Model output discussion - after the beast, what next?

[Hammer50]

Looks like the other week was the appetiser and next week is the main course ,

[shaky]

Got a feeling gfs aint got the handle of this easterly yet!!i think its gona bring it forward to saturday on the 12z run!!ukmo is half way house and ecm is the quickest!!

[karyo]

There will be some very frosty nights if the 6z GFS is correct. It keeps us under the cold air all next week (while the 0z had the Atlantic coming in fast) and as the winds fall light some impressive minimum temperatures are likely.

[Purga]

This potential cold spell could be of longer duration than the recent one if GFS is to be believed as we retain the cold uppers (and low level cold) throughout.

The NH chart below is bursting with cold potential!

The run goes on to show mild air pushing in from the SW but I'm not so sure this happen in the current volatile atmosphere !

[Nick F]

Just now, feb1991blizzard said:

Blimey, would have thought a 20 degree difference between sea and 850 and then with steep mid level lapses - low 500mb heights, I would have thought some very big convecntion and as you say surface heating to boot.

I don't think it will be steep enough for deep convection over the North Sea, though happily be proved wrong, as not often we see such cold air cross a cold North Sea in late March, I guess convergence of the easterly flow in the Thames / Wash may have picked up enough moisture for a weak streamer. I would look more inland though for something heavier given surface heating greater now.

[Man With Beard]

ECM clusters this morning: D6 - variations but similar themes of a wedge of heights to our north, allowing an easterly for at least a day or two. Confidence now looking fairly high for this to happen:

Also looking good is the transition to a NW based ridge immediately after: 4 of the 5 clusters at D9 have variations on this

Still could be going by D12 (look at the deep purples to our east, suggestive of a trough and a north-based flow on its back edge for the UK).

Having said that, neither the NE nor the NW ridges really develop into a significant block - so trends beyond about D7 need caution at the moment. But I foresee perhaps two bites at a wintry cherry before the month is out.

 

[Derecho]

No nonsense from the 06z ICON, funnelling the -10C uppers to us by Friday night/Saturday morning!

Edited March 12, 2018 by Quicksilver1989

[Nick F]

Quite a significant drop in temperature on 06z GFS for 3pm in London from +13C on Saturday to +3C on Sunday - when the deep cold arrives!

[bluearmy]

@Man With Beard - six eps clusters out to day 8 says this is still evolving. I think we would be wise to watch rather than assume anything until tomorrow’s runs have hopefully honed in on a solution. Turning cold, probably very cold for a period but detail sketchy. The meto update for the weekend will be interesting to see how much fence sitting they do. 

[Purga]

I always thought the NASA model was best

Blizzards and high wind chill for the SE

[bluearmy]

16 minutes ago, Hammer50 said:

Looks like the other week was the appetiser and next week is the main course ,

IMO, There isn’t currently strong evidence that this would be anything other than desert. The other week was exceptional with thicknesses in the low 500’s and uppers -15/16c for longer than half a day. 

Lets see how this evolves for a few runs before ‘bigging it up’ too much. After what we had at the turn of the month, another cold shot has quite a job to get close to that re surface conditions over several days. 

[stodge]

1 minute ago, bluearmy said:

IMO, There isn’t currently strong evidence that this would be anything other than desert. The other week was exceptional with thicknesses in the low 500’s and uppers -15/16c for longer than half a day. 

Lets see how this evolves for a few runs before ‘bigging it up’ too much. After what we had at the turn of the month, another cold shot has quite a job to get close to that re surface conditions over several days. 

Indeed, we aren't there yet and lots of detail to be resolved.

I'd make two points - we had two or three days of really cold winds cooling the ground before the snow arrived a fortnight ago. This time the more immediate transition will mean snow falling onto warmer surfaces so I have some doubts as to how much snow will fall and settle how quickly (less of an issue in rural areas and with elevation).

Second is although the days are longer, there's huge scope for severe and penetrating frosts with this set up. We know frosts in April and even early May aren't uncommon so late March would be fine for some very cold nights especially if we get clear skies and light winds.

My temperature record in lowland East London was broken on March 1st which was colder than March 11th 2013 and I don't think this next cold wave will approach that in terms of daytime maximum below freezing.

[Derecho]

06z ensembles - slightly less bullish on the cold easterly but nothing to be concerned about yet IMO.

[Daniel*]

10C in London this Sunday according to Beeb okay.... 

the NASA model quite rightly doesn’t get much attention but it certainly caught my attention^ looks more of a snow fest for SE England compared to the last beast. 

There definitely is going to be snow, uncertainty however on whether it will be more scattered or widespread. It would be nice if we had a low bump into cold entirely plausible. I would say the far north it’s likely to be quite dry but cold so not nearly as snowy.

[Norrance]

2 minutes ago, Daniel* said:

10C in London this Sunday according to Beeb okay.... 

the NASA model quite rightly doesn’t get much attention but it certainly caught my attention^ looks more of a snow fest for SE England compared to the last beast. 

There definitely is going to be snow, uncertainty however on whether it will be more scattered or widespread. It would be nice if we had a low bump into cold entirely plausible. I would say the far north it’s likely to be quite dry but cold so not nearly as snowy.

A lot of people said this last time too ( re North).

[bluearmy]

3 minutes ago, Daniel* said:

10C in London this Sunday according to Beeb okay.... 

