Models, teleconnections and nowcasting

[Jordan S]

Winds become very strong for the southwest later this evening and overnight perhaps as high as 60mph for the Irish sea and coastal parts of southwest England but inland around 40-50mph perhaps a bit more in association with heavy showers and heavy areas of rain. Winds become strong for the rest of southern UK with areas of rain moving through. 

GFS.. 

Icon.. 

Edited December 12, 2019 by jordan smith

[Blessed Weather]

8 hours ago, knocker said:

Still major differences between the ext GEFS and EPS vis the upstream and Arctic profiles so this still needs to be resolved.

(SNIPPED)

Whilst some good agreement between the two major model forecasts out at 19th-21st December, particularly wrt continuation of a strong Jet Stream and Atlantic trough impacting the UK, there is indeed a disagreement regarding forecast heights over the Arctic. These features shown clearly on the 8-10 day NH 500hPa mean height anomaly chart from this morning's 0z operational output:

Although the operational models disagree about the Arctic profile, both the GFS and ECM ensemble members are largely in agreement about the areas of uncertainty upstream of the UK at that time. We'll see if the 12z runs bring any noteworthy changes to this. 

ENS spread:  GEFS spread:

[phil nw.]

This time next week both GFS and ECM operational runs have a similar idea as they both show a Euro.ridge developing and some weakening of the UK trough,

 

Some small differences wrt the exact placement of the surface features as could be expected a week out but the overall picture is of a more south westerly flow as the trough weakens and we lose the colder polar maritime feed.

 

Edited December 12, 2019 by phil nw.
corrected images

[phil nw.]

The 2 mean ht. anomalies 500 hPa charts for day 10 along with days 6-10 850 hPa temperature anomalies.

Similar picture.A trough down the Pacific coast of N.America, Cross polar +ve hts stretching from C.Usa to N.Russia with the Atlantic trough orientated more west -east with a mean west to south west flow into the UK.The Euro ridging showing further east.Temperatures higher than of late.

[Blessed Weather]

Revisiting the GFS 8-10 day NH 500hPa heights anomaly (19th-21st Dec) which has now updated for the 12z run and the model has made a clear step towards the ECM solution, with higher pressure over the Arctic which is now similarly straddling the Pole and encroaching west towards Greenland. And as mentioned by Phil above, the 12z also showing a weakening of the trough to the west of the UK. Here's the two runs for comparison:

GFS 0z run:  GFS 12z run:

[knocker]

An interesting Camborne midday sounding today as it appears to be between the two airmasses  Quite a large inversion 779mb - 688mb above the lower cloud with the narrow dry area before the medium level cloud. Note nearly 100kts at 700mb with the max wind 305/165kts at 288mb

 

Edited December 13, 2019 by knocker

[phil nw.]

There's no real change expected to the mainly unsettled outlook in the coming week.

T72hrs fax and NetWx medium range T72 and T96

the wet conditions expected over the week end gradually easing as pressure starts to rise.Still some showers around with some hill snow but some more noticeable drier slots.We can see by mid-week the Euro ridge nearby giving a better day for many.

However by Thursday signs of another Atlantic system is approaching which heralds a change to a more south westerly flow and less cold conditions into the south west.

The 3 main models at T144hrs NH 

Temperatures generally around or a little below normal.

 

 

 

 

 

Edited December 13, 2019 by phil nw.

[phil nw.]

The Gefs day 10

Quite mild across W and C.Europe under the Euro ridge.

 

[Jordan S]

Like I mentioned earlier today it's worth keeping a close eye on this feature tonight looking stormy for the english channel and the southwest with gusts of 50-60mph possible for the southwest and 70-80mph possible for the english channel perhaps effecting the south coast later too depending on the precise track.. 

Hirlam..

Arome.. 

Arpege.. 

Whether these gusts are exaggerated remains to be seen as Arpege and Arome can at times overdo wind gusts and its dependent on how this system develops but definitely Worth checking observation sites on gusts speeds this evening and overnight for the south and southwest. 

Edited December 13, 2019 by jordan smith

[knocker]

Gusting 55mph here

2100

https://earth.nullschool.net/#current/wind/surface/level/orthographic=-3.96,53.30,2223/loc=-5.202,50.059

[knocker]

Tropopause Fold at Castor Bay at midnight?

[Jordan S]

Certainly a cold wind chill out there in the strong wind feels close to or below freezing for most except the far south and southwest.

Edited December 14, 2019 by jordan smith

[Dorsetbred]

4 hours ago, jordan smith said:

Certainly a cold wind chill out there in the strong wind feels close to or below freezing for most except the far south and southwest.

