather in January and the rest of winter.”

Well, 1 month on, still waiting, it's been relentless mild here. When there eventually is a proper cold spell, I'm sure the wonders of SSW forecasting will be worshipped. If there isn't it will be quietly forgotten. As John says elsewhere in this thread, even the models are struggling what to make of it all, NW winds . . toppling ridge . . easterly . . brief northerly . .. pressure staying locked to the SW . . Each day brings a new view.

Me, I think it's interesting, certainly fashionable, but as a useful forecasting tool for the general public, pretty meaningless. Of course, for the Daily Express it's manna from heaven. Forecasting 5 days ahead often turns out little better than inspired guesswork.

Graham
Penzance

--------------------------------------------------------------------------
O ye of little faith, Graham.
Just wait until next week.

No seriously, the effect of a SSW event at a particular location has always been uncertain.
It seems the Alps have copped it this time.
At no time has another 'beast from the east' been forecast.

Blocked it has been.
Shades of grey I would say.
Models don't cope with it that well.

Len
Wembury

--------------------------------------------------------------------------------



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Old January 15th 19, 12:37 PM posted to uk.sci.weather
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Default What causes (Sudden) Stratospheric Warming (SSW)?

On Tuesday, January 15, 2019 at 12:51:43 PM UTC, Freddie wrote:
On Tuesday, 15 January 2019 11:46:38 UTC, Graham Easterling wrote:
On Friday, January 11, 2019 at 9:25:04 PM UTC, wrote:
A BBC met bod vague wittering about SSW yesterday evening. GFS has no
trace of any NH SSW out to 15 days. So is the significance a week or 2
after a SSW, , so a "consequence" of the 06 Jan 2019 one?


I've read that it takes typically 2-3 weeks for the effects of a SSW to
make themselves felt down in the troposphere. So yes.
--
John Hall
"Hegel was right when he said that we learn from history
that man can never learn anything from history."
George Bernard Shaw (1856-1950)

Being a bit cynical, I cant' help noticing that every cold spell we get seems to be down to SSW. If it occurs at the same time or just after, then it's the cause. If it occurs 3 weeks after, it's still the cause due to the reason you describe.

I appreciate it takes time to work down to the troposphere, but it is rapidly become the explanation for all our cold spells (makes a change from SST anomalies or El Nino I suppose) without (seemingly) anyone doing a decent job of explaining a the formation SSW event. What explanations there are being at a very general level, as this thread demonstrates. Similar to geography 'O' level (ox-bow lakes are caused by a river meandering) without any explanation of why rivers meander.

Wait for the next fashionable explanation.

Graham
Penzance


You can't expect one weather type at the surface to follow exactly n days/weeks after another event at a different level in the atmosphere Graham. You know there are many other variables and feedbacks in the mix..

Precisely, that was my point really. People dash out to forecast snow, ice & beasts from the east, on the basis of a process they don't fully understand, which may or may not result in a cold spell anything from a day or 2 to a few weeks hence. If it occurs (which given the vagueness involved is a distinct possibility through chance alone) they all shout "we saw it coming", which is all a bit Daily Express!

Graham
Penzance Sunniest day of the year down here.

Oh I have said this so many times. However some *want* snow and will leap on anyone who says they *may* not get it.

I have the scars! It is especially true of SSWs. Some want to believe it will produce snow and cold, but the data do not back this up. It's a 'might'. Even if cold and snow follows a SSW, we still can't be sure about causation, though sometimes the link appears to be clearer than at other times.
-------------------------------------------------------------------------
If the Met Office says it is going to happen. It is going to happen.
;-)
https://www.metoffice.gov.uk/news/re...weather-coming

Len
Wembury
--------------------------------------------------------------------------


I know you're tongue in cheek Len.

In December the Meto were predicting cold before now. On the Meto own website, dated 20th December

Jeff Knight, Manager of Modelling Climate Variability at the Met Office says “There is now a very high likelihood of an SSW happening around the end of the year. This increases the chances of colder-than-average weather in January and the rest of winter.”

Well, 1 month on, still waiting, it's been relentless mild here. When there eventually is a proper cold spell, I'm sure the wonders of SSW forecasting will be worshipped. If there isn't it will be quietly forgotten. As John says elsewhere in this thread, even the models are struggling what to make of it all, NW winds . . toppling ridge . . easterly . . brief northerly .. . pressure staying locked to the SW . . Each day brings a new view.

Me, I think it's interesting, certainly fashionable, but as a useful forecasting tool for the general public, pretty meaningless. Of course, for the Daily Express it's manna from heaven. Forecasting 5 days ahead often turns out little better than inspired guesswork.

An SSW event can lead to disruption of the tropospheric flow. That's what is known about SSWs. What isn't known is the location and orientation of any subsequent blocking systems that may occur - the genesis of which will be down to precisely how the disruption of the tropospheric flow occurs. The disruption takes two or three weeks to occur. We have had a block affecting the UK since Christmas (you mentioned your non-variable weather in another post). The block is now retrogressing, with a northwesterly jet affecting the UK. The timescale for this change is coincident with the anticipated effect of the SSW. I'm not saying it is the SSW that is responsible for the retrogression - but the timing is pretty coincidental. No doubt somebody with the resources will analyse what happened in due course.

