Hunt For Cold: Model Discussion - Heading Into Christmas

[Mike Poole]

GEFS zonal wind chart with reversal today at 10 hPa 60 N.

I'm struck again by the model maintaining the reverse winds right through the run.  ECM also has reverse winds at 10 hPa at t240 still:

Reverse showing also at 30 hPa at that point.

With such an upheaval in the strat, plus the MJO seemingly favourable, we would very unlucky to miss out on a cold spell at some point over the next 6 weeks or so, in my view.

Edited January 1, 2019 by Mike Poole

[Premiere Neige]

26 minutes ago, Purga said:

OK worth remembering:

Not all SSW's produce cold spells in the UK - they increase the chances of blocking and colder weather.
Not all SSW's are the same. This one appears to have been a 'displacement' type event followed by a split.
Stratospheric events do indeed take 2 to 3 weeks to completely impact the troposphere - if indeed they do...not all do.
The current MJO is now expected to propagate into a strong phase 6/7 which would tend to encourage a negative NAO by late January.
We've been in a moderate El Nino - which tends to produce milder first halves to winter in northwest Europe and 'colder' second halves. (This can be masked though by the general ongoing seasonal cooling which makes January/February colder than December anyway). This appears to have trended neutral recently.
We're at the bottom of the decadal solar cycle where colder, more blocked winter tend to cluster.

One slight fly in the ointment is that the QBO has shifted westerly from easterly (which favours blocking i.e. cold) but hopefully it's being damped out by the other strongly favourable signals.

The strongest signal for easterlies from both GLOSEA and ECM has always been Mid January - February.
There are now tentative signs in the NWP of the disruptive effects of the SSW.

So all to play for.

As I understand it there is a lag time for effects to be felt with regard to a switch in the QBO?

[ArHu3]

1 hour ago, northwestsnow said:

Happy NY blue, i was pondering this myself TBH the other day...

Is the MJO going to be the main driver as opposed to the SSW?

Still on target this morning acc to Exeter..

Since ssws seldom deliver cold in western Europe (unless they are splits) that forecast was probably based on a whole lot of other factors too

 

Edit : iirc they also have an algorithm for calculating the likelihood of certain patterns following another pattern 

Edit 2:

https://www.metoffice.gov.uk/research/news/2016/new-weather-patterns-for-uk-and-europe

Edited January 1, 2019 by ArHu3

[Purga]

16 minutes ago, Premier Neige said:

As I understand it there is a lag time for effects to be felt with regard to a switch in the QBO?

There is indeed but this is quite variable maybe 30-40 days and also dependent on the level in the atmosphere and also varies in degree.

SSW's are found rather more likely to occur more during easterly QBO phases. Each phase lasts approx 28 months.

[pdiddy]

7 minutes ago, ArHu3 said:

Since ssws seldom deliver cold in western Europe (unless they are splits) that forecast was probably based on a whole lot of other factors too

Happy to be corrected if you have evidence to support, but not true according to the Met Office:

What impact does this have on the UK?

We normally expect our weather to come in from the west - with a flow of relatively mild air coming in off the Atlantic.

When an SSW brings easterly winds this tends to alter our weather patterns slightly, weakening areas of low pressure and moving our jet stream further south. This leads to high pressure over the North Atlantic, 'blocking' that flow of mild Atlantic air and dragging in cold air from the continent to the east. Exactly how cold it might be depends on the details of where the air comes from.

SSWs don't always result in this outcome - but a cold snap follows more often than not, so the SSW greatly increases the risk of wintry weather.

https://www.metoffice.gov.uk/learning/wind/sudden-stratospheric-warming

 

Edited January 1, 2019 by pdiddy

[Catacol]

58 minutes ago, bluearmy said:

I wonder how much Exeter’s jan cold punt was predicated on the MJO and how much on the SSW ????

That's a really good question. Ying and Yang. Slower progression of the MJO in recent days has added to the frustration on here....but might also add to the size of the honey pot...

ECM good this morning - ties in with the 150hpa strat chart which suggests the Siberian lobe of split vortex may be held back further east allowing at least a temporary surge of scandy heights - greeny still the likely direction of travel?

Notice also a resumption in wave 2 activity on the vortex

Upgrade charts coming inside the horizon. Honey pot visible. Potential longevity of what is coming possibly pleasing ('twas the only negative about the March Beast). 

HNY to all on here!

 

[ArHu3]

23 minutes ago, pdiddy said:

not true according to the Met Office:

What impact does this have on the UK?

We normally expect our weather to come in from the west - with a flow of relatively mild air coming in off the Atlantic.

When an SSW brings easterly winds this tends to alter our weather patterns slightly, weakening areas of low pressure and moving our jet stream further south. This leads to high pressure over the North Atlantic, 'blocking' that flow of mild Atlantic air and dragging in cold air from the continent to the east. Exactly how cold it might be depends on the details of where the air comes from.

SSWs don't always result in this outcome - but a cold snap follows more often than not, so the SSW greatly increases the risk of wintry weather.

https://www.metoffice.gov.uk/learning/wind/sudden-stratospheric-warming

 

 

(I also checked hellmann numbers after ssw, to make sure cold spells weren't alternated with warmer periods but that also wasn't the case) 

Edited January 1, 2019 by ArHu3

[snowfish1]

17 minutes ago, ArHu3 said:

 

 

Do I read the animated chart right that the polar vortex expands in our region of the hemisphere?  A huge mass of. Cold air associated with it? I'm still learning 

Edited January 1, 2019 by snowfish1

[ArHu3]

1 minute ago, snowfish1 said:

Do I read the animated chart right that the polar vortex expands in our region of the hemisphere?  A huge mass of. Cold air associated with it? I'm still learning 

I meant to link to giacomo masoto's reply, not Judah Cohen with a link to a research paper showing that for western Europe displacements generally unfavorable for cold

[MattStoke]

Isn’t it a split we’re seeing though? Not a displacement.