Yup, we call it winter down here, a breeze and 6C, whilst the rest of the UK, might see sub 0C, however the breeze was cold, at it's peak this morning..

[Jordan S]

Some very strong and squally wind gusts transferring eastwards associated with the remaining areas of heavy rain moving northeast over 50mph possible in some places for England and Wales within the next couple of hours before easing later in the night after the clearance of this rain. The trough responsible likely develops into a closed area of low pressure as it drifts into the north sea perhaps enhancing the wind gusts for east anglia for a time by morning. 

Edited December 14, 2019 by jordan smith

[knocker]

The cold fronts currently orientated across central France > north west Iberia

Upon which a wave will develop and they will start to track north west through tomorrow as warm fronts and bringing rain into the south east

Edited December 15, 2019 by knocker

[knocker]

It is only during the last two days of the ecm det run that it introduces cold air from the north so looking at the the clusters for these is this a realistic percentage play? Pushing it a bit I feel

Edited December 15, 2019 by knocker

[knocker]

This morning's ext EPS is a thing of beauty

much as the weeklies update was indicating

[blizzard81]

1 hour ago, knocker said:

It is only during the last two days of the ecm det run that it introduces cold air from the north so looking at the the clusters for these is this a realistic percentage play? Pushing it a bit I feel

Those lovely orange colours to our north west on those clusters are a thing of beauty. 

[knocker]

The detail for next week is a long way from being nailed down so this is merely the gfs take on it this evening

There is a lot of energy tacking east and interacting with the subtropical high zones which results in a very unsettled picture, interspersed with the odd quieter interlude

[knocker]

A grand ext GEFS mean anomaly this evening The salient points:

Intensification of the vortex

Ridge/trough combination in the eastern Pacific with height rises in the southern States

All of which results in a strong westerly flow across the Atlantic but the trough is in the process of retrogressing allowing the subtropical high to amplify in the vicinity of the UK

Portending more settled conditions with temps trending above average

BANK

Edited December 15, 2019 by knocker

[knocker]

Different detail but the ecm also very unsettled. The danger here is that in this very cyclogenisis friendly environment that we cop another quite nasty storm

[knocker]

The ext EPS is certainly not the same as the GEFS so this still not a settled pattern, albeit more or less in the same ball park. For starters the amplification in the eastern Pacific is not so intense, but still a strong westerly flow exiting the eastern seaboard around the Atlantic trough that has retrogressed, and then backing a tad in the east courtesy of heights building in the vicinity of the UK.

[Blessed Weather]

Looking at the trend from the 8-10 day 500mb mean height anomalies from both ECM and GFS the key takeaway is the weakening of the blocking from the Russian high which allows the anomalous lower heights over the Atlantic to extend further eastward over the UK. Currently no let-up in sight to the low pressure and wet weather domination of UK weather. For comparison, the 3-day mean from the 12th Dec for 19th-21st versus today's 12z for 21st-23rd:

19th-21st Dec  21st-23rd Dec

[knocker]

The run up to Xmas

Outlook - unsettled with a fair amount of detail to be sorted

The North Atlantic 500mb and surface analysis for midnight

Quite a cold start to the day in many areas but at least it's dry. But the frequent heavy showers over N. Ireland and western Scotland will continue through the day, with also a few down the western regions of England and Wales. And rain will steadily encroach the south east courtesy of a couple weakening fronts. Quite a temp spread

Rain from the occlusion will effect N. Ireland and Scotland tonight before clearing all but the far north by morning whilst the rain persists in the south east.

Overall Tuesday will not be a bad day, albeit generally cold. once any early morning fog has cleared but rain rain will persist in the far north of Scotland with a few showers down western coastal regions.

By Wednesday the pattern has become quite complex with a high cell over Greenland with a strong westerly jet south of this running up against the amplifying ridge to the east. On the surface, after a transient ridge and a cold and foggy start to the day, rain and strong winds will sweep across the country late afternoon and evening courtesy of fronts associated with a deep low west of Ireland

By Thursday the main low is still out west whilst rain from the occlusion is still effecting the south whilst another system is developing in the base of the upper trough west of Iberia. But it is now warmer in the south westerly flow

Friday starts okay but the aforementioned developing low continues to develop very quickly and track NNE to be over the country by midday bringing rain and strong winds

Edited December 16, 2019 by knocker

[knocker]

There is a major problem continuing with the gfs from here because it's surface analysis at midday Friday is completely different to Exeter both around the UK and further west in the Atlantic so this has to be kept in mind. And I'm not inclined to go further than the weekend without seeing the GEFs and ecm

So this is the NH profile midnight Sunday as the old low west of Ireland merges with another trough tracking east. All very messy