The MO spokesperson didn't say that we would have a cold spell by now - he said it "increases the chances of colder-than-average weather..." which isn't the same thing. We should reserve judgement until after the event - especially as the disruption to the tropospheric flow is only just starting. It is going to be interesting to watch how things evolve. The different model solutions show that minor differences in the starting conditions will have a massive effect in the outcome. Hopefully in the next few days we may see more agreement in the medium range.

My money is on it being unsettled with the jet displaced to the south of the UK, bringing lows on more southerly tracks, with wild swings in temperature, but any mild spells brief - with the potential for severe weather on transition to/from cold air. I think on balance the cold air will affect us a fair bit more than the mild, leading to a spell of below-average temperatures and above-average precipitation. Although Scotland may be drier than average if the jetstream is far enough south

We shall see, come Valentine's day :-)

--
Freddie
Ystrad
Rhondda
148m AMSL
http://www.hosiene.co.uk/weather/
https://twitter.com/YstradRhonddaWx for hourly reports (very few tweets getting through currently)
Stats for the month so far: https://www.hosiene.co.uk/weather/st...201901JAN.xlsx


Thanks for all that.

I'm certainly not saying a SSW event does not affect our weather, I'm sure it must. The trouble is that the detail of how it will evolve is currently fairly unpredictable, both in exactly when, how & by what degree.

Saying 'it might' do something is fair enough. The trouble is it's being jumped on rather, and not only by the press, a lot of weather presenters have been hyping it up rather.

Earlier in this thread I said

"Ahead of a warm front the visibility commonly becomes very good, high cloud streams in etc. It is therefore possible to forecast the likelyhood of rain followed by mizzle (certainly in Cornwall). The sequence is known without any need for an understanding of the mechanisms involved."
and
"What explanations there are being at a very general level, as this thread demonstrates. Similar to geography 'O' level (ox-bow lakes are caused by a river meandering) without any explanation of why rivers meander."

In the case of why rivers meander there is a lot of detail available - something I studied at degree level. Run water down a pane of glass, it will still meander.

In the context of SSW, it is known it can result in a cold spell by propagating downwards, but what instigates SSW? If that's better understood perhaps it will become a better tool for prediction.

Graham
Penzance
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Old January 15th 19, 01:09 PM posted to uk.sci.weather
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Default What causes (Sudden) Stratospheric Warming (SSW)?

On Tuesday, 15 January 2019 13:37:56 UTC, Graham Easterling wrote:
On Tuesday, January 15, 2019 at 12:51:43 PM UTC, Freddie wrote:
On Tuesday, 15 January 2019 11:46:38 UTC, Graham Easterling wrote:
On Friday, January 11, 2019 at 9:25:04 PM UTC, wrote:
A BBC met bod vague wittering about SSW yesterday evening. GFS has no
trace of any NH SSW out to 15 days. So is the significance a week or 2
after a SSW, , so a "consequence" of the 06 Jan 2019 one?


I've read that it takes typically 2-3 weeks for the effects of a SSW to
make themselves felt down in the troposphere. So yes.
--
John Hall
"Hegel was right when he said that we learn from history
that man can never learn anything from history."
George Bernard Shaw (1856-1950)

Being a bit cynical, I cant' help noticing that every cold spell we get seems to be down to SSW. If it occurs at the same time or just after, then it's the cause. If it occurs 3 weeks after, it's still the cause due to the reason you describe.

I appreciate it takes time to work down to the troposphere, but it is rapidly become the explanation for all our cold spells (makes a change from SST anomalies or El Nino I suppose) without (seemingly) anyone doing a decent job of explaining a the formation SSW event. What explanations there are being at a very general level, as this thread demonstrates. Similar to geography 'O' level (ox-bow lakes are caused by a river meandering) without any explanation of why rivers meander.

Wait for the next fashionable explanation.

Graham
Penzance


You can't expect one weather type at the surface to follow exactly n days/weeks after another event at a different level in the atmosphere Graham. You know there are many other variables and feedbacks in the mix.

Precisely, that was my point really. People dash out to forecast snow, ice & beasts from the east, on the basis of a process they don't fully understand, which may or may not result in a cold spell anything from a day or 2 to a few weeks hence. If it occurs (which given the vagueness involved is a distinct possibility through chance alone) they all shout "we saw it coming", which is all a bit Daily Express!

Graham
Penzance Sunniest day of the year down here.

Oh I have said this so many times. However some *want* snow and will leap on anyone who says they *may* not get it.

I have the scars! It is especially true of SSWs. Some want to believe it will produce snow and cold, but the data do not back this up. It's a 'might'. Even if cold and snow follows a SSW, we still can't be sure about causation, though sometimes the link appears to be clearer than at other times.
-------------------------------------------------------------------------
If the Met Office says it is going to happen. It is going to happen..
;-)
https://www.metoffice.gov.uk/news/re...weather-coming

Len
Wembury
--------------------------------------------------------------------------

I know you're tongue in cheek Len.

