The hunt for cold - Model discussion (late November)

[MR EXTREMES]

1 hour ago, JeffC said:

I refer back to my comment of yesterday morning. It wouldn't be too much of a stretch to get a situation like 2009, with severe flooding switching to cold with frost and snow within a couple of weeks. 

So long as there's no repeat of the flooding experienced by Cumbria then that would be fine by me. 

totally agree happy to have pv shoved over our side of the pole.

murmurings of a ssw as well nowhere near winters over.still feel there's a change coming in december.

there's plenty of cold to our east and north.

and still on going wave events into the vortex so its nowhere done deal.

although i don't see the unsettled atlantic zonal getting much further east than the uk.

we get any kind of slider then its game on very fine margins at the moment.

[Newberryone]

4 minutes ago, stodge said:

Morning all

Without wanting to sugar coat it too much we are looking at 7-10 days of Atlantic-dominated weather from the middle of next week. We shouldn't be surprised or assume it's the end of winter or anything like that, We often get a milder spell at the beginning of December so this is just normal pattern shifting and changing.

As to what happens before, we'll start seeing some tantalising offerings in the very far reaches of GFS FI before long - my money (and very nice money it is too) is on a pressure rise from the south and mid latitude blocking in the vicinity of the British Isles so not brilliant for fans of snow but fans of cold and especially frost and fog might get a decent spell under a classic winter inversion.

The PV profile is very different to some more recent winters and that has to be of interest though my concern as always with those who want everything to happen in Greenland is the risk of the west based negative NAO which killed the 2010-11 winter at New Year.

For now, the Atlantic will do its thing until it stops doing it and then we can see if we can get anything out of the next amplification. 

Any pressure rise from the south in winter can be fraught with danger for those of a cold weather persuasion. Wouldn't care either to hedge too many bets on frost and fog being much of a player with such a mid latitude block.

[Nick F]

For those forlorn starring down the barrel of mild and unsettled SWly oblivion, bear in mind it can change within a week or so.

Back in early December 2009 it seemed like a similar oblivion …

… but what a difference can happen in 10 days!

With a decent enough amplitude MJO wave moving through 7-8-1 over the coming few weeks, we could see a pattern change in early to mid December as the lag effects of this MJO event moving through the Pacific have impacts on the extra-tropical teleconnections - usually favourably towards blocking returning, mostly likely to the NE, and return of the -NAO.

[sebastiaan1973]

7 minutes ago, Nick F said:

With a decent enough amplitude MJO wave moving through 7-8-1 over the coming few weeks, we could see a pattern change in early to mid December as the lag effects of this MJO event moving through the Pacific have impacts on the extra-tropical teleconnections - usually favourably towards blocking returning, mostly likely to the NE, and return of the -NAO.

But does the MJO wave have enough amplitude? 

[Nick F]

11 minutes ago, sebastiaan1973 said:

But does the MJO wave have enough amplitude? 

Is a good question, some models seem to have decreased amplitude on yesterday's update, but I often find the models aren't always great at depicting the MJO wave in the RMM plots, the VP200 forecasts updated today suggests a fairly coherent wave over the western Pacific still. But will it be coherent enough to change the pattern in early December? No guarantees of course. But there are also other driving forces afoot that could do the job, such as the planetary wave attacks on the sPV which are trying their best to displace it + underlying drop towards solar min in next year or so.

Edited November 23, 2018 by Nick F

[Ventnor Viking]

I love how the UK has the only wedge of mild uppers in the northern hemisphere mid latitudes....you couldn't make it up lol

[tight isobar]

10 minutes ago, Shaftesbury Snow said:

I love how the UK has the only wedge of mild uppers in the northern hemisphere mid latitudes....you couldn't make it up lol

All par for the course...

In advecting warmer air into the polar regions!..and-or scandi-blocking  align.

■-and with the strat becoming toasty @pacific/eurasian sector...its all gravy!

Edited November 23, 2018 by tight isobar

[bluearmy]

6 minutes ago, Shaftesbury Snow said:

I love how the UK has the only wedge of mild uppers in the northern hemisphere mid latitudes....you couldn't make it up lol

newton

karma

law of averages

sods law!

 nothing I am seeing tells me that this is anything but a temporary blip in the blocked and amplified pattern ...... there has to be some mobility around the NH ........ it finds itself in the Atlantic sector for a period ......can’t see it lasting 

[Seasonality]

Stronger Euro Block and lower heights in the med later on in the 06z compared to 00z. *edit: and as run progresses mild air incursion is held back further west

Edited November 23, 2018 by Seasonality

[booferking]

CFS brings in a potent Easterly at the end of week 1 Dec then the high retrograde towards Greenland.