[Eastnorthwest]

Charts starting to hint like said towards what we want but a long time still for them to keep swinging from positive to negativity but I still say we will see real cold till middle of the month which might only be a few days or a couple of weeks we should know by the weekend ,till then as all ways the chart runs will keep changing from run to run beyond T 168 some good some not so good but we've had a couple of corkers already in fantasy land  showing the block we want so all to play for in the coming days

All good hints which we didn't have 2 days ago which is moving in the right direction 

[Methuselah]

For anyone who's still unsure, this is a very informative video:

I put it in here cos it affects the hunt for cold.

[northwestsnow]

27 minutes ago, ArHu3 said:

I meant to link to giacomo masoto's reply, not Judah Cohen with a link to a research paper showing that for western Europe displacements generally unfavorable for cold

According to the bbc posted above,2 out of 3 SSWs result in cold for UK..

Edited January 1, 2019 by northwestsnow

[snowray]

I'm certainly feeling a lot more positive today, signs that the times are a changing as we enter 2019. At the end of the day, I'd be happy with just 2 or 3 days of cold with some snowfall, it's not as if I'm being greedy. 

But none the less a late Jan 1947 repeat is long, long over due. This is how it developed, some similarities there in the 1st two charts to what we have showing now, from nothing to super cold, and the cold and snow continued well into February 1947.

[winterof79]

2 hours ago, feb1991blizzard said:

Either way now, it looks like hopefully my fears about the split not being wide enough or long lasting enough could be over, last good few GFS ops have stonking cross polar ridging in the strat with slow signs of downwelling, and its getting near to the reliable as well.

I am thinking they based it on both

[CanadaAl]

Happy new year everyone.

Cheeky little new years treat from the ECM:

[northwestsnow]

Just now, winterof79 said:

I am thinking they based it on both

Nice find mate

Think i will go along with the pros for now..

[gottolovethisweather]

Not sure what the long-term prospects hold because I haven't been following every update but the short-term appears to have the cold upped a notch. Media forecasts showing Maximum temperatures of 3c or 4c even down south in the big cities, come, the end of the week. Not far removed from my expectations here I think, with a colder scenario slowly developing and snow in the mix by week two or three?

[johnholmes]

5 minutes ago, snowray said:

I'm certainly feeling a lot more positive today, signs that the times are a changing as we enter 2019. At the end of the day, I'd be happy with just 2 or 3 days of cold with some snowfall, it's not as if I'm being greedy. 

But none the less a late Jan 1947 repeat is long, long over due. This is how it developed, some similarities there in the 1st two charts to what we have showing now, from nothing to super cold, and the cold and snow continued well into February 1947.

 

 

 

 

 

Actually for the Midlands and north into March; this is a brilliant site

http://swanstonweather.co.uk/EppingWeatherPages/Index.html

[winterof79]

5 minutes ago, northwestsnow said:

Nice find mate

Think i will go along with the pros for now..

That was on the 12th December so a good call from Glosea and why the MET have been steadfast with mid winter cold

[CanadaAl]

8 minutes ago, gottolovethisweather said:

Not sure what the long-term prospects hold because I haven't been following every update but the short-term appears to have the cold upped a notch. Media forecasts showing Maximum temperatures of 3c or 4c even down south in the big cities, come, the end of the week. Not far removed from my expectations here I think, with a colder scenario slowly developing and snow in the mix by week two or three?

I'm doing the same, following every so often. The impression I'm getting is that the 10th is the pivotal date for colder weather

[nick sussex]

A quick paintjob to explain the trigger shortwave.

In the day 6 , that's circled red , the main upstream low in black.

The reason you must have low shortwave separation is the ridge extension from the limpet high needs an escape route. If those phase energy gets pulled over the top and you'd need a huge amount of upstream amplification to overcome that after that point. This ridge amplifies in response to the more amplified low. You can see the change between day 6 and 7.  The shape of the low moves from the round football shape to more oval and the overall troughing elongates.

As this happens the ridge is forced north ahead of that. At the moment the models are having problems forecasting the movement of shortwave energy in the Atlantic. This makes any forecast more difficult because the phasing or not with the upstream trough and shortwave energy impacts hugely downstream.

 

[feb1991blizzard]

7 minutes ago, nick sussex said:

 

 

That chart is the holy grail in terns of perfectly aligned WAA, hence the end result of the run.

[Seasonality]

42 minutes ago, northwestsnow said:

According to the bbc posted above,2 out of 3 SSWs result in cold for UK..

I think that relates to SSWs that create a split vortex rather than a displacement. The second type I'm pretty sure has a much lower 'success' rate. 

[nick sussex]

1 minute ago, feb1991blizzard said:

That chart is the holy grail in terns of perfectly aligned WAA, hence the end result of the run.

Yes , this type of evolution we’ve seen many times , high edges north shortwave heads se .

We’ve also seen it fail many times aswell ! I’d prefer more distance with the upstream trough and trigger shortwave to increase the margin of error . 

The UKMO is an example of what happens if they phase , no chance of evolving like the ECM .