The meto app has st albans

sat: 4c

sun 3c

i think we learned enough from the last spell that the beeb are struggling on their automated stuff (and a bit more )

[karyo]

Let's secure the easterly with the cold uppers and the exact wind direction and then we can see where most of the snow showers will be.

I think we will have to wait a couple of days for that.

[Man With Beard]

ECM individual ensembles: Feels slightly like dejavu from the end of last month this morning!! Conclusions:

- Deep cold into the UK by Saturday on most of them

- Uppers of minus 13C easily achieved on most, minus 14C on quite a few, and even some minus 15Cs and 16Cs. That's only slightly down on what we were looking at on 28th February.

- A lot of the country affected but some runs localise the impact on either the north or the far SE.

- Most are fairly quick affairs with the deep cold coming and going within 48 hours.

- Snow is MOST DEFINITELY on option on most ensemble runs, with the east coast likely to get a reasonable covering again, but all areas potentially in line to receive soemthing I think?

[chionomaniac]

1 hour ago, Quicksilver1989 said:

Whilst the 06z is updating...



Swingometer for 00z's is here and that is what I call a swing 

Love these ensemble watch that you provide. I'll ignore the latest one lol.

I am terming this one the #minibeastfromtheeast

[Nick F]

Who would've thought late last week that we'd be staring down the barrel of the Beast From The East part 2 this month? Well the model operationals and ensemble guidance certainly weren't, until over the weekend.

It seems the second reversal of the strat zonal winds is propagating down quickly through the week, the models were picking up this impact on the troposphere, but have been unsure how this will affect the upper flow pattern and thus where to build the 500mb heights in spatial extent ... and still there are some differences between GFS and EC as @bluearmy points out - which impacts the surface synoptic pattern.

However, there appears to be general agreement on a Scandi high building by the weekend, which will usher in some cold air – GFS 00z/06z track of deepest cold IMO preferred track over the 00z EC – which looks too far north against the ensemble guidance.

How long the high just to the NE remains in situ will be determined by the upper flow configuration and upper ridge position. GFS operationals this morning have a stronger 500mb ridge close to NE UK which keeps the surface high in place just to our NE for longer and keeping a continental flow going into next week. However, the 00z EC has the 500mb block more to the NW and eventually W – so any surface high building over Scandi quickly removed by troughing digging south, with high pressure building to the west instead to allow a Nly flow to develop.

Ensemble guidance for early next week: 00z/06z GEFS 500mb mean has  more W-E aligned ridging from southern Greenland E into Scandi/North Sea, while EPS has more NW-SE aligned ridge from western UK up to Iceland and deeper troughing to the E.

GEFS EPS

Until the operationals iron out these differences, no knowing if high pressure will remain in situ close to the NE for as long as 00z/06z GFS indicates into next week, the differences are increasingly large between 00z EC and 00z/06z GFS early next week.

Edited March 12, 2018 by Nick F

[mike Meehan]

It is looking like a return match in a week's time with the beast from the east, though it looks more like the little brother of the first one. 

 

Edited March 12, 2018 by mike Meehan

[bluearmy]

@Nick F - thinking back to the last reversal, the models didn’t really appreciate the size of the reversal until after it had occurred. This upcoming one is less intense but you would think that there will be a larger retrogressive signal picked up by he models advise this week progresses 

also, the initial Scandi ridge is predicated on the polar ridge dropping down so less reliant on any WAA as we saw last time. 

I am taken by six eps clusters in the 5/8 day period - Exeter are suitably vague on their update but there is little mention of rain! 

[Frosty.]

Some very interesting charts from the GEFS 6z plus probably the most wintry update a coldie could dare hope for regarding the second half of march and into april..this coldie is very happy!

[Seasonality]

1 hour ago, mike Meehan said:

It is looking like a return match in a week's time with the beast from the east, though it looks more like the little brother of the first one. 

 

Pretty impressive for the time of year though, some parts of Europe more so then others, -18 uppers as far west as Germany this weekend according to latest GFS output.

[Interitus]

14 hours ago, chionomaniac said:

Ahhh another chocolate teapot in your post... I believe the last one froze.

It seems that we are seeing the second response to the SSW with another surge of negative zonal mean u winds heading for the troposphere

 

Don't think that this is a second response directly, this is a separate projected weakening of the vortex. Below are the stratosphere winds (GEOS analysis + f/c) since the SSW which shows that they recovered before an upcoming weakening which begins at lower levels before 10mb -

This is borne out by this morning's GFS forecast, weak troposphere anomaly leads the stratosphere -

In the past few days there has been a strong Asian mountain torque, possibly aided by ongoing Indian Ocean MJO activity -

Along with this, and the contrast of cold Siberian and warm south Asian airs, a fairly strong storm moved into the Pacific from China, seen below with very good divergence aloft  -

Whatever the cause/effect, a Rossby wave packet was initiated over east Asia - here seen in the 200mb meridional wind anomalies (the 'orange blob') around 9th March at 150°E - this is the onset of southerly winds of the wave -

The wave itself progresses eastwards slowly (follow the coloured areas down the chart - phase speed) but the wave packet progresses faster - the group velocity - such that meridional wind anomalies at jet stream level reach the Greenwich meridian by the 16th/17th. This is what causes the (already southerly displaced) jet to dip away to our south into north Africa at that time -