[Ali1977]

7 minutes ago, booferking said:

CFS brings in a potent Easterly at the end of week 1 Dec then the high retrograde towards Greenland.

-16c uppers beyond the west coast of France, pretty impressing before mid Dec if it were to happen. 

[frosty ground]

CFS post being made, Hunt for cold has gone beyond the GFS.

No surprise the atlantic is going to win out, whilst the opportunity for a cold outbreak was there it was never favoured

On to the next hunt, not using the CFS thou not unless my tea leafs run out that is. 

[Ventnor Viking]

53 minutes ago, bluearmy said:

newton

karma

law of averages

sods law!

 nothing I am seeing tells me that this is anything but a temporary blip in the blocked and amplified pattern ...... there has to be some mobility around the NH ........ it finds itself in the Atlantic sector for a period ......can’t see it lasting 

absolutely - a shift of energy is always needed for a pattern change.

[booferking]

10 minutes ago, frosty ground said:

CFS post being made, Hunt for cold has gone beyond the GFS.

No surprise the atlantic is going to win out, whilst the opportunity for a cold outbreak was there it was never favoured

On to the next hunt, not using the CFS thou not unless my tea leafs run out that is. 

Nothing wrong with using all tools at your disposal Day 10 blocking will be back you can see this trend appearing in GEFS and its only going to grow peace.

Edited November 23, 2018 by booferking

[Ventnor Viking]

55 minutes ago, tight isobar said:

All par for the course...

In advecting warmer air into the polar regions!..and-or scandi-blocking  align.

■-and with the strat becoming toasty @pacific/eurasian sector...its all gravy!

Agreed. How many times do we see a pattern change appear quickly within the models? Its very rare that a cold pattern is modelled well in advance.

[feb1991blizzard]

13 minutes ago, Ali1977 said:

-16c uppers beyond the west coast of France, pretty impressing before mid Dec if it were to happen. 

Academic of course but also another thing to remember, last March was good but we had nearly -16c uppers then, IF (and it probably never would) -16c happened to make it across the channel / North seas into this country this early in the season, it would mean oblivion here, remember the SST's are higher at this time of the year, we only needed around -10 to-12c in late Nov 2010 for 6 inches of snow in under 3 hours here on the Western side of the pennines, -13c hardly gave me anything with one Easterly in Feb / March 2013, the earlier in season, the more leeway you have with uppers (although lower probability to get cold uppers of course) needed to generate steep convection, of course you then want a steep lapse rate between 850 and 500mb as always but as long as you have this and as long as the uppers aren't marginal, you can get a memorable spell - -10c can mean heavy convective snowfall for many areas of the country.

[carinthian]

4 hours ago, carinthian said:

 UKMO pick of the models out to 144t for prolonging the colder wind flow for a while longer. The latest run not as progressive as the last one.Hint of a slower transfer for veer towards a milder wind flow to take place around mid -week. Until then will start to feel cold especially as the wind picks early next week ( Chart below 850mb temps Wed morning ). Longer term, I still have doubts as to the movement and speed of progression of the low coming the way of the British Isles. Will get an update with thoughts from over here later this morning.

C

Period 120-168t still holds some doubts regarding the transience to remove the block to the NE with the advancing Atlantic flow. The track of the low and the forecast exit speed through the British Isles not nailed. Their own model shows a much slower process to evolve with the low to be between Scotland and Southern Scandinavia between period 168t-192t. with a possible trough development to later in this period. So that would indicate a lower latitude positioning of the low than shown by GFS, possibly more akin to what UKMO runs may be showing (day7 to9). Longer term days 10-15 , strong ridging NE across the UK  being indicated. Hope this helps, but looks like the forecast of a milder incursion into the British Isles could be limited due to renewed pressure rises.

C

Edited November 23, 2018 by carinthian

[Derecho]

06z Swingometers

December 1st has started to trend a bit milder recently though average temperatures are more likely for this date with many runs showing a westerly flow

The December 6th swingometers though have started to get more interesting. A sign things may settle down once again as we start getting into December?

