Model output discussion-mid Autumn and beyond

[knocker]

Compared to the GEFS and NOAA (which is of course an automated forecast today) the EPS medium,term mean anomaly is more amplified upstream with quite an intense vortex/ Alaskan trough and thus the Atlantic trough further east which facilitates the energy suppressing the subtropical ridge. Oh my.

Edited December 2, 2018 by knocker

[knocker]

As mentioned in the other thread this is a critical period of the evolution and the gfs brings the next low north and then east as the subtropical high ridges in mid Atlantic.so more rain on Sat/Sunday with the surface wind veering northerly

The ridge slides east over the UK during the beginning of next week but much is going on upstream with explosive cyclogenesis occurring along the baroclinic zone of the eastern seaboard and all of this energy exerts tremendous pressure on the ridge. And just to reiterate this is according to the gfs

[knocker]

Predictable the upstream developments from the ecm post T144 are different which leads to a slightly different energy distribution and thus adjustments downstream. All quite fascinating.

On another note I understand an emergency meeting of COBRA has been called. Apparently a few sightings of trigger shortwaves have been reported, and even the odd spoiler.

[knocker]

Yesterday's blog by Jack Sillin is not bad if you want and overall perspective.

https://blog.weather.us/potential-winter-storm-to-usher-in-warmer-pattern-for-east-coast-mid-month/

[knocker]

The EPS mean anomaly is not keen on building a substantial high cell to the north east. Quite intense low pressure/trough over the Pole and Alaska, a ridge north east N. America  with a trough Greenland into the central Atlantic leads to westerly flow diverging over the UK to the positive and negative zones to the east. One would have thought this portends changeable weather with a N/S bias with temps around average, perhaps a tad below.

Edited December 3, 2018 by knocker

[phil nw.]

Next week continues to suggest some change with the modeling of  a sub-tropic ridge building north across the UK.

The evolution showing it to commence around days 6-7 and by day 9 appears to be centred around the UK

Latest GFS/ECM mean 500hPa

A quieter colder interlude for perhaps 3 or 4 days with night frosts but already more energy is waiting upstream from that Canadian/Greenland trough to test the resilience of the fledgling high.

[knocker]

And then at the beginning of next week the ridge that amplified to the west of the UK comes under pressure from the energy emanating upstream with more explosive cyclogenesis from a low that formed east of the Carolina's. Followed quickly by another that started life across the southern states

[knocker]

The EPS mean anomaly this evening is still not happy vis a block to the north east. More inclined to the east European high ridging north west. And with low pressure over the Med and the atlantic trough fairly adjacent the still strong westerly exiting the eastern seaboard has plenty of puff left over the UK albeit it is starting to diverge courtesy of the aforementioned ridge. Weather changeable with temps a tad below average.

It should be added that the GEFS and NOAA are somewhat at odds with this with a more defined vortex and downstream amplification which facilitates the Azores ridging north east and a more marked divergence to the low pressure to the south east. A much more settled scenario for the UK. Obviously the detail vis the medium term evolution is a long way from settled.

Edited December 3, 2018 by knocker

[knocker]

Moving past the weekend with the ecm by T144 the low pressure has moved to the east with amplification is occurring to the west. This theme continues over the next 24 hours with the ridge being squeezed over the UK.giving a very cold morning on Thursday with widespread negative temps.

By T192 the trough/ridge axis over North America, not only initiates massive WAA in the east ,but diverts the strong north Pacific jet resulting in twin flows exiting in the east coast and then around the now intense Atlantic trough which also promotes WAA and isolates the high cell to the north.  Which is where I think I'll leave it

Of course the good news is fi you get a negatively tilted high cell to the north east it can act as barrier and stop cold air spilling south

 

 

 

Edited December 4, 2018 by knocker

[phil nw.]

Just looking further on to day 10 and the mean 500 hPa charts from the ECM/GFS and GFS(p) show the Scandinavian high giving way to the Atlantic .

the building high currently looks to have a 3/4 day life span before the westerlies try to move in again.

[knocker]

The ext EPS mean anomaly continues to retreat quite rapidly from the amplification towards the end of the det. run. Much along the lines of the latest EC46. Good to see the ecm leading the way

 

Edited December 4, 2018 by knocker

[Summer Sun]

Anything close to JMA and we'd be looking at quite a major storm

[knocker]

What happens next week, according to this morning's gfs. is essentially about energy distribution imo. Illustrated by the NH jet profile at T150

Thus the ridge is put under massive pressure from the two energy flows  which distorts it north east whilst at the same advecting the colder air from the European trough west underneath and across the UK. Thus the cold air gets established during the week but the energy battle is ongoing.

The beauty of this pattern orientation is that it keeps the cold polar air out of harms way.

Edited December 5, 2018 by knocker

[knocker]

The em pretty much on the same page as the gfs with obvious differences vis details but it's a bit early in the piece to worry about them.

[knocker]

The ext EPS mean anomaly still indicating the the amplification is of a transient nature.

[knocker]

Whether it is right or wrong what the 06 gfs is showing is the very strong jet running around the amplified ridge/trough axis over N. america, with storms developing across the southern states and in the baroclinic zone along the eastern seaboard where explosive cyclogenesis quite often occurs. This is also aided and abetted by SST anomalies

.

[knocker]

The evolution of the ecm towards the end of the run appears to be very much down to the pattern change upstream with strong ridging in the east with the north pacific and subtropical jets exiting from the north and south of the east coast which drives the deepening depression into mid Atlantic

[knocker]

And following on from the comments vis the upstream pattern changes. The medium term mean anomaly continues to shift it east and thus the trough ends up over the UK with a NW upper flow,

 

[Man With Beard]

Non cold news... It's probably the GFS going dolally, but worth posting - just the 110-120 khm mean wind speeds on the 14th then:

[knocker]

Moving on a little with the gfs which develops another low in the aforementioned upper trough around the Newfoundland area which tracks east and deepens very rapidly. (more Explosive cyclogenesis) All of which pushes a front against the block over the UK. And this essentially is the scenario through midweek with the two energy flows battling the block with the UK at the coal face

[knocker]

A quick look upstream on the ecm at T144 as it illustrates a point I was attempting to make yesterday regarding the twin energy flows (connected to the Polar and subtropical jets) exiting the eastern seaboard along the baroclinic zone which is the breeding ground for cyclogenesis.

Expanding this theme over the next 60 hours as rapid cyclogenesis does occur and the Atlantic is dominated by vigorous depressions which move east across the UK.

Edited December 6, 2018 by knocker

[knocker]

The EPS remains consistent with the pattern change upstream and the knock on effect downstream. Keep still my beating heart

 

[knocker]

I'm not going to go into the ins and outs of the 06 gfs but just to note that the upstream pattern change is still being strongly indicated. Apart from anything else the cold trough and arctic plunge down the eastern US is replaced by subtropical ridging and WAA with a massive amount of energy exiting the east coast across the Atlantic. So the potential is there for some intense depressions  certainly worth keeping a wary eye out

Edited December 6, 2018 by knocker

[Summer Sun]

To think only yesterday morning some folk on the cold thread were binning GFS 06z when it developed that deep low in the Atlantic effectively cutting off the cold air. 24hrs on we have pretty much unanimous agreement across the board for this scenario

[frosty ground]

48 minutes ago, Summer Sun said:

To think only yesterday morning some folk on the cold thread were binning GFS 06z when it developed that deep low in the Atlantic effectively cutting off the cold air. 24hrs on we have pretty much unanimous agreement across the board for this scenario

Ignorance of the Data is prevalent in that thread