In December the Meto were predicting cold before now. On the Meto own website, dated 20th December

Jeff Knight, Manager of Modelling Climate Variability at the Met Office says “There is now a very high likelihood of an SSW happening around the end of the year. This increases the chances of colder-than-average weather in January and the rest of winter.”

Well, 1 month on, still waiting, it's been relentless mild here. When there eventually is a proper cold spell, I'm sure the wonders of SSW forecasting will be worshipped. If there isn't it will be quietly forgotten. As John says elsewhere in this thread, even the models are struggling what to make of it all, NW winds . . toppling ridge . . easterly . . brief northerly . . pressure staying locked to the SW . . Each day brings a new view.

Me, I think it's interesting, certainly fashionable, but as a useful forecasting tool for the general public, pretty meaningless. Of course, for the Daily Express it's manna from heaven. Forecasting 5 days ahead often turns out little better than inspired guesswork.

An SSW event can lead to disruption of the tropospheric flow. That's what is known about SSWs. What isn't known is the location and orientation of any subsequent blocking systems that may occur - the genesis of which will be down to precisely how the disruption of the tropospheric flow occurs. The disruption takes two or three weeks to occur. We have had a block affecting the UK since Christmas (you mentioned your non-variable weather in another post). The block is now retrogressing, with a northwesterly jet affecting the UK. The timescale for this change is coincident with the anticipated effect of the SSW. I'm not saying it is the SSW that is responsible for the retrogression - but the timing is pretty coincidental. No doubt somebody with the resources will analyse what happened in due course.

The MO spokesperson didn't say that we would have a cold spell by now - he said it "increases the chances of colder-than-average weather..." which isn't the same thing. We should reserve judgement until after the event - especially as the disruption to the tropospheric flow is only just starting. It is going to be interesting to watch how things evolve. The different model solutions show that minor differences in the starting conditions will have a massive effect in the outcome. Hopefully in the next few days we may see more agreement in the medium range.

My money is on it being unsettled with the jet displaced to the south of the UK, bringing lows on more southerly tracks, with wild swings in temperature, but any mild spells brief - with the potential for severe weather on transition to/from cold air. I think on balance the cold air will affect us a fair bit more than the mild, leading to a spell of below-average temperatures and above-average precipitation. Although Scotland may be drier than average if the jetstream is far enough south

We shall see, come Valentine's day :-)

--
Freddie
Ystrad
Rhondda
148m AMSL
http://www.hosiene.co.uk/weather/
https://twitter.com/YstradRhonddaWx for hourly reports (very few tweets getting through currently)
Stats for the month so far: https://www.hosiene.co.uk/weather/st...201901JAN.xlsx


Thanks for all that.

I'm certainly not saying a SSW event does not affect our weather, I'm sure it must. The trouble is that the detail of how it will evolve is currently fairly unpredictable, both in exactly when, how & by what degree.

Saying 'it might' do something is fair enough. The trouble is it's being jumped on rather, and not only by the press, a lot of weather presenters have been hyping it up rather.

Earlier in this thread I said

"Ahead of a warm front the visibility commonly becomes very good, high cloud streams in etc. It is therefore possible to forecast the likelyhood of rain followed by mizzle (certainly in Cornwall). The sequence is known without any need for an understanding of the mechanisms involved."
and
"What explanations there are being at a very general level, as this thread demonstrates. Similar to geography 'O' level (ox-bow lakes are caused by a river meandering) without any explanation of why rivers meander."

In the case of why rivers meander there is a lot of detail available - something I studied at degree level. Run water down a pane of glass, it will still meander.

In the context of SSW, it is known it can result in a cold spell by propagating downwards, but what instigates SSW? If that's better understood perhaps it will become a better tool for prediction.

River meanders and SSW events are pretty closely related, believe it or not! Research indicates that a SSW event is instigated by Rossby waves in the troposphere. Rossby waves are meanders in the jet stream. There is some useful background on Wikipedia: https://en.wikipedia.org/wiki/Rossby_wave. As it says here, SSW events are triggered by poleward-moving Rossby waves. It's a pretty well-understood subject. That's why the models can forecast them.

There needs to be a lot of things in place for a SSW event to cause a cold spell - that's why I said that what we know is that they cause disruption to the tropospheric flow. Whether that disruption leads to a cold spell for the UK is another thing.

I agree completely that the media jumping on such phenomena as SSW events is counterproductive, as they raise general expectations with the resulting disappointment/disillusionment leading to the phenomena not being believed.

--
Freddie
Ystrad
Rhondda
148m AMSL
http://www.hosiene.co.uk/weather/
https://twitter.com/YstradRhonddaWx for hourly reports (very few tweets getting through currently)
Stats for the month so far: https://www.hosiene.co.uk/weather/st...201901JAN.xlsx



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