Plenty of cold to our east but not close enough to here. Some reisdual cold air from that west based -NAO may briefly make its way over us giving the odd day of colder westerly winds but expect some mild sectors to make their way across also.

[Methuselah]

I think I've found a way of being optimistic...

Here's the latest T+384, which show a hint of the Atlantic HP ridging toward Scandinavia:

And, should it go the whole hog, we may well being seeing more of these:

 

Then again, our old friend, the GFS para is having none of it!

Edited November 23, 2018 by Ed Stone

[Glacier Point]

Compare days 1-5 GEFS z500 mean height anomaly:

With days 11-15:

Substantive shift with mean trough in the North Pacific being replaced with a mean ridge.

That ties in with this:

MJO fairly rapidly moving through the Western Hemisphere and into the Indian Ocean.

That's a Nina like cycle within a broadscale Nino base pattern. Usually this type of juxtaposition is good from a -NAO evolution.

Next evolution would be for the MJO / convective signal emerging across the Maritime Continent and associated tropospheric impacts to the stratosphere, which continue to look like mid to late December, with perhaps earlier evolution of a -NAO through more conventional (MJO/GWO) feedbacks.

Edited November 23, 2018 by Glacier Point

[tight isobar]

1 hour ago, Glacier Point said:

Compare days 1-5 GEFS z500 mean height anomaly:

With days 11-15:

Substantive shift with mean trough in the North Pacific being replaced with a mean ridge.

That ties in with this:

MJO fairly rapidly moving through the Western Hemisphere and into the Indian Ocean.

That's a Nina like cycle within a broadscale Nino base pattern. Usually this type of juxtaposition is good from a -NAO evolution.

Next evolution would be for the MJO / convective signal emerging across the Maritime Continent and associated tropospheric impacts to the stratosphere, which continue to look like mid to late December, with perhaps earlier evolution of a -NAO through more conventional (MJO/GWO) feedbacks.

Decent summary as-per..

And id go with that..

-nao..#rapid movement!!

@pac punching

 

 

...cannot upload PNA/NAO forecasts..as per post !!!?

 

The canadian ones note the ridge well...

Edited November 23, 2018 by tight isobar

[stodge]

3 hours ago, Newberryone said:

Any pressure rise from the south in winter can be fraught with danger for those of a cold weather persuasion. Wouldn't care either to hedge too many bets on frost and fog being much of a player with such a mid latitude block.

Rather depends on position and orientation of course. An intense HP centred just to the south of the UK can be quite clear and leave southern areas cold, frosty and foggy. Ideally, you want the mid latitude block to the east so cold SE'ly air is drawn in from a frigid continent but that tends often to be a cloudy airstream.

An HP directly over the UK centred over central or northern England, while technically mid latitude, can often produce a cleaner solution but you do get areas of cloud trapped which circulate so you might get frost one night but not the next.

The other aspect of my comment is that very cold scenarios can result from the HP over Iberia transferring NE into Scandinavia  That is one of the three ways you get a Scandinavian HP - the other two are a) the Eurasian HP building west or WNW or b) the Arctic HP building south or South-South-West. The latter is extraordinarily rare, the former less so and you can have an intense HP (say 1050MB or higher) controlling our weather but centred over Finland and building a strong ridge westward.

The famous 1962-63 winter cold spell started from the Iberian HP moving NE. If you look at the Archive charts on Meteociel, you can see how from 20-22 December, the Iberian HP moved NE over the British Isles and phased with an HP to the east to create an intense block which was centred to the east of Denmark on Christmas Eve and immediately retrogressed as a strong Arctic storm containing a portion of the PV moved ESE near the Pole. By the 27th, the HP was over Greenland and a frigid NE'ly was impacting on the British Isles and the rest is history.

It's also worth noting where the core PV was at that time.

[johnholmes]

A bit picky but the HP was more like the Azores ridge?

[Mike Poole]

Block putting up more of a fight on the ICON early doors, at T96.

6z at same time:

[weathergeek]

I expected it to be quieter in here but I'm hoping from seeing the continued "mild blip but returning to cold" that the Meto extended says and the fact that some models are also supporting this means we'll be back to some juicy charts after the initial milder weather. A potential SSW and the larger picture of PV/NH profiles mean there is a lot of potential still to come!